Northern California Earthquake Monitoring

Introduction

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).

Northern California
Management Center

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 10.1: Schematic diagram illustrating the connectivity between the real-time processing systems at the USGS Menlo Park and UC Berkeley, forming the northern California Management Center, and with other elements of the CISN.
\begin{figure}\begin{center}
\epsfig{file=ncmc.ps, width=8cm}\end{center}\end{figure}

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 $M_{d}$, $M_{L}$, and $M_{w}$, 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.

Figure 10.2: Detailed view of the current Northern California processing system, showing the two Earthworm-Earlybird-REDI systems, the two ShakeMap systems, and the finite-fault system.
\begin{figure}\begin{center}
\epsfig{file=jns.ps, width=8cm, bbllx=54,bblly=233,bburx=570,bbury=690}\end{center}\end{figure}

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.

Figure 10.3: Illustration of the current (solid lines) and planned/proposed (dotted lines) development of real-time processing in northern California. The Finite Fault I and II are fully implemented within the REDI system at UC Berkeley and are integrated with ShakeMap. The resulting maps are still being evaluated and are not currently available to the public.
\begin{figure*}\begin{center}
\epsfig{file=timeline.ps, width=15cm}\end{center}\end{figure*}

2002-2003 Activities

ShakeMap

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.

$M_{w}$

The REDI system has routinely produced automatic estimates of moment magnitude ($M_{w}$) 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 ($M_{w}$ 4.9, $M_{L}$ 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 ($M_{L}$). This work was completed in the last year and $M_{w}$ 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 $M_{w}$ 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 $M_{w}$ 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 $M_{w}$ if the variance reduction is 40% or better.

We have also looked at comparisons between our regional estimate of $M_{w}$ and the moment magnitudes determined by Harvard as part of the Centroid Moment Tensor project. Figure 10.6 illustrates the regional $M_{w}$ compared with the CMT $M_{w}$, along with comparisons between the NEIC estimates of $M_{w}$, $m_{b}$, $M_{s}$ and the CMT $M_{w}$. 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.

Figure 10.4: Left: Left: Comparison of the two regional estimates of moment magnitude - the complete waveform (CW) and the surface wave (SW) methods - from the last year of REDI results and a few older events rerun through the system. As observed in Pasyanos et al., 1996, the estimates of moment from the surface wave inversion are larger than the complete waveform inversion. Right: Comparison of the estimates of $M_{w}$ from automatic and reviewed complete waveform solutions.
\begin{figure*}\begin{center}
\epsfig{file=lsg_ar1,width=10cm, bbllx=25,bblly=25,bburx=575,bbury=510}\end{center}\end{figure*}

Figure 10.5: Results from the last year of complete waveform moment tensor inversions in the REDI system, with a few older events. With one exception, all events of M4.5 and higher achieved a variance reduction of 40%; approximately one third of the smaller events achieved the same level.
\begin{figure}\begin{center}
\epsfig{file=lsg_ar2,width=8cm, bbllx=25,bblly=25,bburx=288,bbury=288}\end{center}\end{figure}

Figure 10.6: Comparison of several magnitudes with the $M_{w}$ estimates determined from the Harvard Centroid Moment Tensor project. Lower left: Regional $M_{w}$ from the reviewed solutions of the BSL; lower right: Global $M_{w}$ from NEIC; upper left: $m_{b}$ from NEIC; upper right: $M_{s}$ from NEIC.
\begin{figure*}\begin{center}
\epsfig{file=lsg_ar3,width=10cm, bbllx=25,bblly=25,bburx=575,bbury=575}\end{center}\end{figure*}

Version Numbers/Quake Data
Delivery System

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).

Database Implementation

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.

System Development

As part of ongoing efforts to improve the monitoring systems in northern California, the BSL and the USGS Menlo Park have begun to plan for the next generation of the northern California joint notification system.

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.

Figure 10.7: Future design of the Northern California Earthquake Notification System. In contrast with the current situation (Figure 10.2), the system is being redesigned to integrate the Earthworm/Earlybird/REDI software into a single package. Parallel systems will be run at the Berkeley and Menlo Park facilities of the Northern California Operations Center.
\begin{figure}\begin{center}
\epsfig{file=ncops_future.ps, width=8cm}\end{center}\end{figure}

Routine Earthquake Analysis

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.

