Measuring and modeling postseismic deformation processes of Andaman Islands

苏门答腊-安达曼大地震（Mw 9.3）发生近十年后，对同震应力变化松弛的事后过程的理解仍然不完整。早期安达曼群岛GPS位移的建模表明，近场运动主要是由破裂的滑动下倾，但不同的研究人员归因于主要是多孔弹性，主要是粘弹性和主要是断层滑动过程的松弛元素，主要取决于他们的测量采样和建模工具。有趣的是，在安达曼数据中观察到的隆起和右侧水平剪切变形与径向对称粘弹性松弛模型的预测完全相反。然后，我们假设，无论是径向对称模型忽略了流动特性的不均匀性，这是很重要的理解地震周期，或瞬态滑移仍然占主导地位的近场信号年后的事件。GPS位移建模表明，2012年板内海洋地震的孪生（M8.6和M8.2）破裂可能加速了正在进行的缓慢滑动，沿着群岛下方逆冲断层的下部，滑动长达4-10厘米。因此，2004年12月苏门答腊-安达曼（Mw = 9.2）同震应力变化激发并受2012年M8.6和M8.2双地震干扰的持续震后变形是这项持续工作的主要目标。此外，还需要更好的模式，近场变形沿着安达曼群岛。目前，有模型，要么解释远场变形或近场变形，但不是两者都combined.Measurements将继续在安达曼群岛的五个连续和12个运动站。联合国难民事务高级专员办事处的设施已借出全球定位系统接收器，在这一地区运作。将使用GAMIT/GLOBK软件处理这些研究中心沿着以及周围IGS研究中心的数据。将使用PYLITH有限元软件对地震后变形进行建模，该变形结合了由于2004年同震变化和2012年苏门答腊双地震引起的后滑动和粘弹性松弛。收集的数据将在联合国志愿人员组织的设施存档，并向所有人开放。这项奋进是与印度班加罗尔的贾瓦哈拉尔·尼赫鲁高级科学研究中心合作进行的。在未来的一年里，我们将启动向印度大陆的该研究所和安达曼群岛当地人移交完整技术转让的程序，以维护GPS站网络。这包括培训当地人和班加罗尔的JNCASR人员。

Nearly a decade after the great (Mw 9.3) Sumatra-Andaman earthquake, the understanding of the post-event processes responsible for relaxation of the co-seismic stress change still remains incomplete. Modeling of early Andaman Islands GPS displacements indicated near-field motions were dominated by slip down-dip of the rupture, but various researchers ascribe elements of relaxation to dominantly poroelastic, dominantly viscoelastic and dominantly fault slip processes, depending primarily on their measurement sampling and the modeling tools used. Intriguingly, uplift and right-lateral horizontal shear deformation, observed in the Andaman data, is exactly opposite the predictions of radially-symmetric viscoelastic relaxation models. We hypothesized then that, either radially-symmetric models neglect heterogeneities in flow properties that are important to understanding the earthquake cycle, or transient slip still dominates the near-field signals years after the event. Modeling of GPS displacements suggests that the twin (M8.6 and M8.2) ruptures of 2012 intra-plate oceanic earthquakes could have possibly accelerated the ongoing slow slip, along the lower portion of the thrust fault beneath the Islands with a month long slip of 4-10 cm. Thus, the continuing postseismic deformation excited by the December 2004 Sumatra-Andaman (Mw = 9.2) co-seismic stress change and interfered by 2012 M8.6 and M8.2 twin earthquake, is the primary objective of this continued work. There is also the need for better models for the near field deformation along the Andaman Islands. Currently there are models that either explain the far field deformation or near field deformation but not both combined.Measurements will continue at five continuous and twelve campaign stations in the Andaman Islands. UNAVCO facility has loaned GPS receivers that are operating in this region. Data from these sites along with surrounding IGS sites will be processed using GAMIT/GLOBK software. PYLITH finite element software will be used to model the post seismic deformation combining both after slip and viscoelastic relaxation due to 2004 co-seismic change and that of 2012 Sumatra twin earthquakes. Data collected will be archived at the UNAVCO facility and is open for all. This endeavor is in collaboration with Jawaharlal Nehru Centre for Advanced Scientific Research Bangalore, India. In the coming year we will initiate the processes to hand over the complete technology transfer to this institute in main land India and to locals in the Andaman Islands to maintain the network of GPS stations. This includes training of the locals and those in JNCASR in Bangalore.