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High precision earthquake locations reveal seismogenic structure beneath Mammoth Mountain, California

January 1, 2003

In 1989, an unusual earthquake swarm occurred beneath Mammoth Mountain that was probably associated with magmatic intrusion. To improve our understanding of this swarm, we relocated Mammoth Mountain earthquakes using a double difference algorithm. Relocated hypocenters reveal that most earthquakes occurred on two structures, a near-vertical plane at 7–9 km depth that has been interpreted as an intruding dike, and a circular ring-like structure at ∼5.5 km depth, above the northern end of the inferred dike. Earthquakes on this newly discovered ring structure form a conical section that dips outward away from the aseismic interior. Fault-plane solutions indicate that in 1989 the seismicity ring was slipping as a ring-normal fault as the center of the mountain rose with respect to the surrounding crust. Seismicity migrated around the ring, away from the underlying dike at a rate of ∼0.4 km/month, suggesting that fluid movement triggered seismicity on the ring fault.

Citation Information

Publication Year 2003
Title High precision earthquake locations reveal seismogenic structure beneath Mammoth Mountain, California
DOI 10.1029/2003GL018334
Authors Stephanie G. Prejean, Anna Stork, William L. Ellsworth, David Hill, Bruce R. Julian
Publication Type Article
Publication Subtype Journal Article
Series Title Geophysical Research Letters
Series Number
Index ID 70025055
Record Source USGS Publications Warehouse
USGS Organization Alaska Science Center