[论文解读] Evidence of Early Supershear Transition in the Mw 7.8 Kahramanmaraş Earthquake From Near-Field Records

Ares J. Rosakis, Mohamed Abdelmeguid+1 more|arXiv (Cornell University)|Feb 14, 2023

earthquake and tectonic studies被引用 8

一句话总结

该论文使用近场记录提供初期超剪切转变的野外证据，估计断层破裂速度约为1.55 Cs，转变长度约为19.45公里。

ABSTRACT

The Mw 7.8 Kahramanmaraş Earthquake was larger and more destructive than what had been expected for the tectonic setting in Southeastern Turkey. By using near-field records we provide evidence for early supershear transition on the splay fault that hosted the nucleation and early propagation of the first rupture that eventually transitioned into the East Anatolian fault. The two stations located furthest from the epicenter show a larger fault parallel particle velocity component relative to the fault normal particle velocity component; a unique signature of supershear ruptures that has been identified in theoretical and experimental models of intersonic rupture growth. The third station located closest to the epicenter, while mostly preserving the classical sub-Rayleigh characteristics, it also features a small supershear pulse clearly propagating ahead of the original sub-Rayleigh rupture. This record provides, for the first time ever, field observational evidence for the mechanism of intersonic transition. By using the two furthest stations we estimate the instantaneous supershear rupture propagation speed to be ~ 1.55 Cs and the sub-Rayleigh to supershear transition length to be around 19.45 km, very close to the location of the station nearest to the epicenter. This early supershear transition might have facilitated the continued propagation and triggering of slip on the nearby East Anatolian Fault leading to amplification of the hazard. The complex dynamics of the Kahramanmaraş earthquake warrants further studies.

研究动机与目标

• 促使理解土耳其东南部大型似板内地震的破裂动力学。
• 研究卡赫拉曼马拉斯地震在初始阶段和早期传播中是否表现出超剪切特征。
• 识别近场地面运动中的信号，指示相间断裂增长和超剪切转变。

提出的方法

• 分析来自多个观测站的近场地速度记录，以识别断层平行分量与法线分量。
• 在近场记录中表征超剪切断层破裂（断层平行占优）和近雷诺特征。
• 从两个最远观测站的近场观测中，以远场样近场方式估计瞬时超剪切断层传播速度。
• 从记录脉冲的相对时间/位置推断从近雷到超剪切的转变长度。

实验结果

研究问题

• RQ1 卡赫拉曼马拉斯地震的近场记录是否在早期传播阶段显示超剪切破裂的信号？
• RQ2 可用近场数据估计的瞬时超剪切断层破裂速度是多少？
• RQ3 从近雷到超剪切的转变长度估计值在哪里，它与观测站位置有何关系？

主要发现

• 距离震中最远的两个观测站显示出相对于法线分量更大的断层平行速度分量，指示超剪切特征。
• 离震中最近的观测站保留了大部分近雷特征，但也记录了在近雷断层之前的一个小的超剪切脉冲。
• 瞬时超剪切断层速度估计大约是剪切波速（Cs）的1.55倍。
• 从近雷到超剪切的转变长度估计约为19.45公里，接近最近观测站的位置。
• 观察到的早期超剪切转变可能有助于近旁东安纳托利断层的继续传播和触发。