Inferring heterogeneity of fault properties and stress state of a megathrust fault from dynamic stress drop variations: A feasibility study in the northern Chilean subduction zone

我提出了一个研究项目，系统地调查在智利俯冲带的地震高度活跃的北方地震应力降的时空模式。为此，我计划一个综合的分析方法的基础上相结合的三个独立的应力降估计技术。最近的研究表明，应力降与断层强度和/或应力作用于断层。这表明，应力降可能是一个有价值的参数，以执行故障分割，以限制滑动和锁定行为或识别潜在的破裂障碍。然而，应力降的估计往往受到很大的不确定性，研究之间的可比性是困难的，分析的数据集往往是有限的。同时，应力降在空间和时间上的分布图像对于理解大逆冲断层地震的成核和破裂过程也有很大帮助，应力降测量通常来自于记录的位移谱的拐角频率。由于测量误差和对地震动力学的假设，它们涉及很大的不确定性。为了提高精度，我计划开发一种改进的方法，它结合了三种不同的技术：光谱比法，光谱叠加法和下限法。前两种方法是谱方法，第三种方法是基于震级频率分布和地震位置的方法。通过利用这些技术的协同作用，我假设它将有可能显着提高的鲁棒性和精度的measurement.A特别有趣的研究区域是智利的北方俯冲带，这被认为是一个地震空区主办的一个严重的巨型逆冲事件的潜力。2014年，该地区经历了MW8.1伊基克大推力地震，仅释放了部分储存的破裂潜力。自2006年以来，IPOC网络一直在调查该地区。已经开展了重要的基础工作，如编制包含100 000多次地震（包括前震和余震序列）的高分辨率地震活动目录，以及探测长期重复的地震序列。此外，详细的GPS为基础的研究存在独立约束同震滑移和后滑移分布。因此，该数据集提供了很大的可能性，分析数以千计的事件在一个自洽的方式，并比较推导出的应力降模式与大地测量的结果非常详细。这里提出的研究的主要贡献将是一个先进的方法应力降估计。我期望它在智利北方的应用将提供一个俯冲带应力降分布的前所未有的详细图像。此外，它将有助于改善我们仍然不足的认识之间的关系的应力降，摩擦性能，和所施加的应力。

I propose a research project to systematically investigate the spatiotemporal patterns of seismic stress drop at the seismically highly active northern Chilean subduction zone. For this I plan an integrative analysis approach based on the combination of three independent stress drop estimation techniques.Recent studies indicate that stress drop relates to the fault strength and/or the stress acting on the fault. This suggests that the stress drop may be a valuable parameter to perform fault segmentation to constrain the slipping and locking behavior or to identify potential rupture barriers. However, stress drop estimates often suffer from large uncertainties, comparability between studies is difficult, and the analyzed data sets often are limited. Simultaneously, a well- resolved image of the stress drop distribution in space and time could help greatly to understand the nucleation and rupture processes of megathrust earthquakes.Stress drop measurements are usually derived from corner frequencies of recorded displacement spectra. They involve large uncertainties due to measurement errors and assumptions about earthquake dynamics. To improve the accuracy, I plan to develop a refined methodology which combines three different techniques: a spectral ratio method, a spectral stacking method, and the lower bound approach. The first two approaches are spectra techniques, the third approach is based on the magnitude frequency distribution and earthquake locations. By exploiting the synergies of these techniques, I hypothesize that it will be possible to significantly enhance the robustness and accuracy of the measurements.A particularly interesting study region is the northern Chilean subduction zone which is considered as a seismic gap hosting the potential of a severe megathrust event. In 2014 the region experienced the MW8.1 Iquique megathrust earthquake which only released part of the stored rupture potential. The area has been surveyed by the IPOC network since 2006. Important underlying works such as the compilation of a high resolution seismicity catalog with over 100,000 earthquakes including for- and aftershock series and the detection of long-term repeating earthquake sequences have already been carried out. Additionally, detailed GPS-based studies exist which independently constrain the co-seismic slip and after-slip distribution. Therefore, this data set provides the great possibility analyze thousand of events in a self-consistent manner and to compare the derived stress drop patterns with geodetic results in great detail.The major contribution of the here proposed study will be an advanced method for stress drop estimation. I expect that its application to northern Chile will provide an unprecedentedly detailed image of the stress drop distribution in a subduction zone. Furthermore, it will help to improve our still insufficient knowledge of the relation between stress drop, frictional behavior, and applied stress.