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.
Over the last 10 years, the BSL has invested in the development of the hardware and software necessary for an automated earthquake notification system (Gee et al., 2003; Gee et al., 1996). The Rapid Earthquake Data Integration (REDI) project is a research program at the BSL for the rapid determination of earthquake parameters with three major objectives: to provide near real-time locations and magnitudes of northern and central California earthquakes; to provide estimates of the rupture characteristics and the distribution of ground shaking following significant earthquakes, and to develop better tools for the rapid assessment of damage and estimation of loss. A long-term goal of the project is the development of a system to warn of imminent ground shaking in the seconds after an earthquake has initiated but before strong motions begin at sites that may be damaged.
In 1996, the BSL and USGS began collaboration on a joint notification system for northern and central California earthquakes. The current system merges the programs in Menlo Park and Berkeley into a single earthquake notification system, combining data from the NCSN and the BDSN.
Today, the BSL and USGS system forms the Northern California Management Center (NCMC) of the California Integrated Seismic Network (Chapter 2).
The details of the Northern California processing system and the REDI project have been described in past annual reports. In this section, we will describe how the Northern California Management Center fits within the CISN system, detail recent developments, and discuss plans for the future development.
Figure 10.1 illustrates the NCMC as part of the the CISN communications ring. The NCMC is a distributed center, with elements in Berkeley and Menlo Park. The 35 mile separation between these two centers is in sharp contrast to the Southern California Management Center, where the USGS Pasadena is located across the street from the Caltech Seismological Laboratory. As described in Chapter 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 communication link to provide bandwidth for shipping waveform data and other information between their processing systems.
Figure 10.2 provides more detail on the current system at the NCMC. At present, two Earthworm-Earlybird systems in Menlo Park feed two "standard" REDI processing systems at UC Berkeley. One of these systems is the production or paging system; the other is set up as a hot backup. The second system is frequently used to test new software developments before migrating them to the production environment. The Earthworm-Earlybird-REDI systems perform the standard detection, location, estimation of , , and , as well as processing of ground motion data. The computation of ShakeMaps is also performed on two systems, one in Menlo Park and one in Berkeley, as described below. An additional system performs finite-fault processing and the computation of higher level ShakeMaps.
The dense network and Earthworm-Earlybird processing environment of the NCSN provides rapid and accurate earthquake locations, low magnitude detection thresholds, and first-motion mechanisms for smaller quakes. The high dynamic range data loggers, digital telemetry, and broadband and strong-motion sensors of the BDSN and REDI analysis software provide reliable magnitude determination, moment tensor estimation, peak ground motions, and source rupture characteristics. Robust preliminary hypocenters are available about 25 seconds after the origin time, while preliminary coda magnitudes follow within 2-4 minutes. 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 10.3).
Earthquake information from the joint notification system is distributed by pager/cellphone, e-mail, and the WWW. The first two mechanisms "push" the information to recipients, while the current Web interface requires interested parties to actively seek the information. Consequently, paging and, to a lesser extent, e-mail are the preferred methods for emergency response notification. The recenteqs site has enjoyed enormous popularity since its introduction and provides a valuable resource for information whose bandwidth exceeds the limits of wireless systems and for access to information which is useful not only in the seconds immediately after an earthquake, but in the following hours and days as well.
The BSL and USGS/Menlo Park staff met in August 2002 to discuss how to improve the robustness of ShakeMap operation in northern California. At that time, ShakeMaps in northern California depended on the operation of a single computer, located in Menlo Park. This was in contrast to other earthquake monitoring operations, where 2 parallel systems provide back-up capability should a computer fail. The BSL and USGS Menlo Park agreed to bring up a second ShakeMap system at UC Berkeley, which will be twin or clone of the Menlo Park system.
The implementation of the second ShakeMap system was completed in early 2003, using one of the new CISN processing computers. Both ShakeMap systems are be driven off the "production" monitoring system and both are configured to allow distribution of ShakeMaps to the Web and to recipients such as OES. At any one time, however, only one system distributes information.
In parallel, Pete Lombard at the BSL was trained to review ShakeMaps following an earthquake. Since early in 2003, the BSL has been trading the responsibility of ShakeMap production. The key to making a ShakeMap machine take over the production duty is to copy the earthquake database file from the former production machine to the new production machine. In that way, both machines can produce consistent ShakeMap archive lists.
The BSL has started work on a system to help with review of ShakeMaps. By modifying the program grind, we now write logs of the PGA and PGV values from station data, the regression curve, and the limits used by grind to flag outlier stations. This data is then plotted on amplitude vs. distance log-log plots. While this simple plot loses the spatial information available from a map view, it accurately reflects the process that grind uses for flagging stations. And the outlying data are more apparent on the x-y plots. For now, our plotting is done by a crude script running gnuplot. We intend at least to change this to use GMT for plotting. And we imagine that some day a pair of "clickable" plots could be presented on an internal Web server for use by ShakeMap reviewers.
The REDI system has routinely produced automatic estimates of moment magnitude () for many years. However, these estimates have not routinely used as the "official" magnitude, due in part to questions about the reliability of the automatic solutions. However, in response to the 05/14/2002 Gilroy earthquake ( 4.9, 5.1) and the complications created by the publication of multiple magnitudes, the BSL and USGS Menlo Park have agreed to use automatically determined moment magnitudes, when available, to supplement estimates of local magnitude (). This work was completed in the last year and is now routinely reported when the solution is "good enough".
