Lg body-wave magnitude scaling for the continental margin around Korea and japan

摘要

Regional body-wave magnitude scalings are essential for quantification of small and moderate-size earthquakes that are observed only up to regional distances. Crustally-guided shear waves, Lg, develop stably at regional distances in continental crusts and are minimally influenced by the source radiation patterns. Lg body-wave magnitude scalings, m _b(Lg); are widely used for assessment of sizes of regional crustal events. The m _b(Lg) scaling has rarely been tested in continental margins where Lg waves are significantly attenuated due to abrupt lateral variation of crustal structures. We test the applicability of m _b(Lg) scaling to the eastern margin of the Eurasian plate around the Korean Peninsula and Japanese islands. Both third-peak and root-mean-square (rms) amplitudes of Lg vary significantly according to the crustal structures along raypaths, causing apparent underestimation of m _b(Lg): Implementation of raypath-dependent quality factors (Q) allows accurate estimation of m _b(Lg); retaining the transportability of m _b(Lg) in the continental margin around Korea and Japan. The calibration constants for an rms-amplitude-based m _b(Lg) scaling are not determined to vary by region in the continental margin due to complicated crustal structures. The calibration constants are determined to be distance-dependent. Both the third-peak-amplitude-based and rms-amplitude-based m _b(Lg) scalings yield accurate magnitude estimates when raypath-dependent quality factors are implemented.