Figure 10.8: Map comparing the reviewed moment tensor solutions determined by the BSL in the last 10 years (blue) and those from the last fiscal year (red).
\begin{figure*}\begin{center}
\epsfig{file=mt_decade.ps,width=15cm,angle=-90,bbllx=10,bblly=50,bburx=590,bbury=760}\end{center}\end{figure*}

Figure 10.9: This map illustrates the Feb 2003 Dublin and Nov 2002 San Ramon swarms in the context of historical seismicity. Earthquakes from the USGS catalog 1970-2003 are plotted, with events of $M_{L}$ >= 4.0 plotted with large circles. Events associated with various sequences are plotted in color: 1970 Danville (blue), 1976 Danville (turquoise), 1980 Livermore (grey), and 1990 Alamo (green). Events from the 2002 swarm are plotted in yellow and the events from 2003 are plotted in red.
\begin{figure*}\begin{center}
\epsfig{file=dublin_annotate.ps,width=17cm,bbllx=59,bblly=140,bburx=570,bbury=650}\end{center}\end{figure*}


Table 10.1: Moment tensor solutions for significant events from July 1, 2001 to June 30, 2002 using the complete waveform fitting method. Epicentral information from the UC Berkeley/USGS Northern California Earthquake Data Center. Moment is in dyne-cm and depth is in km.

Location Date Time Lat. Lon. MT Dep. $M_{L}$ $M_{w}$ $M_{o}$ Str. Dip Rake
Bishop 07/15/2002 20:18:17.0 37.385 -118.407 14.0 4.1 3.7 3.50e21 300 76 -154
Parkfield 09/06/2002 07:28:22.0 35.834 -120.450 14.0 4.0 4.0 9.79e21 321 88 175
San Benito 09/25/2002 07:08:46.0 36.592 -121.199 11.0 3.9 3.8 6.70e21 134 87 176
Pinnacles 09/28/2002 16:07:47.0 36.595 -121.200 14.0 3.7 3.7 4.49e21 146 81 177
Ludlow 10/29/2002 14:16:53.0 34.807 -116.267 8.0 4.9 4.6 7.84e22 356 79 167
Parkfield 11/12/2002 16:48:25.0 35.972 -120.522 11.0 4.2 4.1 1.80e22 141 87 -173
Punta Gorda 11/21/2002 13:17:39.0 40.295 -124.420 11.0 3.5 3.9 8.65e21 104 88 173
San Ramon 11/24/2002 14:54:23.0 37.760 -121.950 8.0 3.9 3.9 7.75e21 242 84 -13
Hollister 01/07/2003 22:29:27.0 36.806 -121.389 11.0 4.7 4.3 3.71e22 147 80 -174
Petrolia 01/08/2003 05:41:43.0 40.422 -125.445 8.0 4.2 4.7 1.12e23 20 79 31
Dublin 02/02/2003 16:22:52.0 37.746 -121.943 14.0 3.6 3.7 4.46e21 259 81 14
Dublin 02/02/2003 18:22:58.0 37.740 -121.937 14.0 4.2 4.1 1.36e22 67 88 -19
Dublin 02/02/2003 18:47:39.0 37.748 -121.942 11.0 4.0 4.1 1.36e22 67 87 -34
Arcata 02/18/2003 14:44:24.0 41.179 -125.237 11.0 3.7 4.2 2.39e22 44 75 3
Big Bear City 02/22/2003 12:19:10.0 34.310 -116.848 5.0 5.4 5.0 3.20e23 40 75 -20
Mammoth Lakes 03/08/2003 15:35:02.0 37.572 -118.885 5.0 4.3 4.1 1.36e22 2 62 -39
Hydesville 04/22/2003 10:46:09.0 40.588 -124.086 27.0 3.9 4.4 3.76e22 40 84 -33
Geysers 05/20/2003 16:50:42.0 38.800 -122.804 5.0 3.6 4.0 1.31e22 346 79 136
Santa Rosa 05/25/2003 00:09:33.0 38.460 -122.700 8.0 4.3 4.2 1.96e22 245 86 4
Petrolia 06/26/2003 03:39:35.4 40.395 -126.574 14.0 4.1 4.6 8.22e22 272 87 -142


Special Events

In late November, a small swarm of earthquakes occurred near the Calaveras fault in San Ramon. The largest event was a $M_{w}$ 3.9 and with 4 events over M3.5. The pre-Thanksgiving events were felt over a large area - the Community Internet Intensity Map reports approximately 2400 responses for the M3.9. The Northern California Management Center put together an Internet report on the sequence and posted it on the CISN Web page: http://www.cisn.org/special/evt.02.11.24/In early February, a small swarm of earthquakes occurred near the Calaveras fault in Dublin. The largest event in this sequence was an $M_{L}$4.2, with 3 events of M3.5. In contrast to the events in November, these events occurred sub parallel to the Calaveras fault (Figure 10.9). As in November, these events were felt over a broad area, although no damage was reported.

Teleseisms

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.

Acknowledgements

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.

References

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.

Berkeley Seismological Laboratory
215 McCone Hall, UC Berkeley, Berkeley, CA 94720-4760
Questions or comments? Send e-mail: www@seismo.berkeley.edu
© 2004, The Regents of the University of California