Rapid Detection of Large Earthquakes Using Quasi-Finite-Source Green’s Functions in Moment Tensor Analysis

Rapid procedures (i.e. within 5 to 15 minutes) for earthquake and tsunami early warnings focus on earthquake location, depth, magnitude, and slowness, but initial tsunami early warnings are more often issued without knowing the mechanism of the earthquake. Kawakatsu (1998) proposed using a limited number of stations to automatically detect, locate and determine the source parameters of earthquakes occurring within a predefined region by computing moment tensors at each point of a grid from continuously streaming long-period waveform data. This method gives correct results in terms of detection and source characterization of up to M7 earthquakes offshore Japan (Tsuruoka et al., 2009). For major earthquakes (M8+), we propose to improve the point-source moment tensor inversion by using QFS Green’s functions (QFS GFs) that takes into account the finiteness of the rupture zone. Using a direct and single-step procedure, it becomes possible to monitor all Mw>3.5 earthquakes.