Routine analysis of the data produced by BSL networks begins as the waveforms are acquired by computers at UC Berkeley, and ranges from automatic processing for earthquake response to analyst review for earthquake catalogs and quality control.
In the mid 1990s, the BSL developed an automated earthquake notification system (Gee et al., 1996; 2003a) called Rapid Earthquake Data Integration (REDI). This system determined earthquake parameters rapidly, producing near real-time locations and magnitudes of Northern and Central California earthquakes, estimates of the rupture characteristics and the distribution of ground shaking following significant earthquakes, and tools for the rapid assessment of damage and estimation of loss. Then, in 1996, a collaboration began between the BSL and the USGS for reporting on Northern and Central California earthquakes. Programs in Menlo Park and Berkeley were merged into a single earthquake notification system using data from the NCSN and the BDSN. The USGS and the BSL now form the Northern California Earthquake Management Center (NCEMC) of the California Integrated Seismic Network (Section 2). In the most recent step of a long cooperative integration process, the CISN software became the production software for earthquake reporting in the NCEMC in June 2009.
With partial support from the USGS, the BSL is also participating in the development and assessment of a statewide prototype system for warning of imminent ground shaking in the seconds after an earthquake has initiated but before strong motion begins at sites that may be damaged. (See Research Study 17.)
In this section, we describe how the Northern California Earthquake Management Center fits within the CISN system. Figure 3.9 in Section 2 illustrates the NCEMC as part of the the CISN communications ring. The NCEMC is a distributed center, with elements in Berkeley and in Menlo Park. The 35 mile separation between these two centers is in sharp contrast to the Southern California Earthquake Management Center, where the USGS Pasadena is located across the street from the Caltech Seismological Laboratory. As described in Section 2, the CISN partners are connected by a dedicated T1 communications link, with the capability of falling back to the Internet. In addition to the CISN ring, the BSL and the USGS Menlo Park have a second dedicated communications link to provide bandwidth for shipping waveform data and other information between their processing systems.
Figure 3.27 provides more detail on the system operating at the NCEMC since mid-June, 2009. Now, complete earthquake information processing systems operate in parallel in Menlo Park and Berkeley. Incoming data from each network is processed locally at the two data centers in the network services computers. The continuous reduced data, which include picks, codas, ground motion amplitudes and ML100, are exchanged between the data centers and fed into both processing streams. Real time analysis is coordinated using up-to-date information from the local real time database, which is replicated to the local data center database. Event review and automatic downstream processes such as computation of fault plane solutions access the internal data center databases. To maintain redundancy, robustness, and completeness, these two databases replicate each other across the Bay. They also replicate with the public database, from which information is made available to the outside. The system includes the production of location and origin time as well as estimates of , , and . For events with ShakeMaps are also calculated on two systems, one in Menlo Park and one in Berkeley. Finite fault calculation is not yet integrated into the new processing system. It is only calculated at the BSL at this time.
This new system combines the advantages of the NCSN with those of the BDSN. The dense network of the NCSN provides rapid and accurate earthquake locations, low magnitude detection thresholds, and first-motion mechanisms. The high dynamic range data loggers, digital telemetry, and broadband and strong-motion sensors of the BDSN provide reliable magnitude determination, moment tensor estimation, calculation of peak ground motions, and estimation of source rupture characteristics. With the advent of the new system, we have lost the capability of publishing robust preliminary hypocenters, or ``Quick Looks'' within about 25 seconds after the origin time, but we are working to reestablish it. Thus, locations are now published when preliminary coda magnitudes are available, within 2-4 minutes of the origin time. Estimates of local magnitude are generally available 30-120 seconds later, and other parameters, such as the peak ground acceleration and moment magnitude, follow within 1-4 minutes (Figure 3.28).
Earthquake information is now distributed to the web through EIDS and is available through the USGS Earthquake Notification Service https://sslearthquake.usgs.gov/ens/. Organizations with the need for more rapid earthquake information should use CISN Display http://www.cisn.org/software/cisndisplay.htm. The recenteqs site has enjoyed enormous popularity since its introduction and provides a valuable resource for information which is useful not only in the seconds immediately after an earthquake, but in the following hours and days as well.
During the last few years, BSL staff members, particularly Pete Lombard, have become extremely familiar with elements of the TriNet software. The software is now adapted for Northern California, with many adjustments and modifications completed along the way. For example, Pete Lombard adapted the TriNet magnitude module to Northern California. Pete made a number of suggestions on how to improve the performance of the magnitude module and has worked closely with Caltech and the USGS/Pasadena on modifications.
The BSL and the USGS Menlo Park have implemented a system to exchange ``reduced amplitude timeseries." One of the important innovations of the TriNet software development is the concept of continuous processing (Kanamori et al., 1999). Waveform data are constantly processed to produce Wood Anderson synthetic amplitudes and peak ground motions. A program called rad produces a reduced timeseries, sampled every 5 seconds, and stores it in a memory area called an ``Amplitude Data Area" or ADA. Other modules can access the ADA to retrieve amplitudes to calculate magnitude and ShakeMaps as needed. The BSL and the USGS Menlo Park have collaborated to establish tools for ADA-based exchange. As part of the software development in Northern California, a number of modules have been developed.
