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

这些研究集中在系统地检测和量化地震和岩石性质在大地震事件之前和之后的演变变化。我们使用多种技术来检验北安那托利亚断层在Mw7.1级<s:1> zce地震之前加速断层过程的证据，并提供了<s:1> zce地震和Mw7.4级伊兹米特地震之前的震后影响的详细结果。该研究使用了密集断裂带阵列记录的大量波形数据集，其中几个站点位于Ýzmit和d<s:1> zce事件的破裂带内，这些站点从Ýzmit主震后几天开始运行，直到d<s:1> zce事件发生后约3个月。该数据集包含在震源附近记录的许多事件，在一段时间间隔内，包括Ýzmit地震的余震、震源前震和余震以及震源本身。先前的研究基于标准技术在触发模式地震图中检测到的约26000个事件，提供了有关断裂带结构和地震速度前后变化的高分辨率信息。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。为了详细研究断裂带的演化过程，研究人员开展了以下工作：(1)利用最近开发的波形匹配滤波技术检测台网运行期间所有可能的附加地震。(2)利用更新后的包含许多以前未发现的小事件的目录，在震源中心周围以及数据覆盖的整个区域寻找预示震前活动加速的模式。(3)在完整的更新数据集中识别重复事件簇，并利用重复事件簇的波形研究<s:1> zce主震发生时间内不同地点地震速度和震源性质的时间演变。与以往的研究相比，新发现的额外小事件将显著提高结果的分辨率。该项目预计将提供迄今为止最详细的结果，关于大型大陆走滑地震震源附近和周围的断层过程和岩石性质的时间变化。该研究可为地震起爆过程、震后效应等地震与断层物理方面提供基础性的现场研究结果。

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.