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anza_proposal_1redThe ANZA Seismic Network utilizes state-of-the-art broadband sensors and 24-bit dataloggers combined with real-time telemetry to monitor local and regional seismicity in southernmost California. The goal of this project is to provide on-scale digital recording of high-resolution three component seismic data for all earthquakes, provide real-time data to other regional networks and the USNSN, and provide near real-time information to the greater San Diego community. This proposal requests funds to support the continued operations of the ANZA network.

The ANZA network has been a leader in developing techniques for real-time data delivery over the Internet. To effect rapid data transfer to TriNet routinely transfer all the ANZA data within ten seconds of real-time. In this way, the broadband data is seamlessly integrated in the Caltech/USGS real-time data processing system. The ANZA network exports data in real-time to the IRIS: Data Management Center where it is automatically archived and is immediately available to the seismological community. Real-time data exchanges between UCSD – UC Berkeley and UCSD – University of Nevada-Reno have been operational since late 1998.

The ANZA network enhances the broadband coverage provided by the TriNet in southernmost California. ANZA stations are designed to operate in remote areas without any supporting infrastructure such as AC power, telephone or computer communications. Each station can operate using solar power and all communications between stations and the IGPP are dedicated spread spectrum radio links. The current configuration of the ANZA network will allow for on-scale recording of local events with magnitudes less than M ~ 5. At present, over 32,000 events have been recorded during the 18 years of continuous operation. The median station data return rate is 99.22%.

camp stevensTo provide better coverage in the metropolitan San Diego area, they operate a station on Mt. Soledad in La Jolla. This station provides extended broadband coverage to San Diego county and the offshore region complementing the nearest TriNet stations at Barrett Junction (BAR), Julian Camp Stevens (JCS), and Mt. Palomar (PLM), all located in rural San Diego county. In the UC/CLC Campus Earthquake Project – Broadband Seismic, a set of Borehole Accelerometer have been installed next to the Thornton Hospital on the UCSD campus. The Thornton station provides the only real-time strong motion data from urban or suburban San Diego.

Borehole AccelerometerIn keeping with the spirit of cooperation which has characterized seismological research at Anza, and consistent with the scientific motivations of the ANZA network since its establishment, we will coordinate our research and operations effort with the work conducted by TriNet and with SCEC. We will continue to provide real-time data to the regional networks: TriNet, the University of Nevada-Reno, UC Berkeley, CICESE; to the USNSN, IRIS DMC; and to any other end user who requests data.

In 2001-2004 we propose to continuously operate the following field configuration:

  1. Fourteen 3-component broadband stations. All stations using Streckeisen STS-2 broadband seismometers. 24-bit A/D resolution on all broadband channels.
  2. Borehole strong motion array at Thornton Hospital in San Diego.

In addition, we plan to accomplish the following data processing goals:

  1. Continue to keep a complete and concurrent archive of the ANZA waveform data at the IRIS DMC in real-time.
  2. Determine routine locations and source parameters for all events.
  3. Maintain updated maps/web sites showing local seismicity based on our real-time catalogs.

Significance of Project

Introduction

The ANZA Seismic Network utilizes state-of-the-art broadband sensors and 24-bit dataloggers combined with real-time telemetry to monitor local and regional seismicity in southernmost California (Figure 1). The goal of this project is to provide on-scale digital recording of high-resolution three component seismic data for all earthquakes, provide real-time data to other regional networks and the USNSN, and provide near real-time information to the greater San Diego community. This proposal requests funds to support the continued operations of the ANZA network.

Figure 1. The ANZA seismic network. Current ANZA stations are designated by yellow triangles. The thick blue line shows the microwave telemetry path between Toro Peak and Mt. Soledad near IGPP in La Jolla. Broadband TriNet stations are marked by white squares. Seismicity is marked by red dots. The Interstate highways are marked in black and dashed red lines are faults of interest.

The ANZA network has been a leader in developing techniques for real-time data delivery over the Internet. Through the joint efforts of the personnel at the USGS in Pasadena and Caltech, we developed a system in 1995 which sent phase picks and event waveforms to the Southern California Seismic Networ (SCSN). After testing and evaluating this procedure, we determined that although it worked well, the optimal solution would be to have a direct data feed without the delays caused by intermediate processing steps. By the end of 1996, we had implemented the Object Ring Buffer (ORB) real-time software developed by the University of Colorado supported by funding from IRIS. To effect rapid data transfer to the SCSN, and to its successor TriNet, we installed an ORB server on a computer at Caltech, wrote a software module to interface with the TriNet system, and use this mechanism to routinely transfer all the ANZA data within ten seconds of real-time. In this way, the broadband data is seamlessly integrated in the Caltech/USGS real-time data processing system. Initial procedures for the ANZA network to access TriNet real-time data are now being jointly developed. Real-time data exchanges between UCSD – UC Berkeley and UCSD – University of Nevada-Reno have been operational since late 1998. Mechanisms are in place for the USNSN to access ANZA network real-time data using their Virtual DataLogger (VDL) software.

The ANZA network enhances the broadband coverage provided by the TriNet in southernmost California. ANZA stations are designed to operate in remote areas without any supporting infrastructure such as AC power, telephone or computer communications. Each station can operate using solar power and all communications between stations and the IGPP are dedicated spread spectrum radio links. Two ANZA stations (BZN and WMC) have developed significant cultural noise over the past several years. Following discussions with Dr. Egill Hauksson from the TriNet, we have decided to redeploy these stations towards the south and east of the existing ANZA stations, in the Borrego Valley at the former SCSN single component analog sites, COY and BRG. Final permission for upgrading these stations was received from the Anza-Borrego State Park in May, 2000.

The ANZA network is centered around the Anza segment of the San Jacinto fault zone (Figure 2) which has a maximum expected characteristic earthquake magnitude of 7.5 (Working Group, 1995). This segment of the San Jacinto fault zone is one of the greatest seismic hazards to San Diego county. There is a high level of microseismicity (Ml < 4.5) in the Anza region. It is also located in a region where there is a large number of significant events. The 1986 North Palm Springs (Mw = 6.2), 1987 Superstition Hills (Mw = 6.5), 1987 Elmore Ranch (Mw = 5.9), 1992 Joshua Tree (Mw = 6.1), 1992 Landers (Mw = 7.3), 1992 Big Bear (Mw = 6.2), 1999 Hector Mine (Mw = 7.1) have all occurred within 100 km of the center of the ANZA network since it was installed in 1982. In addition, the Southern California batholith is widely exposed on both sides of the San Jacinto fault near Anza and provides for exceptionally low-loss and homogeneous transmission paths, and consequently high accuracy in determining locations and source parameters (Scott, 1992).

Figure 2. Major earthquakes in historical times in the southern California region. Surface ruptures are defined by the dark gray lines and epicenters are designated by circles scaled by magnitude. The ANZA network is centered on the middle part of the San Jacinto fault zone.

