Abstract
In this work we propose and apply a straightforward methodology for the automatic characterization of the extended earthquake source, based on the progressive measurement of the P-wave displacement amplitude at the available stations deployed around the source. Specifically, we averaged the P-wave peak displacement measurements among all the available stations and corrected the observed amplitude for distance attenuation effect to build the logarithm of amplitude vs. time function, named LPDT curve. The curves have an exponential growth shape, with an initial increase and a final plateau level. By analyzing and modelling the LPDT curves, the information about earthquake rupture process and earthquake magnitude can be obtained. We applied this method to the Chinese strong motion data from 2007 to 2015 with Ms ranging between 4 and 8. We used a refined model to reproduce the shape of the curves and different source models based on magnitude to infer the source-related parameters for the study dataset. Our study shows that the plateau level of LPDT curves has a clear scaling with magnitude, with no saturation effect for large events. By assuming a rupture velocity of 0.9 Vs, we found a consistent self-similar, constant stress drop scaling law for earthquakes in China with stress drop mainly distributed at a lower level (0.2 MPa) and a higher level (3.7 MPa). The derived relation between the magnitude and rupture length may be feasible for real-time applications of Earthquake Early Warning systems.
Highlights
The characterization of the seismic source in terms of earthquake magnitude and source radius is a routinely operation in any standard seismological laboratory
The methodology is based on the use of the time evolution of the P wave (LPDT curve) as a proxy for the source time function to extract earthquake magnitude and rupture duration
We improved the magnitude estimation based on the plateau level of LPDT curve, by using two different scaling coefficients with fixed C, which have been properly calibrated
Summary
The characterization of the seismic source in terms of earthquake magnitude and source radius (or length of the rupture) is a routinely operation in any standard seismological laboratory. Colombelli and Zollo (2015) looked at the time evolution of the early P-wave information and used it as a proxy for the rupture process of earthquakes to extract the seismic moment and rupture extent of moderate-to-large Japanese earthquake records., Nazeri et al (2019) explored a similar approach using strong-motion data of the 2016–2017 Central Italy sequence and estimated moment magnitude, fault length and average stress drop for each single event. For the computation of the LPDT curve of each event, the peak amplitudes Pd of all records are measured at every P-wave time window and the distance-corrected amplitudes (logPcd) are obtained as logPcd logPd − ClogR. The shape of the LPDT curve, as obtained from the average of many stations distributed over azimuth and distance, can be interpreted as a proxy of the Moment Rate Function (MRF), from the initial time up to its maximum peak value. Arrival of the absolute main peak value (at about 25 s), and this leads to a sag of the LPDT curve around 4 s
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