Active LARSE Set to Explode in October

SCEC is continuing its preparations for the second phase of a major earthquake study of southern California, referred to as the Los Angeles Region Seismic Experiment (LARSE II). The purpose of the study is to increase understanding of the potential for earthquakes in southern California by mapping hidden earthquake faults like the one that caused the 1994 Northridge earthquake and by gathering data to estimate how severely the ground will shake in different places in future earthquakes.

The best way to achieve the goals of this study is to conduct a seismic imaging survey across the region. This survey is akin to obtaining a sonogram in the medical industry. Instead of using a sound generator to create the waves that produce an image, seismic waves are generated by both earthquakes and small detonations in shallow boreholes to create an image of the interior of the Earth.

In part one of the survey (October 1998 through spring 1999), SCEC is recording naturally occurring earthquakes on approximately 100 seismographs deployed along a line from Malibu to the Mojave Desert, passing through the epicenter of the Northridge earthquake. During part two (October 1999), SCEC will record seismic waves generated by small detonations in approximately 100 shallow boreholes on 1,000 seismographs deployed along the same line, from Santa Monica to the Mojave.

Receiving permission from landowners to conduct the experiment is progressing yet is a tedious process (what would you say if someone asked to detonate an explosion beneath your property?). Drilling the boreholes will begin in June, starting in the Malibu area and heading north at a rate of one hole each day.

Each hole will be lined with a 50-foot metal pipe that will be capped and locked for security. The holes will be loaded with the explosive material in mid-October, just before detonation, which will occur over three or four nights in late October. The explosive is detonated at night so that the resulting waves are not masked by common synthetic vibrations such as traffic and construction work. Each hole will then be filled as needed and the site returned to its original condition.