On 1 October 1982, the ANZA network became operational when eight of the ten stations began delivering data in real-time to IGPP/UCSD. In December 1989, the data logging system was upgraded with new equipment which enhanced the capabilities of the network. The improvements include remote control of gain and calibration circuits at each station as well as synchronous sampling of all stations in the network. The network implemented 24-bit A/D converters in 1993 and multiple sample rates in 1994. In December 1999, all radio telemetry links were upgraded to use either the 900 Mhz or the 2.4 Ghz spread spectrum bands. The current configuration of the ANZA network will allow for on-scale recording of local events with magnitudes less than M ~ 5. At present, over 32,000 events have been recorded during the 18 years of continuous operation.

To provide better coverage in the metropolitan San Diego area, we operate a station on Mt. Soledad in La Jolla (Figure 1). This station provides extended broadband coverage to San Diego county and the offshore region complementing the nearest TriNet stations at Barrett Junction (BAR), Julian Camp Stevens (JCS), Mt. Palomar (PLM), all located in rural San Diego county. In the University of California Cooperative Laboratory/Campus (uc/clc campus earthquake program, a set of borehole accelerometers have been installed next to the Thornton Hospital on the UCSD campus. The Thornton station provides the only real-time strong motion data from urban or suburban San Diego. The data from these strong motion sensors are included into the ANZA real-time processing system and transmitted to TriNet in real-time. Borehole accelerometers have also been installed at UC Santa Barbara and UC Riverside as part of the UC CLC project which telemeter real-time data to the ANZA network through the Internet. In addition, two new stations will be provided from internal institutional funds over the next two years.

However, even with these additional stations, San Diego will still be severely underserved. In terms of population, San Diego County is the fourth largest county in the entire U.S. San Diego County is growing rapidly, with a current population of 3 million people (Appendix A). The City of San Diego is the sixth largest city in the U.S. The gross regional product for San Diego County for 1999 was 92 billion dollars. Continued funding of the ANZA network will enable us to provide near real-time information on seismic activity to the San Diego community. In addition, UCSD is ideally situated to serve as a backup real-time processing center to assist TriNet in emergency situations.

Network Instrumentati

Broadband Stations

The current ANZA digital telemetry system (Figures 1 and 3) is designed to accommodate up to 32 three-component, remote, digital seismic stations with sampling rates of 100, 40, and 1 samples per second per component. At present, the data from thirteen stations are transmitted via 900 Mhz spread spectrum digital radio link to a relay station on the 2655-m summit of Toro Peak. A fourteenth station (TRO) is located on the summit of Toro and is connected to the system by wireline telemetry. The stations YAQ, MONP, and SMTC, provided by internal IGPP funding, were added to the ANZA network in 1997. On Toro Peak, data are recorded on a Sun computer which sends data over a 2.4 Ghz wireless bridge to Mt. Soledad in La Jolla and thence to IGPP at Scripps Institution of Oceanography. All components of the system have a battery backup power system or an uninteruptible power supply to minimize the possibility of losing data.

Figure 3. Data flow through the ANZA network. Data packets are sent from the stations to Toro Peak via spread spectrum radios. From Toro Peak the packets are retransmitted to Mt. Soledad and on to IGPP using a wireless bridge. At IGPP the data packets are both processed locally in real-time and sent over the Internet to Caltech, UNR, UCB, IRIS DMC, CICESE, and PEPP. Data are stored locally and at the IRIS DMC.

At each remote station there is a Streckeisen STS-2 seismometer, digitized by a Reftek 72A-08 datalogger. The firmware and telemetry systems were upgraded in December, 1999. These upgrades were designed and field tested by IGPP as part of the IRIS PASSCAL broadband array during deployments in northwest Colorado (1997-8), South Africa (1998-1999), southern California (1999) and Montana (1999-present).

The terminus for the spread spectrum portion of the telemetry is on Toro Peak (Figure 3). A wireline telemetry data stream from a local seismic station (TRO) is received along with the spread spectrum radio signals from the remote stations. The network time is provided by a single GPS synchronized clock located on Toro Peak. The time data is broadcast to all the remote stations on a spread spectrum radio link using a synchronous timing feature in the Freewave radios. Each of the one-second data buffers for each station-channel is received by an IGPP Data Concentrator which sends data packets to a local Sun computer. The Sun forwards data over a wireless bridge link to IGPP using a standard IP protocols, and also provides several weeks of local backup data storage. The microwave data link utilizes Glenayre equipment operating in the 2.4 GHz spread spectrum band. A 1-watt transmitter at Toro Peak, feeding a 2.7-m dish antenna, provides a 34 dB signal-to-noise ratio over the 112 km path to Mt. Soledad in La Jolla where an identical antenna receives the signal. The link from Mt. Soledad to IGPP, 3.2 km away, uses a 0.1 watt transmitter and a pair of 0.7-m dish antennae. The current maximum bit rate for the microwave system is 512 Kbps. As a result of this upgrade, the data return rates have been spectacular. Since the beginning of 2000, the median data return rate for ANZA network stations is 99.22%, and only one station has less than 98.66% data return!

Strong Motion Stations

As part of the UC-CLC project, borehole and surface strong motion accelerometers were installed to characterize site effects on the UC San Diego, UC Riverside, and UC Santa Barbara campuses. Data from these stations are telemetered in real-time over the Internet to the ANZA network operations center where they are included into the automatic location routines, processed, and archived. The ANZA system is designed to accept future real-time strong motion stations located in the San Diego area, if funds for new stations become available.

Real-Time Processing and Data Distribution

At IGPP, data are received by a SUN workstation (Figure 3) operating the Antelope real-time processing system developed by Boulder Real Time Technologies, Inc. (http://www.brtt.com). The Antelope system is a complete real-time system which includes estimating P and S wave arrival times, event detection in multiple frequency bands, event triggers, location and magnitude estimation, data distribution, and data archiving. The existing Antelope system can provide a ring buffer capacity of 48 hours of data for the 17 station network. In addition, a complete disk resident waveform database is kept online containing the most recent 40 days of data. The Antelope Real-Time system performed extremely well during the very active Hector Mine aftershock sequence starting in October, 1999. Two analyst reviewing data, working eight hours per day, were able to process 2603 events in 22 days, completely eliminating the backlog of events.

During the last three years, improvements to hardware and software have led to a more reliable and a higher resolution system. In the first15 years of operation (1982-July 1997) the ANZA catalog contained 15,000 events. Since July 1997, the catalog has increased by 17,000 events!

Real-Time Waveform Data Delivery to TriNet

Using the Antelope system, all waveform data are delivered via the Internet to the TriNet data center (Figures 3 and 4) where the ANZA data are included in the TriNet real-time event association, location, and magnitude estimation processing. ANZA waveform data are received at Caltech by the TriNet system within 5 to 10 seconds of real time. The TriNet catalog, which includes the ANZA network data, is the authoritative catalog for southern California and is contributed to the composite earthquake catalog of the CNSS.

Figure 4. Real-time data distribution and data exchange using the Internet. TriNet, UNR, UCB, CICESE, Indiana University — Princeton Earth Physics Project (PEPP), and the IRIS DMC all receive ANZA data in real-time. Data from selected UNR (blue triangles) and UCB (red triangles) are also received at UCSD.

