Spatio-temporal changes of earthquake and fault zone properties before and after the Mw7.1 Duzce event

这些研究的重点是系统地努力检测和量化大地震事件前后地震和岩石性质的演变变化。我们使用多种技术来检查证据，加速断层前的Mw7.1 Düzce地震的北安纳托利亚断层，并提供详细的结果，Düzce和之前的Mw7.4伊兹米特地震的震后影响。该研究采用了由紧密的断层带阵列记录的大量波形数据集，其中几个台站位于Schizmit和Düzce事件的破裂带内，这些台站从Schizmit主震后几天开始运行，直到Düzce事件后约3个月。该数据集包含了在一段时间内靠近Düzce主震震源记录的许多事件，包括Düzce主震的余震，Düzce主震的前震和余震，以及Düzce事件本身。以前的研究的基础上检测到的触发模式地震图与标准技术的26000事件提供了高分辨率的信息，断裂带结构和地震速度的同/震后变化。发现隐藏在记录波形噪声中的额外小事件可以显著增加可用数据，并为跟踪地震和断层性质的时空变化提供前所未有的机会。为了详细研究断层带的演化过程，研究人员进行了以下工作：（1）使用最近开发的波形匹配滤波器技术来检测网络运行期间所有可能的额外地震。(2)使用更新的目录与许多以前未检测到的小事件来搜索模式，这些模式表明Düzce主震震源周围以及数据覆盖的整个地区的地震前活动加速。(3)在完整的更新数据集中识别重复事件群，并使用重复事件群的波形来研究迪兹采主震时间内不同位置的地震速度和震源特性的时间演化。与以前的研究相比，新检测到的额外小事件将显著提高结果的分辨率。预计该项目将提供迄今为止关于大型大陆走滑地震震源附近和周围断层过程和岩石性质随时间变化的最详细结果。这项研究可以提供地震引发过程、震后效应以及地震和断层物理学其他方面的基本现场结果。

The studies focus on systematic efforts to detect and quantify evolutionary changes of earthquake and rock properties that precede and follow large seismic events. We use multiple techniques to examine evidence for accelerated faulting process before the Mw7.1 Düzce earthquake on the North Anatolian fault, and to provide detailed results for postseismic effects following both the Düzce and the preceding Mw7.4 Izmit earthquakes. The study employs extensive waveform data set recorded by a tight fault zone array, with several stations located within the rupture zones of the Ýzmit and Düzce events, which operated from a few days after the Ýzmit mainshock until ~3 month after the Düzce event. The data set contains many events recorded in close proximity to the hypocenter of the Düzce mainshock, over a time interval including aftershocks of the Ýzmit earthquake, foreshocks and aftershocks of the Düzce mainshock, and the Düzce event itself. Previous studies based on ~26000 events detected in triggered-mode seismograms with standard techniques provided high-resolution information on the fault zone structure and co/postseismic changes of seismic velocities. Uncovering additional small events buried in the noise of the recorded waveforms can increase the available data significantly and offer unprecedented opportunities for tracking spatio-temporal changes of earthquake and fault properties. To examine in detail evolutionary fault zone processes, the investigators perform research focusing on the following tasks: (1) Use the recently developed waveform matched filter technique to detect all possible additional earthquakes during the operation period of the network. (2) Use the updated catalog with many previously-undetected small events to search for patterns indicative of accelerated pre-earthquake activity around the hypocenter of the Düzce mainshock, as well as in the entire region covered by the data. (3) Identify clusters of repeating events in the complete updated data set, and use waveforms of the repeating event clusters to study temporal evolution of seismic velocities and earthquake source properties at various locations across the time of the Düzce mainshock. The newly-detected additional small events will increase significantly the resolution of results compared to those of previous studies. The project is expected to provide the most detailed results to date on temporal changes of fault processes and rock properties near and around the hypocenter of a large continental strike-slip earthquake. The study can provide fundamental in-situ results on the earthquake initiation process, postseismic effects and other aspects of earthquake and fault physics.