SCSN Real-time System Documentation
1. Mission Statement
The Caltech/USGS element of TriNet (SCSN/TriNet), in cooperation with other agencies, will record and analyze earthquake ground motions in southern California, and distribute that information quickly, to improve our understanding of earthquakes and their effects, to contribute to improving building codes and structural design, and to facilitate emergency response.
2. Goals
To achieve this mission, SCSN/TriNet is pursuing the following goals.
2.1. Seismographic network Operate a hardened seismographic network to record earthquake ground motions in southern California. The network must be dense enough to document the true distribution of ground motions and robust enough to operate successfully in even the largest possible earthquakes.
2.1.1. Record all ground motions of interest, including the largest ground motions during major earthquakes and smaller motions to characterize the earthquake hazard from background seismicity at all frequencies of seismological and engineering interest.
2.1.2. Continuously record ground motions, continuing to function and provide information even through power and communications failures or other disruptions during damaging earthquake sequences.
2.2 Interagency Cooperation. Cooperate with other agencies working to mitigate the earthquake hazard in southern California in the recording, analysis and distribution of information, especially the Division of Mines and Geology, the Office of Emergency Services, the Federal Emergency Management Agency, the Southern California Earthquake Center and Council of the National Seismic System.
2.3 Database of earthquake information. Create an easily accessible database of earthquake information in southern California for seismological and engineering research. The catalog of earthquakes will be used to evaluate the rate of seismicity. The high fidelity records of ground shaking during earthquakes will elucidate the earthquake source, document what level of shaking earthquakes produce and what level buildings endured, providing the knowledge society needs to build a resilient infrastructure. The database of earthquake phases will provide insight into the structure of the earth.
2.3.1. Create a catalog of parameters for all earthquakes of magnitude 1.8 and greater onshore within the SCSN reporting area and 2.5 offshore.
2.3.2. Record high fidelity data on-scale with broad-band sensors with sufficient density to produce maps of site response characteristics.
2.3.3. Record on scale, high fidelity data on broad-band sensors and accelerometers with sufficient density to characterize ground motions for all large earthquakes.
2.3.4. Record continuous ground motions from all broad-band sensors.
2.3.5. All these data will be easily accessible to researchers and practitioners.
2.4. Rapid distribution of information Distribute information about an earthquake rapidly after occurrence to save lives and property, by facilitating decision making and mitigating actions such as search and rescue, fire prevention, and deployment of engineers and inspectors for building inspection.
2.4.1. Determine and broadcast accurate estimates of earthquake parameters, such as magnitude and location within 1 minute of the ending of an earthquake rupture.
2.4.2. Distribute preliminary estimates of the ground shaking (ShakeMap) within 3 minutes of onset for moderate and large events. These estimates will be updated as further information is available.
2.4.3. Provide data acquisition and processing capability to other agencies that record ground motion instruments installed in critical structures and transmit this information for emergency response.
2.5. Pilot early warning system. Develop a pilot early warning system that would allow us to know that an earthquake has begun before damaging shaking arrives at more distant sites and conduct social science research on the use of such data to be ready to implement when funds for future SCSN/TriNet enhancements, including sufficient stations, are obtained.
2.5.1. Determine that an earthquake is in progress and estimate resulting ground motions within 5-10 seconds of the arrival of the P wave at nearby stations.
2.5.2. Processing systems will be expandable to accommodate the number of stations necessary for implementation of early warning. They will also be resilient to the strong shaking and high data flow rates in a major earthquake sequence.
3. System Requirements
The diverse goals of SCSN/TriNet put several demands on the system. The requirements are as follows.
3.1 Seismic sensors and data loggers
3.1.1. "Broad-band" sites must provide flat instrument response from 50 Hz-30 seconds. Approximately one-fifth of the broad sensors will have improved low frequency response to 120 or 360 seconds. They will be sited, away from structures of 2 or more stories, and preferentially at sites with low ambient ground noise.
