LARSE II Passive Phase in Full Operation

The 100-km long, linear LARSE II passive array spans the Santa Monica Mountains, San Fernando Valley, Western Transverse Ranges, San Andreas fault, and western Mojave Desert. The goals of the experiment are to examine crustal and upper mantle seismic velocity structure, seismic hazard associated with anomalous site amplification, and tectonic evolution of the westernmost Transverse Ranges.

The data collection and station maintenance are being performed by two field assistants who see to it that the stations operate continuously without equipment problems or power failure, including remote, buried sites running on battery power only.

Each station consists of a short-period (L22 or L4C, all 3-component) or broadband (Guralp CMG-40T, CMG-3ESP, or CMG-3T) sensor; Reftek 24-bit data recorder (continuous recording at 25 sps, triggered at 50 sps); GPS receiver; and power supplies.

Activities already accomplished in the LARSE II passive phase:

o Selecting and permitting seismometer sites

o Organizing the collection and testing of SCEC PBIC and IRIS PASSCAL equipment

o Arranging the deployment by teams from several institutions (UCLA, Caltech, USGS Pasadena and Menlo Park, UCSB)

o Arranging for two field assistants to do station maintenance, preliminary data processing, and long-term data archiving at the IRIS data management center

The successfully operating 84-station LARSE II passive array will continue to be in place through April 1999. The team at UCLA will also be involved in the deployment and data collection efforts of the LARSE II active-source and high-resolution phases, scheduled to take place in late 1999 (see separate news brief in this issue).

The following activities will complete the LARSE II passive phase:

o Station pull-out by multi-institutional teams, similar to the deployment

o Conversion of data to mseed format, corrections for timing errors, and sensor calibrations in preparation for long-term archiving

o Creation of teleseismic and local event waveform files containing seismic phases for analysis