Cross-Network Microseismic Relocations of Some Aftershocks From the 1992 Nicaraguan Tsunami Earthquake

Using earthquake phase information from discrete earthquake catalogs in Central America (Nicaragua and Costa Rica) we are determining precise earthquake locations for improving our understanding of the Middle America Trench (MAT) seismogenic interface near the southern terminus of the 1992 Nicaraguan "tsunami earthquake" (TsE). The Nicaraguan event, like other such TsEs, is unique in its slow rupture and increased tsunami potential, possibly due to reduced elastic strength in the shallow subduction environment [e.g., Masayuki and Kanamori, 1995]. The CRSEIZE network, which consisted of 20 on-land and 14 offshore broadband and short-period stations, ran from December 1999 through July 2001, and recorded ~10,000 events. The Nicaraguan network, consisting of numerous short-period on-land stations and running for over 20 years, is well equipped to record continental seismicity, however it is unable to adequately resolve hypocenters offshore and along the MAT interface. Overall, the Nicaraguan catalog has about 30,000 earthquakes, of which over 3,000 events overlap with the CRSEIZE deployment and can be used for direct cross-network relocations using a 3D V_P, V_P/V_S velocity model for the region [DeShon et al., 2005]. With these revised locations, we can perform relative relocations of nearby earlier Nicaraguan activity while holding the newer events fixed. The combination of phase data for precision event location from both networks are useful for determining the geometry of the shallow subduction environment, identifying possible unique characteristics of the TsE region, and inferring spatial variability in interface locking capable of rupturing in future large events.