3.1.2. "Strong motion" reference sites must provide flat instrument response in acceleration and on scale recording up to 2 g. In some cases these sites will also have a broad band seismometer. They will be sited away from structures of 2 or more stories. At least 70 of the real-time strong motion sensors will be reference sites located in major facilities or near groups of significant structures. All strong motion sites will have local recording capability.
3.1.3. "High frequency sites," in some cases using a single vertical component seismometer, needed to ensure the lower magnitude threshold of M1.8 will be quiet sites that provide resolution down to ambient ground noise.
3.2 Network requirements
3.2.1. To provide site response characteristics from smaller earthquakes, broad band sites must be spaced no greater than every 30 km and every 20 km in urban areas.
3.2.2. To provide ground motion contouring after moderate and large earthquakes, telemetered strong motion sites (including the broad band sites that also have strong motion sensors) must be spaced at least every 20 km.
3.2.3. To provide a magnitude completeness threshold of 1.8 and a location accuracy of 1 km for most events, a broad band or high frequency sensor must be spaced every 25 km if at least 100 sites are quiet, or every 20 km if not. "Quiet" sites have significantly lower than average ground noise and in general are only achieved away from all structures and usually without AC power.
3.2.4. To achieve early warning, spacing of any station type along targeted faults must not exceed 10 km. The pilot early warning system for the San Andreas fault requires station spacing of 15 km or less.
3.3 Telemetry
3.3.1. To provide resiliency to strong shaking and other possible disruptions, we need a diversity of telemetry methods with multiple independent data paths. The system will be designed so that the loss of all signals through any single point of failure will not involve more than 30% of the stations and will not prevent attaining the mission's goals.
3.3.2. Methods that minimize the long term operational cost will be chosen as long as they do not compromise integrity (see 3.3.1).
3.3.3. To provide rapid locations and early warning, the data loggers must transmit their data to the central site within 2 seconds.
3.3.4. For reliability, the telemetry from all stations will be digital and hardened using technologies that provide immediate fail-over to backup components.
3.4 Data acquisition
3.4.1. The system will provide two-way communications capability for all stations. The system will verify the validity of received data and identify and provide separate processing for unverified data.
3.4.2. The system will be capable of acquiring data from digital data loggers made by a variety of manufacturers, from the existing analog network, from portable seismic instruments, from external networks including the TriNet/CDMG Element and USGS/NSMP, and from external data sources.
3.4.3. The system design will allow for the development of backup recording and processing capability at a remote site to ensure operation of SCSN/TriNet in a major earthquake or any other event that causes catastrophic failure of the central recording site at Caltech. The Caltech site will operate with or without the existence of this backup site.
3.4.4. Earthquake monitoring software will be able to access waveform data across the computer network at the central site within 1 second after the data has been acquired and verified. The data acquisition will be able to operate for 7 days without loss of data when the data archive is inaccessible . If the data archive becomes inaccessible, all of the mission critical functions will continue uninterrupted using the same tools and procedures as normal operations.
3.5 Real time earthquake processing
3.5.1. Real-time earthquake data processing will be distributable across multiple computers in a computer network at the central site.
3.5.2. Real-time earthquake processing will include phase picking, first motion identification, phase association, and determination of earthquake location, peak ground motions, magnitude, and ground motion centroid. Each time of phase arrival will be automatically determined within 2 seconds of receipt by the central site and will be within 0.02 seconds of their value when assigned by a trained seismic analyst for 99% of the phases. Magnitude will be determined within 1 minute of the ending of an earthquake rupture in southern California with the estimate within 0.1 unit of the final value for 99% of the events. All real-time programs will have off-line counterparts.
3.5.3 Parametric results and ground motion analyses will be distributed through status displays, email, paging, computer network distribution of results, and rapid delivery methods for distribution of early warning messages. Current ground motions will be graphically displayed.
3.5.4. The system will be able to decide whether to generate early warning messages and to evaluate, prioritize, and select information to be sent out as rapid notification from predetermined rules of precedence.
3.5.5. Large earthquake simulations and/or real data including waveform and derived data from a large network will be used to verify system functionality.
