The 1989 Earthquake Swarm Beneath Mammoth Mountain, California: An Initial Look at the 4 May Through 30 September Activity

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Journal Article: The 1989 Earthquake Swarm Beneath Mammoth Mountain, California: An Initial Look at the 4 May Through 30 September Activity

Abstract
Mammoth Mountain is a 50,000- to 200,000-year-old cumulovolcano standing on the southwestern rim of Long Valley in eastern California. On 4 May 1989, two M = 1 earthquakes beneath the south flank of the mountain marked the onset of a swarm that has continued for more than 6 months. In addition to its longevity, noteworthy aspects of this persistent swarm include (1) an exponential-like increase in the rate of activity through the first month; (2) a vertically oriented, planar distribution of hypocenters at depths between 6 and 9 km with a north-northeast strike (roughly perpendicular to the average T-axis orientation for the swarm earthquakes); (3) recurring spasmodic bursts (rapid-fire sequences of similar-sized earthquakes with overlapping coda) and occasional earthquakes with enhanced low-frequency energy; (4) a uniform temporal distribution of the four largest (M ~ 3) events over the first 4 months of the swarm with a cumulative seismic moment for the entire sequence through 30 September corresponding to a single M ~ 4 earthquake; (5) a b-value of 1.2; and (6) submicrostrain perturbations on the nearby borehole dilatometer, the first of which led the onset of swarm activity by more than 2 weeks. These aspects of the swarm, together with its location along the southern extension of the youthful Mono-Inyo volcanic chain, which last erupted 500 to 600 years ago, point to a magmatic source for the modest but persistent influx of strain energy into the crust beneath Mammoth Mountain.

Authors 
D.P. Hill, W.L. Ellsworth, M.J.S. Johnston, John O. Langbein, D.H. Oppenheimer, A.M. Pitt, P.A. Reasenberg, Michael L. Sorey and S.R. McNutt








Published Journal 
Bulletin of the Seismological Society of America, 1990





DOI 
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Online 
Internet link for The 1989 Earthquake Swarm Beneath Mammoth Mountain, California: An Initial Look at the 4 May Through 30 September Activity

Citation

D.P. Hill,W.L. Ellsworth,M.J.S. Johnston,John O. Langbein,D.H. Oppenheimer,A.M. Pitt,P.A. Reasenberg,Michael L. Sorey,S.R. McNutt. 1990. The 1989 Earthquake Swarm Beneath Mammoth Mountain, California: An Initial Look at the 4 May Through 30 September Activity. Bulletin of the Seismological Society of America. 80(2):325-339.


Related Geothermal Exploration Activities
Activities (1)


Areas (1)
  1. Long Valley Caldera Geothermal Area
Regions (0)