The BSL continues to focus on the unique contributions that can be made from the broadband network, including moment tensor solutions and finite fault analysis. Caltech developed a Java and web-based moment tensor processing system and review interface for the complete waveform modeling technique of Dreger and Romanowicz (1994). The web-based review interface was upgraded during 2007 to include new mechanism-related tables, and has been used in Northern California since July 2007. During the first six months of 2009, the automatically running version for real time analysis was extensively tested and updated by Pete Lombard, with updates made to the review interface as well. With the transition to the new software, automatic moment tensor analysis now proceeds through the tmts system. At the same time, we changed our reporting rules so that automatically produced solutions of high quality are now published to the web.
From July 2008 through June 2009, BSL analysts reviewed many earthquakes in Northern California and adjoining areas of magnitude 3.2 and higher. Reviewed moment tensor solutions were obtained for 56 of these events (through 6/30/2009). Figure 3.30 and Table 3.14 display the locations of earthquakes in the BSL moment tensor catalog and their mechanisms. During this year, no earthquakes were large enough to allow finite fault inversions to be performed.
With the transition to the new software, local magnitudes are no longer calculated with the REDI code. As part of the transition to the new software, we worked with Southern California to develop a statewide procedure for calculating . A new log function was been developed that is valid throughout the state, and a corresponding set of corrections calculated for the collocated broadband and strong motion stations. Southern California began using these paramaters in early 2008, and they are now being used in Northern California as well. determinations by Southern and Northern California with their respective stations for a sequence of events south of Bishop compare very well.
In fiscal year 2008-2009, more than 21,500 earthquakes were detected and located by the automatic systems in Northern California. This compares with over 26,000 in 2007-2008, 23,000 in 2006-2007, 30,000 in 2005-2006 and 38,800 in 2004-2005. Many of the large number of events in 2004-2005 are aftershocks of the 2003 San Simeon and 2004 Parkfield earthquakes. Of the more than 21,500 events, about 140 had preliminary magnitudes of three or greater. Thirteen events had greater than 4. The largest event recorded by the system occurred off the coast of Cape Mendocino on 28 October 2008. It had 4.9.
Although BSL staff are no longer reading BDSN records for local and regional earthquakes (see Annual Report of 2003-2004), they are now participating in timing and reviewing earthquakes with Jiggle, mainly working on events from past sequences that have not yet been timed. This work contributes to improving the earthquake catalog for Northern California, but also ensures robust response capabilities, should the Menlo Park campus be disabled for some reason.
Peggy Hellweg oversees our earthquake monitoring system and directs the routine analysis. Peter Lombard and Doug Neuhauser contribute to the development of software. Rick McKenzie, Taka'aki Taira, Doug Dreger, Holly Brown, Shan Dou, Sean Ford, Kelly Grijalva, Aurelie Guilhem, Ahyi Kim, Ved Lekic, Rob Porritt, Jennifer Taggart, Amanda Thomas, and Gilead Wurman contribute to the routine analysis of moment tensors. Peggy Hellweg, Doug Neuhauser, and Bob Uhrhammer contributed to the writing of this section. Partial support for the development and maintenance of the REDI system is provided by the USGS.
Dreger, D., and B. Romanowicz, Source characteristics of events in the San Francisco Bay region, USGS Open File Report 94-176, 301-309, 1994.
Gee, L., J. Polet, R. Uhrhammer, and K. Hutton, Earthquake Magnitudes in California, Seism. Res. Lett., 75(2), 272, 2004.
Gee, L., D. Neuhauser, D. Dreger, M. Pasyanos, R. Uhrhammer, and B. Romanowicz, The Rapid Earthquake Data Integration Project, Handbook of Earthquake and Engineering Seismology, IASPEI, 1261-1273, 2003a.
Gee, L., D. Dreger, G. Wurman, Y, Gung, B. Uhrhammer, and B. Romanowicz, A Decade of Regional Moment Tensor Analysis at UC Berkeley, Eos Trans. AGU, 84(46) , Fall Meet. Suppl., Abstract S52C-0148, 2003b.
Gee, L., D. Neuhauser, D. Dreger, M. Pasyanos, B. Romanowicz, and R. Uhrhammer, The Rapid Earthquake Data Integration System, Bull. Seis. Soc. Am., 86, 936-945, 1996.
Pasyanos, M., D. Dreger, and B. Romanowicz, Toward real-time estimation of regional moment tensors, Bull. Seis. Soc. Am., 86, 1255-1269, 1996.
Romanowicz, B., D. Dreger, M. Pasyanos, and R. Uhrhammer, Monitoring of strain release in central and northern California using broadband data, Geophys. Res. Lett., 20, 1643-1646, 1993.
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