A change in seismicity near the Mid-America Trench following the Oaxaca earthquake

Immediately after the Oaxaca earthquake of November 29, 1978, the rate of occurrence of earthquakes (magnitude m_b ? 4.9) increased all along the Mid-America Trench, and stayed above the average level for the area for five months. The highest rate was recorded in the month just after the Oaxaca earthquake, after which the rate gradually declined for five months. No aftershocks of the Oaxaca earthquake are included in the counts. The past seismicity history of the area suggests that it is unlikely that the simultaneous timing is a simple matter of coincidences. These observations suggest that motion of the Cocos plate is episodic, and that stress changes are rapidly transmitted throughout the plate.