Real-Time Data Exchange

In the Fall of 1998, we started looking into the concept of a “Virtual Seismic Network” (Harvey, et al. 1998; Pavlis and Vernon, 1998; Vernon and Wallace, 1999). This concept is based on the idea that it would be possible to use available data sources on the Internet from other regional networks to augment the coverage of each network while minimizing the operational costs. As part of this project, real-time data exchanges were established between UCSD and UC Berkeley, UCSD and the University of Alaska, and UCSD and the University of Nevada-Reno (UNR) (Figure 4). This testing provided a big return during the Fall of 1999. The Hector Mine earthquake and aftershock sequence occurred between the UNR and the ANZA networks (Figure 5). The real-time automatic location algorithms of each network would locate a significant number of the aftershocks close to or inside each network. This is especially important for the UNR network since the biased locations were near the Nevada Test Site and Nuclear Repository Site and UNR has very stringent reporting requirements for events near these sites. By integrating waveforms from both networks together in real-time, both UNR and ANZA were able to accurately determine these locations, eliminating significant amounts of work for both groups. In April 2000, a real-time data feed was started between UCSD and CICESE in Ensenada, Baja California. We intend to continue providing real-time data to other regional seismic networks and remote users.

Figure 5. Hector Mine mainshock and aftershocks recorded by ANZA and UNR networks. By exchanging data in real-time, both UNR (orange and blue triangles) and ANZA (red triangles) were able to eliminate location biases in each of their networks. The ANZA network used the UNR stations marked by blue triangles.

Data Review and Archive

The routine processing occurs on a daily basis. All new seismic data are automatically copied to DLT tape on a daily basis for off-line storage at UCSD. The next step is to review the automatic P and S phase picks from all events. The hypocenters and magnitudes for all events are calculated. Standard spectral source parameters are calculated for all events within 50 km of the network. Teleseismic phases are associated with the QED (which is also updated daily via the Internet) and PDE catalogs. Finally, these parameters are stored in a permanent on-line Datascope relational database which includes complete event segmented waveforms.

All 40 and 1 sps data (BH, SH, LH) and event segmented 100 sps data (HH, HL, EH) data are sent directly to the IRIS Data Management Center (DMC) in Seattle, Washington for permanent archiving and data distribution. In November 1999, a Sun computer running the Antelope software was installed at the IRIS DMC. At this time we started transferring ANZA data over the Internet to the DMC in real-time where automatic processes move these data into the permanent DMC archive on a daily basis (Figure 4). This is an extremely reliable mechanism for archiving data at the DMC, saving time for personnel at the DMC and UCSD, saving the costs of shipping and tapes, and making data immediately available to the seismological community. Appendix B shows the requests for ANZA data at the IRIS DMC since December 1997.

Education and Outreach with Web Based Real-Time Access

The ability to supply accurate data and information to both the scientific community and the general public in real-time is realizable. Within hours after the Hector Mine earthquake stuck southern California (2:45am local time), our initial webpage (http://eqinfo.ucsd.edu/special_events/1999/290/a/index.html) was available to the public detailing the location, magnitude, and recorded waveform plots of the event. Extracted waveforms in SEED format were immediately available and requests for SAC format data were also accommodated for the scientific community. Maps on these websites were updated daily to display the latest aftershocks and waveforms were provided for the most significant aftershocks.

A very popular site among visitors to our webpages is the real-time map showing events recorded by the Anza network (http://eqinfo.ucsd.edu/current_earthquakes/anza/local.html). There are actually two pages: one for teleseismic events and a second for local events. Both pages list all events that have been recorded in the previous two weeks with maps that display each event scaled to magnitude and color coded by time. Maps are updated every 30 minutes as new events occur or are reviewed by an analyst. We also maintain links to other sources of seismology web sites.

An important aspect of our education and outreach efforts is our real-time data delivery to the Princeton Earth Physics Project (PEPP). Professor Gary Pavlis, at Indiana University, distributes ANZA data to high school students nationwide as part of the PEPP program (http://aesn.geology.indiana.edu/). In addition, the ANZA network provides real-time data to San Diego State University for seismic information displays and media access.

We now have a prototype webpage that allows real-time display of waveforms to anyone that has internet access (http://epicenter.ucsd.edu:5804). Currently, it displays all waveforms for a given array in 1 hour or 12 hour time windows with automatic detections, triggers, and arrivals highlighted. We are working on increasing the flexibility of the program to allow the user to specify which station and channel they would like displayed and the length of time needed. A similar technique will also be applied to allow users to display waveforms for a single event.

Seismic Hazards of the Region

The southern California region has generated nearly 50 magnitude 6 or greater earthquakes since 1850 (Ellsworth, 1990). Sixty percent of these moderate to large earthquakes are associated with the San Andreas and San Jacinto fault systems and their continuations into Baja California. It is interesting to note that only seven of these events have significant surface rupture. These events include the 1857 Fort Tejon (Mw = 7.8) along the Cholame and Mojave segments of the San Andreas, the 1940 (Mw = 6.9) and 1979 (Mw = 6.4) on the Imperial Fault, the 1968 (Mw = 6.5) Borrego Mountain and 1987 (Mw = 6.5) Superstition Hills located on the southern San Jacinto fault, and the 1952 (Mw = 7.5) Kern County, the 1992 (Mw = 7.4) Landers, and the 1999 Hector Mine (Mw = 7.1) which are not directly associated with the San Andreas-San Jacinto fault system. These historical surface ruptures are shown in Figure 2 which also highlights the two major sections without significant surface offsets: the San Bernardino and Coachella Valley segments of the San Andreas fault and the San Bernardino, San Jacinto Valley, Anza, and the Coyote Creek segments of the San Jacinto fault.

The San Jacinto fault zone is one of the most active strike-slip faults in southern California. The long-term slip rate is 1 cm/year, determined from 29 kilometers offset of geologic formations across the fault in the last 3 million years (Sharp, 1967). Recent measurements of offset sediments in the Anza Valley yield a similar slip rate (Rockwell, et al. 1990). The Anza segment of the San Jacinto fault zone has been identified by Thatcher et al. (1975) as a seismic slip gap for a 6 < M < 7 earthquake. The study of Sanders and Kanamori (1984) revealed a 15 km element of the estimated seismic gap that has been includely aseismic in modern times. Klinger and Rockwell (1989) trenched the San Jacinto Fault at Hog Lake located in the center of the Anza seismic gap and found evidence for surface rupture from three events since 1210. Additional evidence suggests that these events occurred about 1210, 1530, and 1750.

In 1988, the Working Group on California Earthquake Probabilities (USGS Open File Report 88-398) defined the Anza segment to be the 50 km section between the southern end of the inferred 1899 M=6.4 (Abe, 1988), 1918 M=6.8 (Ellsworth, 1990) rupture just north of Anza and the north end of the 1968 Borrego Mountain M=6.8 surface rupture (Figure 6). They used a slip rate of 11 mm/yr, a recurrence interval of 142 years, and assumed the previous event in this segment was 1892. Based on this information a probability of 0.3 was assigned for a magnitude 7 earthquake in the Anza area in the next 30 years.

