Determination of Rupture Direction and Seismogenic Structure of the 2020 Heerlinger ML4.5 Earthquake in Hohhot,Inner Mongolia
Based on the observed waveform data of the regional digital seismic networks,the gCAP inversion method is used in three-dimensional space to obtain the centroid fine position of the HelingeerML4.5 earthquake on March 30,2020,which is 40.131° N,111.922°E,and the depth is 13 km.The strike/dip/slip of the first nodal plane are 279°/41°/-27° and those of the second nodal plane are 30°/72°/-127°.The moment magnitude is Mw3.98.The double-difference method named HypoDD algorithm is used to relocate the main shock and aftershock sequences,and the relocation results of 19 seismics events are obtained.The results show that the focal parameters of main shock are 111.858°E and 40.136°N,and the focal depth is 11.718 km.The aftershock sequences are bilaterally ex-tended along NW-SE direction and the subsurface rupture length is 4.6 km.The depth profile shows that the main shock is located in the middle of the aftershock area.The main rupture extends upward and downward simultaneously,and the depth distribution of the sequence ranges from 4 km to 17 km.The 20 sets of measurement results show that the NW-trending nodal plane Ⅰ is the seismogenic fault plane.Based on the research results of the geological structure of the focal area,the tectonic stress field and the three-dimen-sional crustal structure of the aftershock sequence distribution area,it is inferred that the seismogenic fault of the Helingeer ML4.5 earthquake is a NW-trending buried fault and the event is a left-lateral strike-slip mechanism with normal fault component.The earthquake occurred in the transition zone of high and low wave velocity conversion in the crust,which is located on the side of the high velocity body.Comprehensive analysis shows that influx of fluid materials plays an important role in triggering the earthquake event,and the complex fault structure not only provides pathways for fluid migration,but also controls the occurrence of earthquakes and the spatial distribution of seismic sequences.
The 2020 Helingeer ML4.5 earthquakeHypocenter-Centroid methodFocal mechanismSeismogenic structureNorthern margin of Ordos Block
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