For some time, the Caltech/USGS Broadcast of Earthquakes (CUBE) system has been transmitting information such as magnitude and epicenter parameters to civil defense agencies, local governments and utility companies within minutes of an event. The goal of the Automated Monitoring Of Earthquake Strong-motion (AMOES) system is to enhance the CUBE system by providing rapid determination of strong ground motion accelerations after an event.
California Seismic Network
The seismicity in California is monitored by two large networks. The Southern California network is operated by the California Institute of Technology (Caltech) and the United States Geological Survey (USGS) in Pasadena and the Northern California network is operated by the University of California at Berkeley (UCB) and the USGS office in Menlo Park.
The Southern California network currently has 257 stations (up from 30 stations in 1970). It has recorded approximately 10,000 events a year between 1981-1992. In 1992, it recorded 40,000 events from the Big Bear (Ms 6.5 on 7/28/94) and the Landers (Ms 7.4 on 7/28/94) earthquakes. With the Northridge earthquake (Ms 6.7 on 1/17/94), it recorded 10,000 events during the first quarter of 1994.
The CUBE System
In 1990, Caltech and the USGS office in Pasadena initiated the CUBE system. CUBE is an earthquake hazard information system for emergency response. The goal of this system is to minimize the loss of life and property after a damaging earthquake by:
• Directing emergency services to the area of greatest potential damage
• Influencing prompt, effective response by providing timely information to governments
• Identifying areas of potential secondary hazards such as dams, chemical plants, pipelines
• Allowing faster determination of damage to lifelines, i.e. roads, power lines, water mains, gas lines
The information required to achieve the goal of the CUBE system includes:
• Location and magnitude of earthquakes to participating agencies in near real-time.
• Estimates of distribution of ground shaking following a significant event
• A system to warn of imminent ground shaking in the seconds after an event has initiated, but before waves actually reach sites that may be damaged
To provide information such as locations and magnitudes to CUBE members, the CUBE system has been using the existing network which consists of 240 short-period stations (340 channels) and 17 broadband stations. The analog data is continuously transmitted to the Caltech Data Center by radio and dedicated phone lines. The broadband stations contain Streckeisen STS-1 and STS-2 broadband seismometers, Kinemetrics FBA-23 force balance accelerometers and Quanterra 24-bit digitizers. Six stations continuously transmit data to Caltech using five leased phone lines and one satellite line (VSAT). The data from the other eleven stations is collected by dialing up the sites using telephone lines.
The data is processed to compute the magnitudes and locations. This information is then transmitted via a paging system to CUBE members within minutes following the events. The recipients of this information include:
• Civil defense agencies
• Private companies
• Local governments
• Media stations
The current state of the CUBE project has already demonstrated the usefulness of real time information to emergency services. Although this information is valuable, it does not provide the extent of ground acceleration details over the affected area. In addition, the current network has the following limitations 1) clipping of the low dynamic range stations during stronger events, 2) introduction of noise induced by the analog telemetry, and 3) lack of warning capabilities.
The AMOES System
Kinemetrics and Caltech are jointly working on the AMOES system to acquire and distribute details of strong motion in real time to CUBE members. This joint development is partially funded by the State of California. Kinemetrics is responsible for providing the recorders and sensors for the remote stations and Caltech is responsible for providing the data acquisition system at the central station. The pilot phase of this project consists of four stations temporarily deployed to evaluate the efficiency of the system. This phase will be expanded to 14 stations in the near future.
Each AMOES remote station will include:
- One Kinemetrics recorder, the Altus K2
- One Kinemetrics FBA force balance accelerometer
- One GPS receiver
The key features of the Altus K2 recorder are:
- Advanced technologies
- Multitasking environment
- Modularity and expandability
- Ease of data access, installation and maintenance
The AMOES stations will transmit parameters of the acceleration time history and the time history to the Caltech Data Center. The parameters currently being considered for processing at the station are:
- Trigger time
- Peak ground acceleration (time and value)
- Peak ground velocity (time and value)
- P & S time arrivals
- Single station calculation of magnitude and epicenter
The stations will transmit these parameters and the time history as encoded packets of information to Caltech using 56 Kbps links to a frame relay "cloud" using internet packets (TCP/IP). The frame relay link is provided by a telephone company. This company has also offered to install the remote stations at their switching facilities using redundant digital switching networks. Final transmission to Caltech will concentrate the data from the frame relay cloud and send it via T1 or T3 links. Also being considered is the transfer of data to the Berkeley Data Center to provide some redundancy to the network. (Should a catastrophic earthquake render the system at one site inoperable, the system at the other site will be able to determine and broadcast earthquake parameters for the affected region and thereby assist with estimates of regional damage).
The Caltech Data Center will be responsible for collecting the data and determining the spatial distribution of peak accelerations. This information will be broadcast to CUBE members via the current paging system and will provide detailed information about the affected area.
After enough stations have been installed to give sufficiently dense coverage, the AMOES system will enhance the current CUBE system by giving rapid detail of strong ground motion information and will offer the potential to have real time warning capabilities.