Routine earthquake analysis in Northern California has been unified since June 2009, with mirrored systems at the BSL and at the USGS in Menlo Park (see Operational Section 2). Processing begins as the waveforms arrive at the computers operating the real-time software, or AQMS software, 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 (Operational Section 2). Since June 2009, the AQMS software is the production software for earthquake reporting in the NCEMC.
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 19.)
In this section, we describe how the Northern California Earthquake Management Center fits within the CISN system. Figure 3.11 in Operational 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 Operational 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 3.32 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 are processed locally at each of the two data centers in 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. Robust preliminary hypocenters, or ``Quick Looks'' are published within about 25 seconds of the origin time. Event information is updated when preliminary coda magnitudes are available, within 2-4 minutes of the origin time. Estimates of local magnitude are generally available 30 seconds later, and other parameters, such as the peak ground acceleration and moment magnitude, follow within 1-4 minutes (Figure 3.33).
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.
Data flow in the new Northern California system (Figure 3.34) has been modified to allow for local differences (such as very different forms of data acquisition and variability in network distribution). In addition, the BSL and the USGS want to minimize use of proprietary software in the system. One exception is the database program, Oracle. The NCEDC Oracle database hosts all earthquake information and parameters associated with the real time monitoring system. It is the centerpoint of the new system, providing up-to-date information to all processing modules. Reliability and robustness are achieved by continuously replicating the databases. The public, read-only, database provides event and parametric information to catalog users and the public.
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 are exchanging ``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. The next step in improving reliability and robustness is to implement ADA exchange with Southern California as well.
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. tmts is a Java and web-based moment tensor processing system and review interface based on the complete waveform modeling technique of Dreger and Romanowicz (1994). The improved, web-based review interface has been operating in Northern California since July 2007. The automatically running version for real time analysis was extensively tested and updated by Pete Lombard, and has been running since June 2009. Reporting rules now allow automatically produced solutions of high quality to be published to the web.
From July 2009 through June 2010, BSL analysts reviewed many earthquakes in Northern California and adjoining areas of magnitude 2.9 and higher. Reviewed moment tensor solutions were obtained for 68 of these events (through 6/30/2010). Figure 3.35 and Table 3.13 display the locations of earthquakes in the BSL moment tensor catalog and their mechanisms. During this year, a finite fault inversion was produced for the January 9, 2010, offshore Ferndale earthquake which had a moment magnitude of 6.5. For a report on the finite fault solution for that event, see Research Section 20.
In fiscal year 2009-2010, more than 25,000 earthquakes were detected and located by the automatic systems in Northern California. This compares with over 21,500 in 2008-2009, 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 25,000 events, about 124 had preliminary magnitudes of three or greater. Fourteen events had or greater than 4. The largest event recorded by the system occurred offshore of Ferndale on 09 January 2010. It had 6.5.
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, Sanne Cottaar, Shan Dou, Kelly Grijalva, Aurelie Guilhem, Ved Lekic, Rob Porritt, Jennifer Taggart, Amanda Thomas, Gilead Wurman, and Zhao Zheng 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, implementation and maintenance of the AQMS software 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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