James Mori (Disaster Prevention Research Institute, Kyoto University)
The deficiencies in our seismic networks for making real contributions toward earthquake hazard reduction were emphasized by the economic losses ($30 billion) in the 1994 Northridge, California earthquake and the large economic losses ($200 billion) and many casualties (over 6000 killed) in the 1995 Kobe, Japan earthquake. Both earthquakes occurred in regions with relatively good seismic monitoring systems, but the instrumental information was lacking in several respects. In the Northridge event, there was extensive damage to a large number of structures, including the well-publicized problem of cracks in the welds of many of the large steel frame buildings (Krawinkler et al.). However, there were relatively few strong-motion recordings to document the actual ground shaking that caused the damage. Kobe had a similar sparseness of strong-motion data, with the additional problem of lack of realtime information that might have facilitated emergency response.
TriNet Goals
The main organizations that record seismic data in southern California
(California Institute of Technology (Caltech), U.S. Geological Survey
(USGS), and the California Division of Mines and Geology (CDMG) of the
Department of Conservation) joined together to form the TriNet project for
implementing major improvements in seismic and strong-motion networks. The
plan is to build an integrated system that begins to meet the needs of
emergency response, engineering concerns in southern California, and the
seismological research community. An ambitious instrumental and system
development project has started to record and disseminate ground motions
from a spatially-dense and robust network of high-quality seismographs in
southern California. The project has three main objectives.
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Instrumentation
The project is divided into two elements with the realtime information
emphasis centered at Caltech/USGS in Pasadena and the extensive collection
of strong-motion data for engineering purposes centered at CDMG in
Sacramento.
By 2002, there will be 670 stations in southern California. Caltech/USGS
will be installing broadband and strong-motion sensors with continuous
telemetry, expanding the efforts started by the USGS to a total of 200 high
dynamic-range sites. CDMG will be installing new sites or upgrading existing
instrumentation to provide digital strong motion recording from 400
stations. Many of the strong-motion instruments will be part of the CDMG
plan for establishing engineering reference sites throughout the region.
Also included are the 70 digital strong-motion sites being installed by USGS
National Strong Motion Program (NSMP). The 470 strong-motion sites with be
connected with dial-up telephone telemetry, in addition some of the sites
will also provide realtime information via continuous telemetry. Current
station information can be found on the TriNet homepage, (http://www.trinet.org).
Collaborations
The TriNet Project emphasizes cooperation between federal and state
government agencies, university research, and the private sector. It is
being built on the infrastructure provided by these groups in Southern
California. The CUBE (Caltech-USGS Broadcast of Earthquakes) project
started in 1991 has formed a consortium of government agencies and private
industry concerned with earthquake hazards in southern California (Kanamori
et al., 1991). This group has built support for the project and provided
valuable user input into the design of the earthquake information systems.
Lessons for other seismic networks
The experience gained in southern California may provide practical
information for other regions that are planning extensive seismic monitoring
networks.
- The key to successful cooperation between diverse groups such as
earthquake engineers, research seismologists, and emergency planners, is an
understanding of the needs and motivations of each group. Conflicting data
requirements are often difficult (and sometimes impossible) to reconcile
between the various groups when building a multi-purpose system and a
successful network requires much coordinated discussion and planning.
- Timeliness should be a priority for getting instrumentation up and
running. Bringing parts of the network online over time is better than
trying to build the entire system in one step. Network operators have to
accommodate social pressures and expectations in the high-profile limelight
of earthquake recording.
- Data distribution and archiving are important parts of the seismic
system. Well-planned designs for fast data flow, large storage capacity,
and easy user accessibility are essential for obtaining the full benefit
from the seismic observations.
- Costs are always a major consideration in designing and implementing a
network. Purchasing hardware is only part of the cost and should constitute
only 50 to 70 percent of the total funds. The costs of installations,
software development, and system design are often underestimated in seismic
network deployments.
References
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