3.6 Data Archive and Database
3.6.1. The archive system will be the authoritative database of all data associated with all earthquakes in the catalog, as well as station information. The most recent 24 hours of data must always be available for verification and modification.
3.6.2. The archive facility will maintain a close to real-time station history database, including parameters such as station locations, instrument types, responses, and maintenance history. This database will be updated automatically, as well as manually and will be available to system operators and outside users.
3.6.3. The archive system will archive 80-100 sps waveform data for events declared by the central system, as well as continuous data with lower sampling rates from the digital broad band stations. These data will be made available to the real-time processing system, the data analysts, as well as users of the data center, shortly after (about a minute) an event occurs.
3.6.4. The archive facility will assemble data sets associated with southern California earthquakes and large distant earthquakes of scientific interest, and make them easily accessible to scientific researchers, the seismic processing system and the general public through a WWW (or other GUI) interface. The system will be able to add waveforms to the data sets long after (days or months) the events occur.
3.6.5. All waveform data will be provided in the same format.
3.7 Data analysis tools and catalog production
3.7.1. Waveforms may be automatically analyzed to re-determine phase arrivals (including time, first motion, and reading quality) and amplitudes and used to calculate event locations, magnitudes, and focal mechanisms. All automatic procedures will have manual counterparts. The system will be capable of incorporating waveforms and parameters from external sources (e.g., portables and other regional networks). All earthquakes of M1.8 and greater onshore and M2.5 offshore will be in the catalog of the SCSN/TriNet.
3.7.2. All processing steps will be automated and modular to allow changes and improvements. Human data analysis will be limited to events of particular interest or those that fail quality tests in automatic analysis. Failed events should be less then 5% of the total. Significant failed events will be corrected immediately by the duty seismologist, while others will be corrected within 72 hours. Results of the data analysis processing will be written to the data archive.
3.7.3. Processing procedures and quality criteria will be documented. Results from each processing step will be logged and checked for acceptance using established criteria. Problems will be automatically corrected or communicated to operators as soon as they are detected. Events will flow through the processing steps individually rather then in batches.
3.7.4. Parameters and solutions will be calculated in a manner to maintain continuity with the long-term catalog. Event location procedures will support well-established features such as station delays, multiple crustal models, and 3-D models. Station information such as site locations, delays, and calibrations will be derived from data in the central database. Regional events, teleseisms, sonics, and blasts will be identified. The location accuracy will be within 1 km on land and 5 km offshore. Moment tensors will be catalogued for all earthquakes above M3.5.
3.7.5. Tools will be provided for interactive, graphical analysis of waveforms, phase picks (including teleseismic phases), amplitudes, locations, magnitudes, and focal mechanisms. All resulting data and modifications will be in the data archive and be propagated to external data consumers as appropriate.
3.7.6. Interactive analysis capabilities described above will be available to trusted remote users (e.g., the duty seismologist).
3.7.7. There will be a smooth transition, between the present system and the new one, with no part of the SCSN/TriNet catalog left unprocessed.
3.8 System operational requirements
3.8.1. Simple mechanisms will be developed and used to monitor health and status of a) stations and data loggers, b) in-house computers and software, c) auxiliary equipment such as generators, and d) quality of the incoming data and to communicate between operations and maintenance personnel. A simple problem-reporting mechanism will clearly describe and date complaints and repairs.
3.8.2. The system design will be such that the loss of one computer will not impair achievement of mission goals. All systems will be physically secured against earthquake shaking and physically and electronically secure against unauthorized use.
3.8.3. Automatic alarms through computer and paging systems will alert operators of computer system failures, large-scale telemetry failure, and significant earthquakes.
3.8.4. At least 85% of stations and telemetry will be working at any time. Any drop below this level will be an emergency requiring immediate 24-hour response.
3.8.5. The system will have appropriate documentation including system design, system installation and maintenance, system operations documentation, operator's manual, earthquake response manual, and troubleshooting manual.
3.8.6. A duty seismologist will always be on call to respond to significant or felt earthquakes. The duty seismologist will always be able to make permanent modifications to the parametric data.
