The July 2019 MW6.4 Ridgecrest, California earthquake and its distinct foreshocks were well recorded by local and regional stations, providing a great opportunity to characterize its foreshocks and investigate the nucleation mechanisms of the mainshock. In this study, we utilized the match-and-locate (M&L) method to build a high-precision foreshock catalog for this MW6.4 earthquake. Compared with the sequential location methods (matched-filter + cross-correlation-based hypoDD), our new catalog contains more events with higher location accuracy. The MW6.4 mainshock was preceded by 40 foreshocks within ～2 h (on July 4, 2019 from 15:35:29 to 17:32:52, UTC). Their spatiotemporal distribution revealed a complex seismogenic structure consisting of multiple fault strands, which were connected as a throughgoing fault by later foreshocks and eventually accommodated the 2019 MW6.4 mainshock. To better understand the nucleation mechanism, we determined the rupture dimension of the largest ML4.0 foreshock by calculating its initial rupture and centroid points using the M&L method. By estimating Coulomb stress change we suggested that the majority of foreshocks following the ML4.0 event and MW6.4 mainshock occurred within regions of increasing Coulomb stress, indicating that they were triggered by stress transfer. The nucleation process before the ML4.0 event remains unclear due to the insufficient sampling rate of waveforms and small magnitude of events. Thus, our study demonstrates that the M&L method has superior detection and location ability, showing potential for studies that require high-precision location (e.g., earthquake nucleation).

Min Liu;Miao Zhang;Hongyi Li

Department of Earth and Environmental Sciences,Dalhousie University,Halifax,Nova Scotia B3H4R2,Canada;School of Geophysics and Information Technology,China University of Geosciences(Beijing),Beijing 100083,China;Shanghai Sheshan National Geophysical Observatory,Shanghai 201602,China

地震学报（英文版）

[1]Min Liu;Miao Zhang;Hongyi Li-.Using the match-and-locate method to characterize foreshocks of the July 2019 MW6.4 Ridgecrest, California earthquake)[J].地震学报（英文版）,2022(04):213-242

foreshocks,Ridgecrest,hypoDD,throughgoing

Using,locate,characterize,July,MW6,California,earthquake,its,distinct,were,well,recorded,by,local,regional,stations,providing,great,opportunity,investigate,nucleation,mechanisms,mainshock,In,this,study,utilized,build,precision,catalog,Compared,sequential,location,methods,matched,filter,cross,correlation,our,new,contains,more,events,higher,accuracy,was,preceded,within,from,UTC,Their,spatiotemporal,distribution,revealed,complex,seismogenic,structure,consisting,multiple,fault,strands,which,connected,later,eventually,accommodated,To,better,understand,determined,rupture,dimension,largest,ML4,calculating,initial,centroid,points,using,By,estimating,Coulomb,stress,change,suggested,that,majority,following,occurred,regions,increasing,indicating,they,triggered,transfer,process,before,remains,unclear,due,insufficient,sampling,waveforms,small,magnitude,Thus,demonstrates,has,superior,detection,ability,showing,potential,studies,require

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