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1985 Michoacan Earthquake, Mexico
1
- September 19, 1985 13:17:49 UTC
- 18.55°N, 102.368°W, 20.2 km below surface
- Large subduction zone earthquake
- Magnitude 8.0; 7.6 aftershocks (09-21-1985)
Michoacan coast previously identified as aseismic (Priestley and Masters, 1985 and references therein)
Human Factor
IRIS SeismiQuery
Damage and human lost experienced in multiple states, Mexico City
At least 9,500 people died
About 30,000 people injured
At least 100,000 people homeless
$3-4 billion (U.S.) in damages
3,540 building collapsed or seriously damaged
- Severe damage in Mexico City related to strong ground motion (~0.5 Hz).
- Both lake bed material and hill zones experiences much stronger ground motion than the hard coastal rock at epicenter.
USGS NEIC
Consisted of two sub-events 25 seconds apart (reporting as single event)
Average mechanism:
strike = 298°
dip = 15° +/- 1.5°
slip = 268°, 230 cm
Mo = 10.3e27 dynes-cm
Photos from National Earthquake Information Center. http://earthquake.usgs.gov/earthquakes/world/events/1985_09_19.php
References
Priestley, Keith F., Masters, T. Guy, 1986, Source Mechanism of the September 19, 1985 Michoacan Earthquake and Its Implications, Geophysical Research Letters, v. 13, n. 6, pp. 601-604.
Sing, S. K., Castro, R., 1988, Some Aspects of Source Characteristics of the 19 September 1985 Michoacan Earthquake and Ground Motion Amplification In and Near Mexico City from Strong Motion Data, Bulletin of the Seismological Society of America, v. 78, n. 2, pp. 451-477.
Houston, Heidi, Kanamori, Hiroo, 1986, Source Characteristics of the 1985 Michoacan Mexico Earthquake At Periods of 1 to 30 Seconds, Geophysical Research Letters, v. 13, n. 6, pp. 597-600.
National Earthquake Information Center, USGS, http://earthquake.usgs.gov/regional/neic/, September 9, 2013.
1985 Michoacan Earthquake, Mexico
Replotted focal mechanism, from Houston and Kanamori, 1986