Anna Stork William L. Ellsworth David Hill Bruce R. Julian Stephanie G. Prejean 2003 <p><span>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.</span></p> application/pdf 10.1029/2003GL018334 en Wiley High precision earthquake locations reveal seismogenic structure beneath Mammoth Mountain, California article