Figure 6. Seismicity in the southern California region since 1981 with Ml > 1.5. Major earthquakes with observed or inferred offsets are shown with blue arrows. The red arrows designate the two major slip deficits in southern California, 3 meters for the Anza gap on the San Jacinto fault and 6 meters for the Coachella segment of the San Andreas fault. Earthquakes of magnitudes 7+ and 8+ respectively are required to eliminate these slip deficits.

Recently, the Southern California Earthquake Center presented its Phase II report which reassesses the results of the 1988 report. Using the results of Klinger and Rockwell (1989) and Rockwell et al. (1990), the Anza segment of the San Jacinto fault zone is considered by the Working Group on California Earthquake Probabilities (1995) to be the entire 90 km long Clark fault with an average repeat time for a magnitude 7.0 to 7.5 to be 250 (+321, -145) years. Because the dimension of the segment increased, the characteristic slip is now 3.0 m (Figure 6).

The most significant recent information to be developed for the seismic potential of the Anza segment is the 1750 date for the last major earthquake. Using the 142 year recurrence interval of the 1988 report a magnitude 7 earthquake is now 100 years overdue. If one prefers the Phase II report then the characteristic earthquake can be a magnitude 7.5 with the peak in the conditional probability distribution in the year 2000. In either scenario, the characteristic earthquake can generate significant damage in the major population areas of San Diego (90 km distant), the San Bernardino Valley (60 km), and the Los Angeles basin (90-150 km) (Figure 2). In similar situations, significant damage was caused in San Francisco at 120 km distance by the magnitude 6.9 1989 Loma Prieta and in various parts of the Los Angeles basin by the magnitude 6.7 1994 Northridge earthquake over 100 km from the source.

Seismicity Recorded by the ANZA Network

Since the installation of the ANZA network in 1982, there have been nine earthquakes in southern California with magnitudes 6.0 or greater. The ANZA network recorded eight of these mainshocks, the exception being the 1986 Mw = 6.2 North Palm Springs event (Figure 7). Numerous aftershocks from each of these events were recorded on scale and in the cases of the 1987 Elmore Ranch and Superstition Hills events, the 1992 Landers and Joshua Tree earthquakes, and the 1999 Hector Mine earthquake, foreshocks were recorded as well.

Figure 7. All earthquakes with magnitudes greater than 1.9 recorded on the ANZA network.

The evolution of the ANZA network instrumentation has greatly increased the quality of the data from regional and teleseismic events. During the 1992 Joshua Tree-Landers-Big Bear sequence, when the ANZA stations used short-period sensors with 16-bit dynamic range, only the events with magnitudes less than 5.5 were unclipped. After the 1993 upgrade to broadband sensors with 24-bit dynamic range, the 17 January 1994, Mw = 6.8, Northridge earthquake was recorded on-scale. However the 16 October 1999, Mw 7.1, Hector Mine clipped all stations after the S wave arrivals. Another interesting example of the broadband capability for recording teleseismic events by the ANZA network is shown in Figure 8 for the 4 May 2000, Ms= 7.4, Sulawesi, Indonesia earthquake which occurred at a distance of 114°. For comparison, an example of a local Ml = 4.9 is shown in Figure 9.

Figure 8. On-scale broadband recordings of the M=7.4 4 May 2000 Sulawesi, Indonesia earthquake recorded by the ANZA network. The coherent arrivals from this earthquake are a striking example of how the ANZA network can be used as a teleseismic broadband array.

 

Figure 9. Broadband recordings a local Anza M=4.9 26 July 1997 earthquake recorded by the ANZA network

Smaller earthquakes along the San Jacinto fault zone have a strong tendency to occur in one of four clusters of activity (Figure 10). These clusters have in general been persistent seismic features of the entire eighteen-year operational period, but with systematic variations within clusters. The Cahuilla cluster, which is ~ 15 km west of the trace of the San Jacinto fault, has shallow seismicity, less than 6 km from the surface. The Hot Springs cluster at the north end of the array lies between the mapped traces of the Hot Springs faults at depths of 15 to 22 km. The Table Mountain/Toro Peak cluster is a more diffuse zone of seismicity that spans the trifurcation of the San Jacinto fault into the Buck Ridge and Coyote Creek faults, and the seismicity ranges from about 7 to 17 km deep. There are a few events along the trace of the San Jacinto, e.g., a smaller cluster right beneath the town of Anza; however, the dominant pattern of activity lies off the main trace of the fault. Each of these clusters has produced at least one magnitude 4 event during the operational period of the ANZA network.

Research Results Based on ANZA Data

Data and data products from the ANZA network are used by students and researchers at UCSD and other academic institutions (Appendix B).

Fault Zone Trapped Waves

Recently, Li, et al. (1997) showed fault-zone guided waves recorded at the seismic arrays deployed above the Hot Springs cluster (Figure 10) in the San Jacinto fault zone (SJFZ) near Anza. Three linear arrays were deployed, two on the Casa Loma strand and one on the Hot Springs strand, observing microearthquakes occurring within the fault zone. The guided wavetrains characterized by relatively large amplitudes and long period following S-waves were observed only when both the stations and events were located within or close to the fault. The amplitude spectra of guided waves showed peaks at frequencies of 4 to 6 Hz, which decreased sharply with distance from the fault.

Figure 10. Local seismicity of all events recorded between 1982 and 2000 in the central region of the ANZA network. The four local clusters of activity, Hot Springs, Cahuilla, Anza, and Toro Peak-Table Mountain are designated by dashed ellipses. The Anza Seismicity Gap first described by Sanders and Kanamori (1984) is shown in the gray box.

We further found that the significant fault-zone guided waves were only recorded at the seismic arrays across the Casa Loma fault (CLF) which is the southern strand of the SJFZ northwest of Anza, but not at the array deployed across the Hot Springs fault (HSF) which is the northern strand of the SJFZ. This suggests that a low-velocity waveguide exists on the southern fault strand, but not at the northern fault strand. The locations of events for which we observed fault-zone guided waves suggest that this waveguide extends about 30 km along the CLF between the towns of Hemet and Anza. Since the deepest event for which we observed fault-zone guided waves at the CLF occurred at the depth of about 18 km, we interpret that the waveguide extends to 18 km depth, which is consistent with the floor of the seismogenic layer in this region. The data also show that the waveguide on the CLF dips northeastward at 75-80° while it becomes nearly vertical in the Anza slip gap.

