影像大地测量数据揭示2021希腊塞萨利地震序列潜在断层几何及其区域构造意义

Imaging geodesy data reveals potential fault geometry and regional tectonic implications of the 2021 Greece Thessaly earthquake sequence

利用一对升降轨InSAR干涉图进行地震二维形变的分解通常是推断孕震机制与断层几何较为常用的手段.但该手段实施于短时间内发生的地震序列案例则较为困难,因为很难确保每个事件的形变都能够恰好被一对干涉图所记录.短周期多轨道InSAR数据为二维同震形变的描述和断层几何的推演提供了丰富的数据支撑,也为分离地震序列中各地震的同震形变提供了可能.2021年希腊塞萨利地震序列为研究地震序列形变分解提供了一个宝贵实例.针对此案例,本文利用覆盖震区的17幅多时相多轨道InSAR数据联合解算了该地震序列中三次事件各自的二维形变,并对形变场分布进行了解译.经形变分析认定,地震序列中第二、三次事件属于盲断层发震.基于分解出的二维形变,本文进一步推断了第二、三次事件所对应的断层几何并分析了潜在的孕震机制.此次地震序列的发震断层为:两个SE-NW走向/东北倾的断层(事件一、事件二),一个NW-SE走向/西南倾的断层(事件三).经过对滑动模型、同震库仑应力以及前震/余震数据的分析,本文认为此次地震序列的潜在孕震机制可以解释为一次SSE-WNW走向的断层级联触发活动.此外,通过分析此次地震序列余震的空间分布发现了余震深度与断层面之间的线性关系,这为本文推断出的盲断层几何以及地震序列间的级联触发观点提供了佐证.

Two-dimensional(2D)co-seismic deformations,which are decomposed from a pair of ascending/descending InSAR interferograms,are now commonly used to infer the underlying mechanism of seismogenesis and fault geometry.However,it has difficulty implementing the decomposition in the case of earthquake sequences occurring in a short time,as it has obstacle to ensure that the co-seismic deformations of each event can be precisely recorded by a pair of ascending/descending interferograms.Nevertheless,the multi-track InSAR data acquired in a short revisit cycle can provide us abundant data for deriving 2D co-seismic deformations and further the unknown fault geometry.Also,it is a lamp for us to separate the co-seismic deformations related to each earthquake in this earthquake sequence.The 2021 Thessaly earthquake sequence provides a valuable example for studying the deformation decomposition of seismic sequences.In this case,17 multi-temporal and multi-track InSAR interferograms covering central Thessaly are used to jointly derive the 2D deformations of three events respectively.Moreover,the derived deformations are further interpreted.2D deformations indicate that both second and third event can be explained by a rupture process in a blind fault geometry.In this paper,their fault geometries are further deduced and their underlying seismogenesis mechanisms are described in detail.The seismogenic faults of this earthquake sequence are considered as follows:two SE-NW striking/NE dipping faults(eventⅠ/Ⅱ)and one NW-SE striking/SW dipping fault(eventⅢ).Based on analysis of the slip distribution and foreshock/aftershock data,it is concluded that the underlying seismogenic mechanism of this earthquake sequence can be explained by a cascade triggering towards SSE-WNW direction.Moreover,through analyzing the spatial distribution of the aftershocks,a linear relationship between the aftershock depth and fault plane can be found.It can provide an evidence for the inferred fault geometry and the cascade triggering mechanism in this earthquake sequence.