3.8.7. Digital seismograms will be in the archive within 10 minutes. Parametric information, including hypocenter, phase, magnitude, and focal mechanism, will be in the catalog within 1 minute after the end of rupture.
3.9 Interaction with data users
3.9.1. Partnerships will be developed with interested private and public entities through the CUBE (Caltech/USGS Broadcast of Earthquakes) program to distribute earthquake data products, ongoing communication and interaction with their engineers and managers and educational programs.
3.9.2. Some more extensive partnerships will be developed with interested private and public entities that will include installation of seismic stations at their facilities and sharing the costs of telemetry and instrumentation.
3.9.3. Communication with outside users will be fostered to identify new user needs and provide a forum for sharing of ideas and technology.
3.10 Real-time distribution of information
3.10.1. Information from SCSN/TriNet will be distributed through 3 systems, which are (1) the Internet, (2) a high reliability Extranet, for use by CUBE participants and emergency responders, and (3) the CDMG data distribution system.
3.10.2. Hypocentral coordinates, magnitude, and moment tensor will be distributed through these 3 systems within minutes of an earthquake's occurrence. Amplitude of ground shaking will be mapped within 3 minutes of the occurrence of all events of M3.5 and larger and updated as significant new information becomes available. Waveforms of larger earthquakes will be available from individual stations within minutes of recording.
3.10.3. Data from CDMG stations and from the USGS strong motion program will be integrated into the SCSN/TriNet data set as soon as such data is acquired. Strong motion recordings of engineering interest will be transferred automatically to the CDMG data management facility for further distribution to the earthquake engineering community.
3.10.4. SCSN/TriNet information will be distributed on an open WWW server, coordinated by the SCEC Data Center. Web serving computers and local nets will be independent so that their failure will not cause failure of other parts of SCSN/ TriNet. The server will have the capacity to handle 1,000,000 requests and transfer 1,000,000,000 bytes in 24 hours.
3.10.5. Members of the CUBE project will have high priority access to TriNet information in a CUBE data distribution system. CUBE computers and local nets will be independent so their failure will not cause failure of other parts of SCSN/TriNet. The CUBE Extranet will have the capacity to provide reliable access at all times to all CUBE users. The CUBE radio pager system will have sufficient capacity so that earthquake parameters will be received within 3 minutes of their generation and ground shaking information within 10 minutes of its generation.
3.10.6. A pilot project to develop early warning capability will be established with at least 2 participating CUBE partners on a private broadcast network. Delay between the onset of significant ground motion and broadcast will not exceed 10 seconds. The system will continue to broadcast estimates of the location and magnitude of the largest event observed on the TriNet system in any 1 second window, until ground motion subsides below a threshold level.
3.11 Research and technology development
3.11.1. On-line phase picking algorithms for broad-band digital networks will be developed. The algorithm will pick all seismic phases from 3-component records, and will discriminate teleseismic events from regional events.
3.11.2. Methods to continuously measure the amplitude of ground motions for rapid magnitude calculation, ShakeMap, and real-time ground-motion displays will be developed.
3.11.3. Methods to associate phases and extrapolate ground motions will be developed for use in ShakeMap. The associated data will be used to determine the centroid of the ground-motion distribution.
3.11.4. Methods to determine seismic moment tensors for all earthquakes above M3.5 in real-time will be developed.
3.11.5. Methods for estimating site amplification factors, including frequency-dependent site amplification factors will be developed.
3.11.6. Methods to implement a pilot ground-motion early warning system will be developed. The early warning philosophy is to detect ground motion at nearby stations within a few seconds after the occurrence of an earthquake, extrapolate in time and space, and broadcast the information, updating as necessary. A user interface will be developed to predict the arrival time and amplitude of shaking for any given location based on the real-time estimates of southern California seismicity.
3.11.7. Synthetic data sets for large earthquakes (e.g., Landers, Northridge) will be generated for system stress tests, and other tests for ShakeMap, pilot early warning, and display. |
