Earthquake Seismic Moment, Rupture Radius and Stress-drop from P-wave
Displacement Amplitude vs Time Curves
Abstract
The reliable determination of earthquake source parameters is a relevant
task of seismological investigations which ground nowadays on high
quality seismic waveforms collected by near-source dense arrays of
ground motion sensors. Here we propose a parametric modelling technique
which analyzes the time-domain P-wave signal recorded in the near-source
range of small-to-large size earthquakes. Assuming a triangular
moment-rate function and a uniform speed, circular rupture model, we
develop the equations to estimate the seismic moment, rupture radius and
stress-drop from the corner-time and plateau level of the average
logarithm of the P-wave displacement vs time curves (LPDT). The
constant-Q, anelastic attenuation effect is accounted by a
post-processing procedure that evaluates the Q-unperturbed moment-rate
triangular shape.
The methodology has been validated through the application to the
acceleration records of the 2016-2017 Central Italy and 2007-2019 Japan
earthquake sequences covering a wide moment magnitude range (Mw 2.5 -
6.5) and recording distance < 100 km. After correcting for the
anelastic attenuation function, the estimated average stress-drop and
the confidence interval (〈∆σ〉=0.60 (0.42-0.87) MPa and 〈∆σ〉=1.53
(1.01-2.31) for crustal and subcrustal events of Japan and
〈∆σ〉=0.36(0.30-0.44) MPa for Central Italy) show, for both regions, a
self-similar, constant stress-drop scaling of the rupture
duration/radius with seismic moment. The smaller sensitivity of the
spatially averaged, time-varying peak displacement amplitude to the
radiation from localized high slip patch on the fracture surface, could
explain the retrieved smaller average stress-drops for sub-crustal
earthquakes in Japan and M>5.5 events in Central Italy
relative to previous estimates using spectral methods.