Imaging a slow bilateral rupture with broadband seismic waves: The September 2, 1992 Nicaraguan tsunami earthquake

The spatio‐temporal rupture history of the September 2, 1992 Nicaragua tsunami earthquake (M_s=7.2; M_w=7.6) is analyzed using long‐period (157–288 s) Rayleigh and Love wave spectral inversions and an empirical Green function analysis of very broadband (10–250 s) body and surface waves. The event has a rupture duration exceeding 110 s with a slow (0.6–2.3 km/s) rupture velocity, and involves shallow dipping (6°–10°) thrust faulting at a shallow depth (≤ 10 km), with the latter being primarily responsible for the strong tsunami excitation. Two subevents dominate the source radiation, resulting from a slow asymmetric bilateral, 100–160 km long rupture. Long‐period surface wave directivity reveals a predominant rupture azimuth of 140° ± 30°, consistent with asymmetric extension of the bilateral rupture at an azimuth of 125° ± 30° resolved by the source time function analysis. An inverse Radon transform of the source time functions confirms the asymmetric bilateral rupture characteristics.