1984 Morgan Hill earthquake

1984 Morgan Hill earthquake
Morgan Hill
Date April 24, 1984 (1984-04-24)
Origin time 21:15:21 UTC [1]
Magnitude 6.2 Mw [1]
Depth 10 km (6.2 mi) [1]
Epicenter 37°17′N 121°46′W / 37.28°N 121.76°W / 37.28; -121.76Coordinates: 37°17′N 121°46′W / 37.28°N 121.76°W / 37.28; -121.76 [1]
Type Strike-slip [2]
Areas affected South Bay
Northern California
United States
Total damage $7.5–8 million [3][4]
Max. intensity VIII (Severe) [4]
Peak acceleration 1.3g at Coyote Dam [5]
Landslides Yes [4]
Casualties 21–27 injured [3][4]

The 1984 Morgan Hill earthquake (also Halls Valley earthquake)[6] occurred on April 24 at 1:15 p.m. local time in the Santa Clara Valley of Northern California. The shock had a moment magnitude of 6.2 and a maximum Mercalli intensity of VIII (Severe). The epicenter was located near Mount Hamilton in the Diablo Range of the California Coast Ranges. Nearby communities (including Morgan Hill) sustained serious damage with financial losses of at least US$7.5 million.


The earthquake occurred along the Calaveras Fault, with the epicenter 16 kilometers (9.9 mi) northeast of San Jose, and at a depth of 8 km (5.0 mi). The shock was felt in Sacramento in California's central valley.[7]


The earthquake was reported to be felt over an area of 120,000 square kilometers (46,000 sq mi). Morgan Hill was the worst affected, with a number of mobile homes sliding off foundations, and moderate damage to several masonry buildings in the city. The communities of San Jose, San Martin and Coyote were some areas that experienced minor damage.[6] In Santa Clara County, over 550 buildings were reported to have received at least minor damage.[8]


The outline of aftershocks show that the rupture propagated southeast over a 25 km (16 mi) section of the fault, as far as San Martin, to the location of the 1979 Coyote Lake earthquake's mainshock. That event's aftershock zone also stretched to the southeast.[7]

See also


  1. 1 2 3 4 ISC (2015), ISC-GEM Global Instrumental Earthquake Catalogue (1900–2009), Version 2.0, International Seismological Centre
  2. Cockerham, R.S.; Eaton, J.P. (1987), "The Earthquake and its Aftershocks, April 24 through September 30, 1984", The Morgan Hill, California, Earthquake of April 24, 1984 (PDF), U.S. Geological survey Bulletin 1639, United States Geological Survey, p. 17
  3. 1 2 USGS (September 4, 2009), PAGER-CAT Earthquake Catalog, Version 2008_06.1, United States Geological Survey
  4. 1 2 3 4 Stover, C. W.; Coffman, J. L. (1993), Seismicity of the United States, 1568–1989 (Revised), U.S. Geological Survey Professional Paper 1527, United States Government Printing Office, pp. 97, 175
  5. Shakal, A.; Gay, Jr., T. E.; Sherburne, R. (August 1984), "Morgan Hill earthquake - Caused record shaking force" (PDF), California Geology, California Division of Mines and Geology: 163
  6. 1 2 "The Morgan Hill Earthquake of 1984". Earthquakes in Your Backyard - And Tsunamis. Archived from the original on 2009-06-01. Retrieved 2009-05-29.
  7. 1 2 Toppozada, Tousson R. "Morgan Hill Earthquake of April 1984". California Division of Mines and Geology. Archived from the original on 2009-06-01. Retrieved 2009-05-29.
  8. "Remembering the 1984 Morgan Hill Earthquake". West Coast Earthquakes. Archived from the original on 2009-06-01. Retrieved 2009-05-29.

External links

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