High-resolution microseismicity study of possible magmatic intrusion in the Long Valley Caldera
During August 1982, a dense network of 14 seismic stations was deployed in the southwest moat of the Long Valley Caldera. Ten sites used three component seismometers, and all sites used digital event recorders sampling at 200 samples/s with an array trigger criterion to reject local noise and to ensure accurate relative timing. The network recorded microseismicity to magnitude zero, the USGS shots from Casa Diablo to Mono Lake and Adobe Hills, and small local shots to constrain the near surface velocity structure. Hypocenters, station corrections, and velocity structure were simultaneously determined using all this data. The analysis concentrated on a swarm of earthquakes which occurred during August 9, along a vertical plane which was tangent to the resurgent dome. The events occurred along a 0.5 km segment of the plane between depths of 2.5 to 3.5 km. Additional events occurred to depths of 9 km, but not directly beneath the swarm: the deeper events are located from 0.5 to 1.0 km from the swarm epicenters. The configuration suggests intrusion of magma or volatiles: the shallow swarm was above the intrusion; the deeper events occurred along the perimeter of the upwelling. Focal mechanisms of events within the swarm support this interpretation, and indicate that the tensional axis is perpendicular to the plane of seismicity. 18 references, 5 figures.
- Research Organization:
- Lawrence Livermore National Lab., CA (USA)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 6444065
- Report Number(s):
- UCRL-90278; CONF-840175-1; ON: DE85001076
- Resource Relation:
- Conference: Active tectonic and magmatic process in Long Valley Caldera, California conference, Napa, CA, USA, 24 Jan 1984; Other Information: Portions are illegible in microfiche products
- Country of Publication:
- United States
- Language:
- English
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