(October 2000 to March 2003)
With the goal of establishing a Caribbean Tsunami Warning System for Puerto Rico, local (Dr. Victor Huerfano) and regional (Dr. Carlos Mendoza) seismic wave form analysis algorithms were adapted to the Caribbean region. At-risk regions need real-time determination of earthquake source information to assess the nature of the hazard in order to optimize emergency response. In 1998 FEMA and the University of Puerto Rico funded a project to upgrade the instrumentation of the Puerto Rico Seismic Network (PRSN) of the Department of Geology of the University of Puerto Rico at Mayaguez. As part of this project, 9 digital telemetered broad-band stations were installed on the main island of Puerto Rico and offshore islands. The digital waveforms are recorded and saved at the facilities of the PRSN. Also, since 1998 the PRSN operates the data center for the Middle-America Seismograph Consortium (MIDAS). A protocol has been established for participating seismic networks of the Caribbean, Central America, South America, and North America, to submit in near real time data on significant events in the Greater Caribbean region. Currently available methodologies for the routine computation of earthquake source parameters were modified and adopted for use in the Caribbean region based on regionally and locally-recorded seismic waveforms.
An analysis of digital broadband waveforms from the Puerto Rico Seismic Network (PRSN) – for local analysis – and the Incorporated Research Institutions for Seismology (IRIS) Digital Management Information Center – for regional analysis - is carried out to provide earthquake-faulting information in near-realtime. If possible, PRSN data will be supplemented with realtime broadband waveforms recorded by Global Seismograph Network (GSN) stations in the Caribbean and data submitted to the MIDAS Data Center.
For the regional analysis, the techniques developed by Ammon, Randall and Owens (Randall et al., 1995) were implemented to perform a regional moment-tensor inversion using all three components (vertical, transverse, and radial) available from the digital seismograph stations. An analogous methodology, now based on Zahradnik et al. (2001) was adapted for local analysis. In both methods, an inversion scheme is applied to identify the focal mechanism that best reproduces the seismic waveforms observed at regional and local distances (less than 12 degrees). For regional analysis theoretical waveforms are computed by applying a reflection-matrix technique that uses a prescribed crustal-velocity model. For loal analysis theoretical waveforms are computed by applying the Bouchon (1991) method that uses a prescribed crustal-velocity model. Prior to inversion, the observed records are deconvolved to remove the instrument response.
The application of these moment-tensor inversion methods in an semi-automatic manner should provide source parameters in near-realtime for earthquakes in Puerto Rico and the Caribbean.
We have also adapted to the Caribbean region the “Earlybird” methodology developed and used in the West Coast and Alaska Tsunami Warning Center. This package provides rapid earthquake location and magnitude and will provide the moment-tensor solution, but this is still under construction. As part of this the PRSN has acquired a display system, composed of 9 PC monitors under one CPU, allowing the acquisition and display of waveforms, earthquake location on a local and regional basis and iterative waveform analysis, all on separate displays.
These activities are in harmony with the long term plans of NOAA to establish a Caribbean Tsunami Warning Center at Mayaguez.
Bouchon, M., 1981. A simple method to calculate Green’s functions for elastic layered media. Bull. Seism. Soc. Am., 71:959-971.
Randall G., G. Ammon, and Owens, 1995. Geophysical Research Letters 22, 1665-1668
Zahradnk, J., Jansky, J., and Papatsimpa, K., 2001. Focal mechanisms of weak earthquakes from amplitude spectra and polarities. Pure and Appl. Geophys., 158, 647-665.
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