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探测和量化地震和岩石性质在大地震事件前后的演变变化。我们使用多种技术来检验北安纳托利亚断裂上的Mw7.1 Düzce地震之前断层加速运动的证据，并提供关于Düzce地震和之前Mw7.4 Izmit地震的震后效应的详细结果。这项研究使用了由致密断层带阵列记录的大量波形数据集，几个台站位于亚兹米特和Düzce事件的破裂带内，从亚兹米特主震后几天到Düzce事件后约3个月。该数据集包含了在一段时间间隔内在杜兹主震震源附近记录的许多事件，包括多伦多兹米特地震的余震、杜兹主震的前震和余震以及杜兹事件本身。以前的研究基于标准技术在触发模式地震记录中检测到的约26000个事件，提供了关于断裂带结构和地震同震/震后速度变化的高分辨率信息。发现隐藏在记录波形噪声中的更多小事件可以显著增加可用数据，并为追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研究工作：(1)使用最近发展起来的波形匹配滤波技术来检测台网运行期间可能发生的所有额外地震。(2)使用包含许多以前未检测到的小震的更新目录来搜索Düzce主震震中周围以及数据覆盖的整个区域的加速震前活动模式。(3)在完整的更新数据集中识别重复事件簇，并使用重复事件簇的波形来研究杜兹斯主震发生时不同地点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。该项目预计将提供迄今为止关于大陆走滑大地震震中附近和周围断层过程和岩石性质的时间变化的最详细结果。这项研究可以为地震孕育过程、震后效应以及地震和断层物理学的其他方面提供基本的现场结果。

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.