In a current project, we installed three 350-m-long 12-element seismic arrays in 1999, across the Coyote Creek fault (CCF), Clark Valley fault (CVF), and Buck Ridge fault (BRF) of the San Jacinto fault zone southeast of Anza, California, to record microearthquakes (Vernon and Li, manuscript in preparation). We observed 4-7 Hz fault-zone trapped waves at stations located close to the fault trace for events occurring within the fault zone. The width of the waveguide is 75-100 m on the BRF and CVF, but is ~75 m on the CCF. The low-velocity waveguides on the BRF, CCF, and CVF are similar but narrower to the waveguide on the Casa Loma fault strand northwest of Anza (Li et al., 1997). Trapped waves also reveal that the waveguide on the BRF dips southwestward while the waveguide on the CVF dips northeastward. They merge into a single waveguide at the seismogenic depth, running northward through Anza slip gap. The waveguide on the CCF in Coyote Ridge is nearly vertical. As in the previous trapped wave study, the precise earthquake locations provided by the ANZA network were essential for the interpretations in this study.

Nucleation processes of large earthquakes

ANZA data has been used for detailed examination of foreshocks and mainshocks. Mori (1996) used the high dynamic range of the ANZA network to examine the rupture directivity and slip distribution of the Ml 4.3 foreshock to the 1992 Joshua Tree earthquake. Two recent papers (Ellsworth and Beroza, 1995; Beroza and Ellsworth, 1996) utilized nine events recorded on the ANZA network with magnitudes as low as 3.5 to study the seismic evidence for an earthquake nucleation phase.

Receiver Functions

Lewis et al. (2000) analyzed teleseismic P waves recorded at the Anza broadband stations and compiled in Datascope relational database tables. They selected records from 67 earthquakes with impulsive, high signal-to-noise P waves and used the teleseismic receiver function technique to obtain a profile of the crustal thickness of the eastern Peninsular Ranges batholith. Based on their analysis, the Moho appears to have an unusually steep dip (compared to other studies such as Richards-Dinger and Shearer (1997) and Zhu and Kanamori (2000) beneath the eastern Peninsular Ranges batholith. The results from the study show that the estimated crustal thickness does not correspond to surface topography. Furthermore, the results are incompatible with the Airy compensation mechanism. Lewis et al. (2000) suggest that the thinning of the crust beneath the eastern Peninsular Ranges is a result of significant extension of the lower crust of the Eastern Peninsular Ranges that is related to the rifting of the Salton trough (Figure 11).

Figure 11. Cross section of Moho depth (“+” and “x” symbols indicate depth in kilometers below sea level found using different lower crustal velocities), elevation (solid line; kilometers above sea level), and stations (squares and triangles indicate the TERRAscope and ANZA networks, respectively). Note that Moho depth does not correlate to elevation. Abbreviations: CB, compositional boundary; SJFZ, San Jacinto fault zone.

Long Period P wave polarization

Vera Schulte-Pelkum, a current graduate student at IGPP, used a combination of three-component broadband single station and array data to develop an unambiguous test for the presence of anisotropy in the crust and upper mantle (Schulte-Peckum, et al., 1998). The method is also capable of locating anisotropy in depth, and resolve its magnitude versus spatial extent. The effect we exploited is the difference between the direction of wave vector and particle motion of teleseismic P onsets. The existence of this difference is an unambiguous indicator for anisotropy, and the strong frequency dependence that we observed in the particle motion and wavefront directions can be used to locate and quantify the amount of anisotropy with depth. We found surprisingly large deviations of P wavefront direction from source location azimuths. This has implications especially for regional tomography, since backprojection of travel times along the wrong azimuths could cause a bias of the resulting model.

The results in the comparison between PFO particle motion and ANZA wave vector were for measurements on broadband data. The analysis can be taken a step further by determining the wave vector direction in a range of narrow frequency bands. We applied a range of bandpass filters to the vertical arrivals before performing the cross-correlation for every band, which gives us the change of wave vector direction with frequency. With close inspection, it becomes apparent that pairs of events with a close to 180° difference in backazimuth have near exactly antisymmetric patterns of azimuth deviation over frequency (Figure 12). The event locations and frequency patterns are on the left. On the right, we flipped the sign of the northwestern event’s residuals before plotting them with the southeastern event’s residuals; they coincide nearly exactly. This means that, e.g. at 30 seconds period, the wave vector was turned towards northeast by about 5° for both events, whereas e.g. at 15 seconds, both wavefronts were turned to the southwest by about 12°. The same observation holds for other event pairs that lie 180° apart. This symmetry with backazimuth also suggests that the cause lies on the receiver end, in the upper mantle underneath ANZA, and that it has a fairly simple symmetry.

Figure 12. The results in the comparison between PFO particle motion and ANZA wave vector above are for measurements on broad-band data. It is apparent that pairs of events with a close to 180° difference in backazimuth have near exactly antisymmetric patterns of azimuth deviation over frequency. The event locations and frequency patterns are on the left. On the right, we flipped the sign of the northwestern event’s residuals before plotting them with the southeastern event’s residuals; they coincide nearly exactly.

Microseisms

Vera Schulte-Peckum, in another project, is studying continuous beamforming on noise recorded at the ANZA array. This study reveals that ocean-generated microseisms arrive on discrete azimuths (Schulte-Peckum and Earle, 1999). Transitions into different azimuth modes are triggered by regional swell events. This contradicts the idea that microseisms, in particular the higher amplitude peak at twice the predominant swell frequency, are of pelagic origin and can be used to track storms, as frequently postulated in the literature. The azimuths of primary versus double-frequency microseisms differ owing to separate mechanisms of ocean-land coupling and differences in propagation. Characteristics of land microseisms seem to be dictated by coastal geometry and regional crustal structure, which opens the possibility of studying the mechanisms of coupling as well as path effects on land.

Figure 13 shows an analysis of noise in January 1999, when ocean swell off California shows a predominantly northwesterly azimuth, surprisingly reveals a very stable base azimuth to SSW (1), interrupted by abrupt switches to W during swell events (2). During a particularly quiet day, the peak power azimuth switches to the northern Atlantic (3), accompanied by an increase in coherence and phase velocity. A comparison with records from July showed no seasonal dependence apart from a less frequent occurrence of swell events.

Figure 13. Analysis of noise in January (when ocean swell off California shows a predominantly northwesterly azimuth) surprisingly reveals a very stable base azimuth to SSW (1), interrupted by abrupt switches to W during swell events (2). During a particularly quiet day, the peak power azimuth switches to the northern Atlantic (3).

Project Plan

The ANZA network is one of the best operational seismic networks in the world in terms of performance, data delivery, and technical capabilities. For this reason alone, continued support of this network is justified. UCSD is the primary source for providing near real-time information on seismic events to the San Diego media and community. The scientific arguments for the ANZA project also remain as strong today as they were 18 years ago. The San Jacinto fault zone, with its branches and extensions into the Imperial Valley, remains one of the most active fault zones in California, and the Anza seismic gap thus remains one of the most probable sites for a moderate to major earthquake in the next few years. We are just now accumulating the amount of high quality data necessary to answer critical questions about time variability of seismicity, source mechanisms, and wave velocities. These data are essential to establishing baseline values for analysis of any future premonitory phenomena.

