Estimation of frictional properties and slip evolution on a long-term slow slip event fault with the ensemble Kalman filter: numerical experiments
Estimation of frictional properties and slip evolution on a long-term slow slip event fault with the ensemble Kalman filter: numerical experiments
复制标题
使用集合卡尔曼滤波器估计长期慢滑移事件断层的摩擦特性和滑移演化：数值实验
DOI：
10.1093/gji/ggz415
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发表时间：
2019
影响因子：
2.8
通讯作者：
Kazuro Hirahara and Kento Nishikiori
中科院分区：
文献类型：
--
作者：
Kanda Wataru;Utsugi Mitsuru;Takakura Shinichi;Inoue Hiroyuki;Kazuro Hirahara and Kento Nishikiori
在俯冲带观察到了各种各样的慢滑动事件。它们可以作为应力计，用于监测巨型逆冲断层在地震周期中的应力状态。在这项研究中，我们专注于长期的慢滑事件（LSSE）反复出现在下倾部分的巨型逆冲断层之间的慢地震。到目前为止，对大规模空间环境的数据分析和模拟研究都是独立进行的。在大气和海洋科学方面，已开发出数据同化方法，将联合收割机数据分析和模拟研究最佳地结合起来。我们开发了一种方法来估计摩擦性能和监测滑动演化的LSSE故障，与顺序的数据同化方法，集合卡尔曼滤波（EnKF）。为了验证该方法的有效性，我们对日本西南部的丰后海峡LSSE断层进行了数值孪生实验。首先，基于速率和状态相关的摩擦定律，我们在速率强化平板界面上设置了一个速率弱化的圆形LSSE贴片，其临界成核尺寸大于贴片的临界成核尺寸，并再现了观测到的Bungo Channel LSSE，其重现时间约为7年，滑移持续时间为1年。在此基础上，利用模拟的滑动模型，合成了含噪声的均匀分布台站的地表位移速率观测数据。使用我们的EnKF方法，我们成功地估计了摩擦参数和几个周期后的滑移率演变。其次，我们认为存在于LSSE断层的上倾部分的巨型逆冲断层的影响，所揭示的全球导航卫星系统（GNSS）数据的运动学反演研究，并在模型中添加了这个锁定区域的滑动赤字率。我们只从运动学上估计了锁定区域的滑动速率，但每个LSSE断层单元的准动力学运动方程包括了锁定区域产生的应力项。基于这个模型，我们合成了观测到的表面位移率数据的GNSS站的实际分布，并执行EnKF估计，包括锁定区域上的滑动率。锁定区域的滑移率可以快速反演。即使对于GNSS台站的实际分布，我们也可以成功地估计LSSE断层上的摩擦参数和滑动演化。因此，我们的双数值实验表明，我们的EnKF方法的有效性，虽然我们需要进一步的研究，实际的GNSS数据分析。
A variety of slow slip events at subduction zones have been observed. They can be stress meters for monitoring the stress state of megathrust faults during their earthquake cycles. In this study, we focus on long-term slow slip events (LSSEs) recurring at downdip portions of megathrust faults among such slow earthquakes. Data analyses and simulation studies of LSSEs have so far been executed independently. In atmosphere and ocean sciences, data assimilations that optimally combine data analyses and simulation studies have been developed. We develop a method for estimating frictional properties and monitoring slip evolution on an LSSE fault, with a sequential data assimilation method, the ensemble Kalman filter (EnKF). We executed numerical twin experiments for the Bungo Channel LSSE fault in southwest Japan to validate the method. First, based on a rate- and state-dependent friction law, we set a rate-weakening circular LSSE patch on the rate-strengthening flat plate interface, whose critical nucleation size is larger than that of the patch, and reproduced the observed Bungo Channel LSSEs with recurrence times of approximately 7 yr and slip durations of 1 yr. Then, we synthesized the observed data of surface displacement rates at uniformly distributed stations with noises from the simulated slip model. Using our EnKF method, we successfully estimated the frictional parameters and the slip rate evolution after a few cycles. Secondly, we considered the effect of the megathrust fault existing in the updip portion of the LSSE fault, as revealed by kinematic inversion studies of Global Navigation Satellite System (GNSS) data and added this locked region with a slip deficit rate in the model. We estimated the slip rate on the locked region only kinematically, but the quasi-dynamic equation of motion in each LSSE fault cell includes the stress term arising from the locked region. Based on this model, we synthesized the observed surface displacement rate data for the actual distribution of GNSS stations and executed EnKF estimations including the slip rate on the locked region. The slip rate on the locked region could be quickly retrieved. Even for the actual distribution of GNSS stations, we could successfully estimate frictional parameters and slip evolution on the LSSE fault. Thus, our twin numerical experiments showed the validity of our EnKF method, although we need further studies for actual GNSS data analyses.