Abstract

Large and great earthquakes occurring along the Acapulco-Ometepec segment of the Mexican subduction zone during this century are reexamined to better constrain locations of prior earthquake rupture zones and the history of earthquake recurrence. The 7 June 1982 Ometepec earthquakes are used as master events in a Joint Epicentral Determination relocation of the 1937 (MS 7.7), 1950 (MS 7.3), 1957 (MS 7.7), and 1962 (MS 7.2, 6.9) earthquakes and their principal aftershocks. Rupture zones for these older events are consistent with patterns of rupture seen for more recent events (i.e., epicenters near the coast and a narrow zone of aftershock activity between the trench axis and the coastline). Comparison of the 1937, 1950, and 1957 ruptures with that of the great (MS 8.0) 1907 earthquake, suggests that the later three events may represent a delayed, multiple rerupture of the 1907 zone. The time interval between the 1937 and 1950 shocks is short compared to similar-sized events in Oaxaca. Similar epicentral locations, overlapping aftershock zones, and a large difference in magnitude for the 1937 and 1950 events suggest that both events are part of the same recurrence episode and hence, do not constitute a recurrence interval. Based on this model, repeat times for large (MS ≧ 7.5) events range from 30+ yr for Ometepec to 50+ yr for Acapulco-San Marcos.

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