Earthquake Variations Along the Middle America Trench, Central America

Subduction zones, home to the majority of the world's earthquakes, have also been the hosts for some of the world's most devastating tsunami. Seismic characteristics of subduction zone earthquakes, including the time constant of rupture, range from typical fast (few-10s seconds) ruptures to slow, long duration (100s of seconds) tsunami events, to silent (days-years) earthquakes that are observed geodetically rather than seismically. Causes for variations in the seismic parameters are currently not well understood, yet the causative factors influencing rupture could be very important in seismic and tsunami hazard assessment. Several aspects of subduction zone conditions may be important for influencing earthquake rupture, with our focus here on the effects of subducting plate inputs on earthquake rupture characteristics. Our main focus area for this study is along the Central American subduction zone because of the well-characterized input into the zone as well as detailed seismic catalogs. This region has also experienced slow, silent, and tsunami earthquakes in the past. We suggest that complexity on the subducting Cocos plate dictates variations in rupture characteristics for earthquakes over a range of magnitudes. Preliminary results for earthquakes larger than Mw=5.7 suggest earthquakes with slow rupture durations from southern Mexico through Costa Rica, with the slowest events occurring in the region between the high slip zones of the 1992 Nicaragua tsunami earthquake, away from imaged seamounts in the high slip regions. Slow earthquakes are also observed in southern Mexico. In addition, analysis of rupture characteristics of small magnitude (Mw<4) along the Costa Rica margin also suggests variations in stress drop that correspond with variations in geodetically estimated plate locking and rupture zones of past large earthquakes.