Reliable Moment Magnitudes (Mw) of Smaller Size Events Using Coda Waves

Date: 4/25/2019

Time: 06:00 PM

Room: Fifth Avenue

The uneven distribution of stations and heterogeneous structure of the earth makes it difficult to calculate reliable moment magnitudes, especially for smaller events. Such magnitudes are important for event characterization, and its applications. The complex structure of the lithosphere in many regions causes significant variation in the recorded amplitude of direct body and surface waves that travel along different paths. These 2-D and 3-D effects are most significant for small-to-moderate sized events, which are mostly observable at periods < 10 seconds.

By contrast, the coda wave calibration method for source spectra and moment magnitude estimation has proven to be very robust in many regions with complex tectonic structure (i.e., Middle East, Caucasus, Central Asia). A direct moment magnitude calculation using the coda calibration technique has been successfully applied down to magnitude 3.0, thus eliminating the need for magnitude conversion (e.g., M_L to Mw) that can introduce large uncertainties. The reason why it is important to estimate reliable magnitudes is twofold: 1) Almost all contemporary ground motion prediction equations used in PSHA are in terms of Mw; 2) Mw provides a better quantification of the size of earthquakes, particularly large earthquakes, for which other magnitude scales tend to saturate. We are currently developing a robust, Java-based calibration and measurement tool to compute source parameters. This tool is openly available to the scientific community to test and validate the robustness of the calibration technique.

Presenting Author: Rengin Gok

Authors