This network provides the highest quality data and data return rate. The ANZA system uses real-time 24-bit broadband telemetry and can easily accommodate three additional strong motion channels, which could be utilized to exploit available bandwidth. Toro Peak, the central telemetry point, is uniquely situated to provide complete coverage for the whole Coachella segment of the San Andreas fault in addition to most of the San Jacinto fault zone. These fault sections pose two of the most prominent seismic hazards in southern California. From an urban hazards viewpoint, the existing ANZA stations and line-of-sight sites available for potential future stations provide coverage for San Diego, Riverside, and Imperial Counties with a combined population of 3.8 million people.

In keeping with the spirit of cooperation which has characterized seismological research at Anza, and consistent with the scientific motivations of the ANZA network since its establishment, we will coordinate our research and operations effort with the parallel work conducted by TriNet seismologists (Dr. Egill Hauksson and Dr. Lucy Jones) and with SCEC. We will continue to provide real-time data to the regional networks: TriNet, the University of Nevada-Reno, UC Berkeley, CICESE; to the national network: USNSN; to a nationwide education outreach program: IU-PEPP; to a data collection center: IRIS DMC; and to any other end user who requests data.

Proposed Operations

The focus of this proposal is directed towards seismic network operations. We intend to continue to monitor regional and local seismicity and to provide on-scale high dynamic range recordings of moderate to large earthquakes. We also plan to continue to develop and improve the state-of-the-art for 24-bit real-time telemetry from remote sites adjacent to potential major earthquakes sources.

We propose the following developments for the ANZA network:

Field Operations

The data acquisition system of the ANZA network has improved considerably since the original network installation in 1982. Our experience in developing seismic networks and arrays based on the design of the ANZA system has directly influenced two upgrades to the ANZA network. In 2001-2004 we propose to continuously operate the following field configuration:

  1. Fourteen 3-component broadband stations.
  2. All stations using Streckeisen STS-2 broadband seismometers.
  3. 24-bit A/D resolution on all broadband channels.
  4. 100-sps data continuous data streams.
  5. 40-sps data continuous data streams.
  6. 1-sps data continuous data streams.
  7. To move BZN and WMC stations to the south and east to enhance the combined broadband coverage of ANZA and the TriNet.

Additions to the ANZA network:

  1. IGPP has decided to provide equipment for new ANZA stations at a rate of one station per year for the next two years. Specific sites have not been determined yet, but the siting plan will be coordinated with the TriNet to provide the most significant enhancement to the broadband coverage for the San Diego region. This is a significant cost-sharing provided by the Cecil H. and Ida M. Green Foundation for Earth Sciences at UCSD.
  2. UC Santa Barbara has recently assumed ownership of the Borrego Valley Downhole Array which has 4 borehole strong motion accelerometers and 2 surface linear strong motion accelerometer arrays. We will work with UCSB to use the ANZA telemetry infrastructure to send data to UCSB and to incorporate selected channels into the ANZA real-time processing.
  3. The ANZA network will incorporate any future real-time strong motion stations providing better coverage for the San Diego region as funding becomes available.

At present the ANZA broadband stations will saturate on any event inside the array which has M > 5. This limitation also was clearly apparent for large off-array events during the Landers sequence where all events M > 6.0 saturated. This was also true for the Hector Mine mainshock. These large local events would provide essential data to the scientific and engineering community if they are recorded on-scale. The current dataloggers have the capability to record additional three channels which can be used to record strong motion sensors. With data compression, all microwave telemetry links have enough bandwidth to accommodate these extra data. We are not asking for funds under this proposal to implement this option, however we will attempt to generate the necessary funds from internal Institute resources and private sector support during the duration of this proposal.

Data Processing

From 1 October 1982 through 27 May 2000, the catalog includes waveforms and associated parameters from more than 32,000 earthquakes. We use an on-line Datascope database to store all source and waveform parameters along with pointers to easily access the waveform data.

During the period of this proposal we plan to accomplish the following:

  1. Continue real-time transmission of complete ANZA waveform data via Internet to TriNet.
  2. Continue to keep a complete and concurrent archive of the ANZA waveform data at the IRIS DMC in real-time.
  3. Determine routine locations and source parameters for all events and store the results in the Datascope relational database.
  4. Archive all new ANZA waveforms on a RAID mass storage system and provide Internet access to this data.
  5. Develop software for easier access to earthquake source and waveform parameters in Datascope relational database.
  6. Provide timely updates of network response information by providing dataless seed volumes to the IRIS DMC and other users.
  7. Add autodrm capability for accessing ANZA data.

Education and Outreach

During the period of this proposal we plan to accomplish the following:

  1. Provide information, updates, and answers concerning seismological events and issues to the media, general public, and local authorities of the greater San Diego area.
  2. Continue to provide real-time data to the Indiana University — PEPP program and San Diego State University.
  3. Maintain updated maps/web sites showing local seismicity based on real-time catalogs.
  4. After a major event of interest, provide the media and general public with accurate web pages that include web based access to waveforms, maps of event location, source parameters, links to other sites, list of FAQs about the event, and media contact information.
  5. Distribute our web address to relevant search engines.

Reports and Dissemination of Information and Data

The complete waveform data set which consists of over 32,000 events is stored on-line on a RAID mass storage. This data is stored in the standard CSS 3.0 format complete with instrument responses and is accessible over the Internet. A data request is satisfied by placing the data in our anonymous FTP directory for retrieval via the Internet or by sending a tape copy. At present we can provide data in the following formats: CSS 3.0, SAC, or SEED. The IRIS Data Management Center is maintaining a copy of our data archive which is updated on a daily basis.

We are currently developing a world-wide-web home-page for the ANZA network, http://eqinfo.ucsd.edu, which provides maps and information about our database, stations, hardware configurations. In the future it will be possible to display ANZA waveforms through this interface and we plan to provide interactive access to the waveform database.

The primary users of our data and results will be the general public and San Diego based media through our www homepage, our education and outreach real-time seismic displays in IGPP, at the Stephan Birch Aquarium at the Scripps Institution of Oceanography, and at San Diego State University. Additionally, researchers from academia and industry have complete access to all ANZA data and results directly through UCSD or can access data through the SCEC Datacenter or the IRIS DMC.

Related Efforts

The major coordination effort is with TriNet. We are delivering all the ANZA network data in real-time so that the ANZA data can be combined with all the TriNet data to produce earthquake locations and magnitudes based on both datasets. To minimize confusion, the TriNet will maintain a master catalog which they will submit to the composite earthquake catalog of the Council of the National Seismic System. We are also working with the TriNet to coordinate relocating two ANZA stations to improve the broadband coverage in San Diego, Riverside, and Imperial Counties. As new equipment becomes available, we will coordinate new station deployments to optimize the broadband coverage for southern California.

The ANZA network will continue to provide real-time data to San Diego State University for use in their educational program and media presentations.