When is a solution "good enough"? This question has been under review in the last year - both to ensure reliable reporting of in northern California and as part of the CISN-effort to establish rules for a magnitude hierarchy. Figures 10.4 & 10.5 illustrate a dataset compiled since the most recent modification of the moment tensor software. The dataset indicates that the estimate from the complete waveform inversion is quite robust for when a variance reduction of 40% or higher is obtained. In general, earthquakes of M4.5 and higher almost always achieve that level of variance reduction. Under the current rules, the Northern California Management Center always reports if the variance reduction is 40% or better.
We have also looked at comparisons between our regional estimate of and the moment magnitudes determined by Harvard as part of the Centroid Moment Tensor project. Figure 10.6 illustrates the regional compared with the CMT , along with comparisons between the NEIC estimates of , , and the CMT . This dataset spans approximately 60 events in the western US and good agreement between the regional and global methods is observed, although there appears to be a systematic difference in the estimates of approximately 0.08 - 0.09 magnitude units, with the CMT estimate being higher.
In the last year, the BSL and the USGS Menlo Park completed the software modifications necessary to track version numbers in the processing system. Version numbers are important for identifying the latest (and therefore hopefully the best) hypocenter and magnitude for an earthquake. Because both Menlo Park and Berkeley can be a source of earthquake information, it was critical to design a common versioning system. The modifications enabled the BSL to begin contributing solutions to QDDS, increasing the robustness of data distribution in northern California. At the present time, the USGS Menlo Park distributes solutions to 2 of the 3 QDDS hubs and the BSL distributes solutions to 2 of the 3 hubs (that is, 2 hubs receive notices from either the USGS or the BSL and 1 hub receives notices from both). This implementation should allow information to be distributed in the case of Internet shutdown of the Department of Interior (as occurred in December 2001 - see http://www.cisn.org/news/doi.html).
During the past year, the BSL completed modifications to implement a database within real-time system. At this point, the database is used as a storage system, supplementing the flat files that have been the basis of the REDI system. The modified software has now been installed on both REDI platforms.
Figure 10.2 illustrates the current organization of the two systems. As described above, an Earthworm/Earlybird component is tied to a REDI component and the pair form a single "joint notification system". Although this approach has functioned reasonably well over the last 7 years, there are a number of potential problems associated with the separation of critical system elements by 30 miles of San Francisco Bay.
Recognizing this, we intend to redesign the Northern California operations so that a single independent system operates at the USGS and at UC Berkeley. Figure 10.7 illustrates the planned configuration. In FY01/02, our discussions proceeded to the stage of establishing specifications and determining the details required for design. However, in the last year, most of the development effort focused on CISN activities and specific plans for the "next generation" Northern California system were put on hold. This enforced wait provided the opportunity for some ideas to mature and the current plans for the NCMC are somewhat different from those envisioned in 2001.
The current design draws strongly on the experience in Southern California for the development of TriNet. In the last year, BSL staff, particularly Pete Lombard, have become extremely familiar with portions of the TriNet software. We have begun to adapt the software for Northern California, making adjustments and modifications along the way.
We anticipate that the next generation of Northern California Management Center system will include many elements from the TriNet software. Certain components, such as the dependence on third part software for communication among processing modules, will be modified and an alternative distribution system utilized.
On a daily basis, the BSL continues to locate and determine the magnitude of earthquakes in northern California and adjacent regions. As a general rule, events are analyzed if their magnitude is greater than 2.8 in the Central Coast ranges, greater than 3.0 in all of northern California, or greater than 3.8 in the bordering regions. Traditionally, these events were located using hand-picked arrival times from the BDSN stations in conjunction with P-arrival times from the NCSN using the program st-relp. Over the past several years, the BSL has made a transition in the daily analysis to take advantage of the automatic processing system. As part of this transition, events which have been processed by the automatic system are not generally relocated, although phase arrivals are still hand-picked and the synthetic Wood-Anderson readings are checked. Instead, analysts are focusing on the determination of additional parameters, such as the seismic moment tensor, phase azimuth, and measures of strong ground shaking.
From July 2002 through June 2003, BSL analysts reviewed nearly 150 earthquakes in northern California and adjoining areas, ranging from M2.2 to 6.2. Reviewed moment tensor solutions were obtained for 24 events (through 6/30/2002). Figure 10.8 and Table 10.1 displays the earthquakes located in the BSL catalog and the moment tensor solutions.
In addition to the routine analysis of local and regional earthquakes, the BSL also processes teleseismic earthquakes. Taking advantage of the ANSS catalog, analysts review teleseisms of magnitude 5.8 and higher. All events of magnitude 6 and higher are read on the quietest BDSN station, while events of magnitude 6.5 and higher are read on the quietest station and BKS. Earthquakes of magnitude 7 and higher are read on all BDSN stations.
The locations and magnitude determined by the BSL are cataloged on the NCEDC. The phase and amplitude data are provided to the NEIC, along with the locations and magnitudes, as contributions to the global catalogs, such as that of the ISC.
Lind Gee leads the development of the REDI system and directs the routine analysis. Peter Lombard and Doug Neuhauser contribute to the development of software. Rick McKenzie, Doug Dreger, and Dennise Templeton contribute to the routine analysis. Lind Gee, Doug Neuhauser, and Dennise Templeton contributed to the writing of this chapter.
Partial support for the develop of the REDI system is provided by the USGS.
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, 2003.
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.
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