GNSS观测的2021年5月22日玛多M_(S)7.4地震同震位移及其约束反演的滑动破裂分布

Coseismic displacement and slip distribution of the 2021 May 22,M_(S)7.4 Madoi earthquake derived from GNSS observations

2021年5月22日青海省果洛州玛多县发生M_(W)7.4地震,此次地震产生的地表破裂在空间上表现出明显的分段特征.本文基于不同来源的GNSS连续观测网数据获取了此次地震的精细三维同震形变场,结果显示:观测到的最大水平位移量达到280 mm,最大垂直形变量仅为25 mm,暗示此次地震的逆冲分量较小;此次地震具有较为明显的左旋走滑特征,同震形变基本对称,在NW-SE向的影响范围更广,该方向上水平同震形变大于3 mm的震中距范围超过500 km.进而,本文以余震精定位结果和GNSS观测到的三维同震形变场为约束,构建了地表破裂线为折线、倾角为85°、倾向西南的断层模型,反演了滑动破裂分布.结果显示:滑动破裂分布在震中两侧不均匀,均破裂到地表,破裂深度达到15 km左右,最大滑移量为4.73 m,计算的矩震级为M_(W)7.37.该结果与余震精定位结果具有很好的一致性,破裂的极值区正好位于早期余震空区,推测该余震空区未来的发震风险性较低.最后基于反演结果模拟计算了震中区域形变和应变场,结合应变值在断层地表迹线东南侧呈现挤压特征和已有的研究成果,推测此次地震增强了巴颜喀拉块体在东部地区挤压应力的积累特征,导致东部地区发震危险性增强,值得后续跟踪研究.

On May 22,2021,an M_(S)7.4 earthquake struck in Madoi County,Guoluo Prefecture,Qinghai Province of China.The surface rupture caused by this earthquake shows obvious segmentation characteristics in space.Based on the observations of continuously operating GNSS networkes from different sources,we obtained the fine three-dimensional coseismic deformation field of the earthquake.The results show that the maximum horizontal displacement is 280 mm and the maximum vertical deformation is only 25 mm,indicating that the thrust component of this earthquake is small.The coseismic deformation,with obvious sinistral strike slip characteristics,is basically symmetrical with a wider influence range in NW-SE direction.The epicentral distance range with horizontal coseismic deformation greater than 3 mm in this direction exceeds to 500 km.Futher,constrained by the relocated results of the aftershocks and the 3 D coseismic deformation field observed by GNSS,we constructed a fault model with a broken surface fracture line,a dip angle of 85°and along the strike of SW.The result of coseismic slip distribution shows that the sliding fractures are unevenly distributed on both sides of the epicenter,and they all ruptured to the surface,with the depth of~15 km,the maximum sliding amount is 4.73 m,and the calculated moment magnitude M_(W)7.37.This result is consistent with the relocated results of aftershocks.The maximum rupture area is just located in the early aftershock gap,so we speculated that the future seismic risk in this gap is low.At last,we simulated the deformation and strain fields in the epicenter area based on the inversion results,and by combining the compression characteristics of the strain values on the southeast side of the fault surface trace and the existing research results,we concluded that this earthquake enhanced the accumulation characteristics of the compressive stress of the Bayan Har block in the eastern region.As a result,the seismic risk in the eastern region is enhanced,which is worthy of a follow-up study.