The continuing operation of the ANZA Seismic Network is important to our Institute in several ways. Firstly, it provides a mechanism to have a real-time view of the local regional and teleseismic seismicity. This is important for our interactions with the San Diego news media when large earthquakes occur and in other situations where public information is needed. San Diego is the 6th largest city in the United States. Secondly, the network is important as an educational tool. Four PhDs at IGPP have been based on ANZA data as well as at least two from other universities. At present, we have one graduate student who is using ANZA data in her thesis work. More than ten undergraduate students have participated in data processing and data analysis over the years and several of those currently work in earthquake research or engineering. Finally, the ANZA model has spawned several projects, including the IRIS Kyrgyz National Network and the IRIS PASSCAL broadband arrays which are currently operating in Montana. In turn, the ANZA project directly benefits from these other projects since the developments made for these additional systems are reincorporated into the ANZA system.

Project Personnel

Curriculum Vitae: Frank L. Vernon III

Institute of Geophysics and Planetary Physics
Scripps Institute of Oceanography, MC 0225
University of California, San Diego
La Jolla, CA 92093, USA

Telephone: (858) 534-5537
Fax: (858) 534-6354
E-Mail: flvernon@ucsd.edu

Education:

Ph.D., Earth Sciences, Scripps Institute of Oceanography, UCSD, 1989
Dissertation: “Analysis of Data Recorded on the ANZA Seismic Network”
B.A., Physics, UCSD, 1977

Employment History:

  • 1977 – Present UCSD, Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography
  • 1996-Present Associate Research Geophysicist
  • 1990-1996 Assistant Research Geophysicist
  • 1989-1990 Postgraduate Research Geophysicist
  • 1980-1989 Staff Research Associate
  • 1977-1980 Development Technician

Professional Experience:

Presently Project Manager of the Seismic Array Program at UCSD IGPP. This program consists of (1) an instrumentation group, (2) a data processing group, and (3) a research component including Dr. Vladik Martinov, visiting scientist from the Institute of Physics of the Earth, Russian Academy of Sciences, one post-doctoral researcher, one graduate student and one undergraduate student.

Principal Investigator

  • ANZA Seismic Network
  • IRIS/PASSCAL Broadband Array
  • Kyrgyz Seismic Network

Bibliography

  • Lewis, J. L., S. M. Day, H. Magistrale, J. Eakins, F. Vernon (2000). Regional crustal thickness variations of the Peninsular Ranges, southern California. Geology. 28, 303-306.
  • Vernon, F. L., G. Pavlis, T. Owens, D. McNamara, and P. Anderson (1998). Near surface scattering effects observed with a high-frequency phased array at Pinyon Flats, California. Bull. Seismol. Soc. Amer., 88, 1548-1560.
  • Li, Y. G., F. L. Vernon, and K. Aki (1997). San Jacinto fault-zone guided waves: A discrimination for recent active strands near Anza, California. J. Geophys. Res., 102, 11689-11702.
  • Pavlis, G. L., D. Repin, S. Radzevicius, F. Vernon (1996). Near-Surface Effects on High-Frequency Seismic Waves: Observations from Dense, Three-Component Seismic Arrays. Proceedings – 18 Annual Seismic Research Symposium. 18, 251-260.
  • Ichinose G, S. Day, H. Magistrale, T. Prush, F. Vernon, A. Edelman (1996). Crustal Thickness Variations Beneath The Peninsular Ranges, Southern California. Geo. Res. Lett., 23, 3095-3098.
  • Al-Shurki, H., G. L. Pavlis, F. L. Vernon (1995). Site Effect Observations from Broadband Arrays Bull. Seismol. Soc. Amer. 85, 1758-1769.

Institutional Qualifications

There are substantial resources in equipment and personnel available at IGPP and UCSD which are available for this project. We have a network of Sun and HP workstations and mass storage devices including hard disks, a 350 Gbyte RAID mass storage device and a 2.5 terabyte Metrum mass storage device, and Exabyte, DAT, and DLT tape readers. There are many seismologists at IGPP who are experienced at processing and manipulating large seismic data sets, and we have considerable software designed for this purpose including the Antelope Software Package developed by Boulder Real-Time Technologies.

Project Management Plan

We request one month per year support for the Principle Investigator F. Vernon who is responsible for the operation of the ANZA network and has extensive experience in working with ANZA data since its installation in 1982. He is involved with the data processing and field operations. Three months of support per year are requested for J. Eakins who is responsible for all aspects of data management, Web pages, and public outreach. Two months of support per year are requested for G. Offield who is responsible for field work and network maintenance. Ten percent per year is requested for research project assistant to provide support involving management of the Toro Peak lease agreement and arrangement of reservations for helicopter services and vehicle rentals and project specific purchasing. We are requesting travel support to enhance the cooperative aspects of this research with members of the USGS at Pasadena.

ANZA Bibliography 1995-Present

  • Al-Shurki, H., G. L. Pavlis, F. L. Vernon (1995). Site Effect Observations from Broadband Arrays Bull. Seismol. Soc. Amer. 85, 1758-1769.
  • Aster, R.C., G. Slad, J. Henton, and M. Antolik (1996). Differential analysis of coda Q using similar microearthquakes in seismic gaps; Part 1, Techniques and application to seismograms recorded in the Anza seismic gap, Bull. Seismol. Soc. Am., 86, 868-889.
  • Beroza, G. C., W. Ellsworth (1996). Properties of the seismic nucleation phase, Tectonophysics, 261, 209-227.
  • Benz, H. M., A. Frankel, D. M. Boore (1997). Regional Lg Attenuation for the Continental United States, Bull. Seismol. Soc. Am., 87, 606-619.
  • Ellsworth, W.L., Beroza, G.C. (1995). Seismic evidence for an earthquake nucleation phase. Science, 268, 851-5.
  • Haase, J.S., P. M. Shearer and R.C. Aster (1995). Constraints on temporal variations in velocity near Anza, California, from analysis of similar event pairs, Bull. Seismol. Soc. Am., 85, 194-206.
  • Ichinose G, S. Day, H. Magistrale, T. Prush, F. Vernon, A. Edelman (1996). Crustal Thickness Variations Beneath The Peninsular Ranges, Southern California. Geo. Res. Lett., 23, 3095-3098.
  • Lewis, J.L., S.M. Day, H. Magistrale, J. Eakins, F. Vernon (2000). Regional crustal thickness variations of the Peninsular Ranges, southern California. Geology, 28, no. 4, 303-306.
  • Li, Y. G., K. Aki, and F. L. Vernon (1997). San Jacinto fault-zone guided waves: A discrimination for recent active strands near Anza, California. J. Geophys. Res., 102, 11689-11702.
  • Li, Y.-G., F. L. Vernon (2000). Fault-zone Trapped Waves at the San Jacinto Fault Zone Southeast of Anza, California. Seis. Res. Lett. 71, 258.
  • Li, Y. G., F. L. Vernon, and K. Aki (1997). Correction to “San Jacinto fault-zone guided waves: A discrimation for recent active strands near Anza, California”. J. Geophys. Res., 102, 20437.
  • Lin, C.H., S. W. Roecker (1996). P-wave backazimuth anomalies observed by a small-aperture seismic array at Pinyon Flat, Southern California; implications for structure and source location?, Bull. Seismol. Soc. Am., 86, 470-476.
  • Mori, J. (1996). Rupture directivity and slip distribution of the M 4.3 foreshock to 1992 Joshua Tree earthquake, Southern California Bull. Seismol. Soc. Am., 86, 805-810.
  • Pavlis, G. L., D. Repin, S. Radzevicius, F. Vernon (1996). Near-Surface Effects on High-Frequency Seismic Waves: Observations from Dense, Three-Component Seismic Arrays. Proceedings – 18 Annual Seismic Research Symposium. 18, 251-260.
  • Steidl, J. H., A. G. Tumarkin and R. J. Archuleta (1996). What is a Reference Site?, Bull. Seismol. Soc. Am., 86, 1733-1748.
  • Zhu, L., H. Kanamori (2000). Moho depth variation in southern Califronia from teleseismic receiver functions. J. Geophys. Res.,105, 2969-2980.

