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Seismic hazard of the western Makran subduction zone: Insight from mechanical modelling and inferred frictional properties
Earth and Planetary Science Letters ( IF 4.8 ) Pub Date : 2021-02-26 , DOI: 10.1016/j.epsl.2021.116789
Sepideh Pajang , Nadaya Cubas , Jean Letouzey , Laëtitia Le Pourhiet , Seyedmohsen Seyedali , Marc Fournier , Philippe Agard , Mohammad Mahdi Khatib , Mahmoudreza Heyhat , Mohammad Mokhtari

Western Makran is one of the few subduction zones left with a largely unconstrained seismogenic potential. According to the sparse GPS stations, the subduction is accumulating some strain to be released during future earthquakes. To enhance the seismic hazard assessment, we here propose to study the finite deformation of the western Makran accretionary wedge. Mechanical modelling is used to retrieve the spatial variations of the frictional properties of the megathrust, and discuss its seismogenic potential. To do so, we first build a structural map along the Iranian part of the Oman Sea and investigate three N-S seismic profiles. The profiles are characterized by a long imbricated thrust zone that takes place at the front of the wedge. A diapiric zone of shallow origin lies in between the imbricated zone and the shore. Along the eastern and western shores, active listric normal faults seem to root down to the megathrust. Eastern and western domains have developed similar deformation, with three zones of active faulting: the normal faults on shore, thrusts ahead of the mud diapirs, and the frontal thrusts. On the contrary, no normal faults are identified along the central domain, where a seamount is entering into subduction. Two mechanical analyses are performed to retrieve the frictional properties of the megathrust. We first apply the critical taper theory to constrain the pore fluid pressure of the wedge. We then apply the limit analysis on two selected profiles. Along the eastern profile, a transition from very low to extremely low friction is required to activate the large coastal normal fault (μdeepeff = 0.01-0.06, μmiddleeff = 0.003-0.012). To propagate the deformation to the front, an increase of friction along the imbricated zone is necessary (μfronteff = 0.017-0.031). The method could not be applied on the incomplete western profile. However, since the deformation is similar to the eastern profile, the same transitions of friction are expected. The Central domain is also characterized by very low effective friction; but, the absence of normal fault does not allow to evidence any frictional transition.

Since dynamic effective friction coefficients are significantly lower than frictions at slow slip rate, the region of extremely low friction between the normal fault and the imbricated zone might reveal the location of a seismic asperity. The difference in deformation along strike would thus reveal the existence of two different asperities, one along the eastern domain and a second along the western domain. Since no earthquake have occurred in the region for, at least, the last 1000 years, an event of large magnitude may strike the Iranian Makran, in particular the Eastern domain.



中文翻译:

西部Makran俯冲带的地震危险:从机械模型和推断的摩擦特性中获得的见解

西马克兰(Western Makran)是仅有的几处俯冲带,而俯冲带却没有很大的震源潜力。根据稀疏的GPS站,俯冲作用正在积累一些应变,这些应变将在未来的地震中释放。为了加强地震危险性评估,我们在此建议研究西部Makran增生楔的有限变形。使用机械建模来获取大推力的摩擦特性的空间变化,并讨论其产生地震的潜力。为此,我们首先沿着阿曼伊朗部分建造了一张结构图,并研究了三个NS地震剖面。型材的特点是在楔形件的前部形成了一个长的楔形推力区。浅水区的根尖区位于带状区和海岸之间。在东西海岸,活跃的李斯特正断层似乎扎根于大推力。东部和西部地区已形成相似的变形,具有三个活动断层带:海岸上的正常断层,在泥浆底盘前方的逆冲和前缘逆冲。相反,在沿海域俯冲的中央区域没有发现正常断层。进行了两次机械分析,以检索大推力的摩擦特性。我们首先应用临界锥度理论来约束楔的孔隙流体压力。然后,我们将极限分析应用于两个选定的配置文件。沿东部剖面,需要从极低的摩擦过渡到极低的摩擦,以激活大型沿海正断层(活跃的李斯特正断层似乎根源于大推力。东部和西部地区已形成相似的变形,具有三个活动断层带:海岸上的正常断层,在泥浆底盘前方的逆冲和前缘逆冲。相反,在沿海域俯冲的中央区域没有发现正常断层。进行了两次机械分析,以检索大推力的摩擦特性。我们首先应用临界锥度理论来约束楔的孔隙流体压力。然后,我们将极限分析应用于两个选定的配置文件。沿东部剖面,需要从极低的摩擦过渡到极低的摩擦,以激活大型沿海正断层(活跃的李斯特正断层似乎根源于大推力。东部和西部地区已形成相似的变形,具有三个活动断层带:海岸上的正常断层,在泥浆底盘前方的逆冲和前缘逆冲。相反,在海山进入俯冲的中央区域没有发现正常断层。进行了两次机械分析,以检索大推力的摩擦特性。我们首先应用临界锥度理论来约束楔的孔隙流体压力。然后,我们将极限分析应用于两个选定的配置文件。沿东部剖面,需要从极低的摩擦过渡到极低的摩擦,以激活大型沿海正断层(具有三个活动断层带:海岸上的正常断层,泥浆底盘前方的推力和前缘的推力。相反,在海山进入俯冲的中央区域没有发现正常断层。进行了两次机械分析,以检索大推力的摩擦特性。我们首先应用临界锥度理论来约束楔的孔隙流体压力。然后,我们将极限分析应用于两个选定的配置文件。沿东部剖面,需要从极低的摩擦过渡到极低的摩擦,以激活大型沿海正断层(具有三个活动断层带:海岸上的正常断层,泥浆底盘前方的推力和前缘的推力。相反,在沿海域俯冲的中央区域没有发现正常断层。进行了两次机械分析,以检索大推力的摩擦特性。我们首先应用临界锥度理论来约束楔的孔隙流体压力。然后,我们将极限分析应用于两个选定的配置文件。沿东部剖面,需要从极低的摩擦过渡到极低的摩擦,以激活大型沿海正断层(进行了两次机械分析,以检索大推力的摩擦特性。我们首先应用临界锥度理论来约束楔的孔隙流体压力。然后,我们将极限分析应用于两个选定的配置文件。沿东部剖面,需要从极低的摩擦过渡到极低的摩擦,以激活大型沿海正断层(进行了两次机械分析,以检索大推力的摩擦特性。我们首先应用临界锥度理论来约束楔的孔隙流体压力。然后,我们将极限分析应用于两个选定的配置文件。沿东部剖面,需要从极低的摩擦过渡到极低的摩擦,以激活大型沿海正断层(μdËËpËFF = 0.01-0.06, μ一世ddËËFF= 0.003-0.012)。为了将变形传播到前部,必须沿着镶嵌区域增加摩擦力(μF[RØñŤËFF= 0.017-0.031)。该方法不能应用于不完整的西方剖面。但是,由于变形与东部轮廓相似,因此预计会有相同的摩擦过渡。中央区域的特征还在于非常低的有效摩擦。但是,没有正常断层并不能证明存在任何摩擦过渡。

由于动态有效摩擦系数显着低于慢滑移率下的摩擦,因此正常断层和已成岩带之间的极低摩擦区域可能会揭示出地震粗糙的位置。因此,沿罢工变形的差异将揭示出存在两种不同的凹凸,一种是沿东部地区,另一种是沿西部地区。由于至少在过去的1000年中该地区没有发生地震,因此可能发生大规模的事件,袭击伊朗的Makran,尤其是东部地区。

更新日期:2021-02-26
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