Continental Borderland Offshore Southern California
Written by Douglas Given, Lucy Jones, Egill HaukssonThe offshore area between the Patton Escarpment (continental slope) and the coast of southern California is known as the Continental Borderland. It is a series of generally northwest trending basins and ridges some of which extend above sea level as the Channel Islands. The ridges and basins are bounded by several major active faults (Figure 1). These are major tectonic features capable of producing damaging earthquakes in close proximity to several metropolitan areas of southern California. The are also potentially tsunamigenic. This structural fabric is part of the transform boundary between the Pacific and North American tectonic plates.
The SCSN is one of the largest and most automated seismic networks in the world. It consists of more than 350 analog and digital seismographic stations that relay both continuous and triggered seismic data back to a central computer facility in the Seismology Laboratory on the Caltech campus in Pasadena, Ca. Data from SCSN is used for a variety of research projects that would be enhanced if OBS data were gathered following offshore and near-shore events. Supplementing the SCSN with OBS sites following and offshore event would have several benefits; 1) more events would be recorded because the detection threshold would be lowered by denser station coverage, 2) location and depth determinations would be better constrained, and 3) magnitude determinations would improve.
There are several earthquake scenarios that could justify mobilization of the RMOBS system.
DATE TIME(GMT) LATITUDE LONGITUDE MAG LOCATION
1800 11 22 2130 33 0. 117 18.00 6.5 San Diego region
There are many harbors in southern California where vessels could be contracted to deploy the RMOBS instruments including Santa Barbara, Ventura-Oxnard, San Pedro-Long Beach, and San Diego.
Any data recorded by the RMOBS system must be integrated with the routine SCSN dataset to be of value. Parametric data (phase arrivals, amplitudes, etc), waveforms, and station metadata describing the instrument responses will be archived at the Southern California Earthquake Data Center (SCEDC) which will make it available to researched, engineers and the public.
ReferencesThe SCEC Borderland Working Group:Science and Data Collection Objectives, 2002
Evaluation of Tsunami Risk to Southern California Coastal Cities Mark R. Legg, Jose C. Borrero, and Costas E. Synolakis