References

  • Abe (1988). Magnitudes and Origin Times From Milne Seismograph Data; Earthquakes in China and California,1898-1912 In: Lee, W.H.K., ed. Historical Seismograms and Earthquakes of the World. Acad. Press: San Diego, CA., 1988, 37-50.
  • Ellsworth, W.L. (1990). Earthquake history, 1769-1989, U.S.G.S. Open File Report 1515.
  • Harvey, D., D. Quinlan, F. Vernon, R. Hansen (1998). ORB: A New Real-Time Data Exchange and Seismic Processing System. Seis. Res. Lett. 69, 165.
  • Klinger, R. E., and T. K. Rockwell (1989). Recurrent late Holocene Faulting at Hog Lake in the Anza seismic gap, San Jacinto fault zone, Southern California GSA, Cord. Sect., Abs., 42, 102.
  • Pavlis, G. L. and F. L. Vernon (1998). Digital communications: The glue linking regional networks and IRIS-PASSCAL. EOS Trans. AGU 79, F560.
  • Richards-Dinger, K.B. and P.M. Shearer (1997). Estiating Crustal Thickness in Southern California by Stacking PmP arrivals, J. Geophys. Res., 102, 15211-15224.
  • Rockwell, T., C. Loughman, and P. Merifield (1990). Late Quaternery Rate of Slip Along the San Jacinto Fault Zone Near Anza, Southern California, J. Geophys. Res., 95, 8593-8606.
  • Sanders, C.O., and H. Kanamori (1984). A seismotectonic analysis of the Anza seismic gap, San Jacinto fault zone, southern California, J. Geophys. Res., 89, 5873-5890.
  • Schulte-Peckum, V. , P. Earle (1999). Azimuthal Variations in Partical Motion, Travel Time and Phase Velocity, EOS, 80, 683.
  • Schulte-Pelkum, V., G. Masters, F. Vernon, G. L. Pavlis (1998). P-Wave Particle Motion, Wavefront Direction, and Anisotropy. EOS Trans. AGU 79, F645.
  • Scott, J.S. (1992). Microearthquake studies in the Anza seismic gap, Ph. D. Thesis, U.C. San Diego.
  • Sharp, R.V. (1967). San Jacinto fault zone in the Peninsular ranges of southern California, Geol. Soc. Am. Bull., 78, 705-730.
  • Thatcher, W., J.A. Hileman, and T. C. Hanks (1975). Seismic slip distribution along the San Jacinto fault zone, southern California, and its implications, Geol. Soc. Amer. Bull., 86, 1140-1146.
  • Vernon III, F.L. (1989). Analysis of data recorded on the ANZA seismic network, Ph. D. Thesis, U.C. San Diego.
  • Vernon, F., T. Wallace (1999). Virtual Seismic Networks. IRIS Newsletter, 18, 7-8.
  • Working Group on Caliornia Earthquake Probablities (1995). Seismic Hazards in Southern California: Probable Earthquakes, 1994 to 2024, Bull. Seismol. Soc. Am., 85, 379-439.
  • Working Group on Caliornia Earthquake Probablities (1988). Probabilities of Large Earthquakes Occurring in California on the San Andreas Fault. USGS, openfile report, 88-398, 62pp.

Current and Pending Support

Current:

  • Collaborative Research: Geodynamics of Intracontinental Mountain Building in the Tien Shan, Central Asia NSF $378,364 4/1/99 — 3/31/02 2 man-months
  • Analysis of Broadband Seismic Measurements from the Ocean Seismic Network Pilot Experiment (w/J. Orcutt) NSF $47,114 2/1/99 — 2/28/01 3 man-months
  • Resolving Anisotropy and Heterogeneity with P Waveforms (w/G. Masters), NSF $150,283 — 7/1/99 – 16/30/01 1 man-month

Pending:

  • UCSD Broadband Array IRIS $268,600 7/1/00 — 6/30/01 4 man-months
  • Collaborative Research: Seismic Catalogue Completeness and Accuracy (w/ T. Wallace of Univ. of AZ and G. Pavlis of Indiana Univ.) DTRA $394,964 4/1/00 — 3/31/03 3 man-months
  • An Interdiscplinary Collaboration on Performance Aspects of a High Performance Wireless Research and Education Network (w/H.W. Braun of the San Diego Computer Center) NSF $2,300,231 7/1/00 — 6/30/03 2.4 man-months
  • Hawaii Ocean Borehole Observatory (HOBO) Collaborative with WHOI (w/J. Orcutt)
    NSF $616,136 10/1/00 — 9/30/01 2.8 man-months
  • Collaborative Research: Crust Mantle Interactions During Continental Growth and High Pressure Rock Exhumation at an Oblique Arc-Continent Collision Zone: The SE Caribbean Margin. (w/ A. Levander of Rice University and T. Wallace of Univ. of AZ)
    NSF $260,047 4/1/01 — 3/31/04 1 man-month
  • Anza Broadband Seismic Network (this proposal) USGS $353,471
    2/1/01 — 1/31/04 1 man-month

Continuation Projects

This proposal is submitted as a continuation of USGS award HQ98AG01940 which previous years funding has been as follows:

Funding Duration Man-Months committed by PI

$75,000 2/1/98 — 1/31/99 1.25
$94,992 2/1/99 — 1/31/00 0.8
$96,673 2/1/00 — 1/31/01 0.8

Appendix A

Statistics from San Diego County

Appendix B

Data Requested through the IRIS DMC

The following image reflects the latest real-time data collected by the ANZA network in Southern California. View an interactive map of recent earthquakes in Southern California. Time is in UTC. What does this image show?

Personnel at IGPP have been responsible for the collection and distribution of seismic data from several regional networks, small aperture arrays, and portable instrument deployments. We maintain local archives of all data collected and distribute the data through the IRIS-DMC. We are part of the ANSS and recieve financial support from the USGS. We are associated with NEHRP.

Broadband Seismic Data Collection Center (ANZA)

Detailed information and research results are available for all of the networks we currently operate, or have installed in the past.

 

 

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Resources:

Homeowners – Earthquake Insurance – Quality Claims

Broadband Seismic Data Collection Center (ANZA)

ANZA network – Broadband Seismic Data Collection Center

Southern California Earthquake Data Center at Caltech

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