EMCA Central Asia seismic source model

Version History11 Sep 2019: Release of Version 1.1 with the following changes: (1) new licence: CC BY SA 4.0, modification of the title: removal of file name and version); (2) addition of ORIDs when available; (3) actualisation of affiliations for some authors The metadata of the first version 1.0 is available in the download folder.. Data and file names remain unchanged. Area Source model for Central AsiaThe area sources for Central Asia within the EMCA model are defined by mainly considering the pattern of crustal seismicity down to 50 km depth. Although tectonic and geological information, such as the position and strike distribution of known faults, have also been taken into account when available. Large area sources (see, for example source_id 1, 2, 5, 45 and 52, source ids are identified by parameter “source_id” in the related shapefile) are defined where the seismicity is scarce and there are no tectonic or geological features that would justify a further subdivision. Smaller area sources (e.g., source_id values 36 and 53) have been designed where the seismicity can be assigned to known fault zones.In order to obtain a robust estimation of the necessary parameters for PSHA derived by the statistical analysis of the seismicity, due to the scarcity of data in some of the areas covered by the model, super zones are introduced. These super zones are defined by combining area sources based on similarities in their tectonic regime, and taking into account local expert’s judgments. The super zones are used to estimate: (1) the completeness time of the earthquake catalogue, (2) the depth distribution of seismicity, (3) the tectonic regime through focal mechanisms analysis, (4) the maximum magnitude and (5) the b values via the GR relationship.The earthquake catalogue for focal mechanism is extracted from the Harvard Global Centroid Moment Tensor Catalog (Ekström and Nettles, 2013). For the focal mechanism classification, the Boore et al. (1997) convention is used. This means that an event is considered to be strike-slip if the absolute value of the rake angle is <=30 or >=150 degrees, normal if the rake angle is -150 and reverse (thrust) if the rake angle is >30 or <150 degrees. The distribution of source mechanisms and their weights are estimated for the super zones.For area sources, the maximum magnitude is usually taken from the historical seismicity, but due to some uncertainties in the magnitudes of the largest events, the opinions of the local experts are also included in assigning the maximum magnitude to each super zone. Super zones 2 and 3, which belongs to stable regions, are each assigned a maximum magnitude of 6, after Mooney et al. (2012), which concludes after analyses and observation of modern datasets that at least an event of magnitude 6 can occur anywhere in the world. For hazard calculations, each area source is assigned the maximum magnitude of their respective super zone.For processing the GR parameters (a and b values) for the area sources, the completeness analysis results estimated for the super zones are assigned to the respective smaller area sources. If the individual area source has at least 20 events, the GR parameters are then estimated for the area source. Otherwise, the b value is adopted from the respective super zone to which the smaller area source belongs, and the a value is estimated based on the Weichert (1980) method. This ensures the stability in the b value as well as the variation of activity rate for different sources.The hypocentral depth distribution is estimated from the seismicity inside each super zone. The depth distribution is considered for maximum up to three values. Based on the number of events, the weights are assigned to each distribution. These depth distributions, along with corresponding weights, are further assigned to the area sources within the same super zones.

版本历史
2019年9月11日：发布版本1.1，包含以下变更：(1) 新许可协议：CC BY SA 4.0，标题修改：移除文件名及版本号；(2) 新增可用的开放研究者与贡献者身份识别码（ORIDs）；(3) 更新部分作者的所属机构。第一版1.0的元数据可在下载文件夹中获取。数据及文件名保持不变。

中亚区域震源模型
EMCA模型中的中亚区域震源主要通过考虑深度达50公里的地壳地震活动模式来定义。此外，若可获得构造及地质信息（如已知断层的位置与走向分布），也会将其纳入考量。

在地震活动稀少且无构造或地质特征支持进一步细分的区域，定义了大型区域震源（例如，source_id为1、2、5、45及52的震源，相关形状文件（shapefile）中通过参数“source_id”标识震源ID）。在地震活动可归属于已知断层带的区域，则设计了小型区域震源（例如，source_id为36及53的震源）。

为通过地震活动统计分析获得概率地震危险性分析（PSHA）所需参数的可靠估计，鉴于模型覆盖的部分区域数据稀缺，引入了超级区域。这些超级区域通过结合具有相似构造体制的区域震源，并参考本地专家判断来定义。超级区域用于估计：(1) 地震目录的完整时间；(2) 地震活动的深度分布；(3) 通过震源机制分析得到的构造体制；(4) 最大震级；(5) 通过古登堡-里希特关系（GR relationship）得到的b值。

震源机制的地震目录取自哈佛全球质心矩张量目录（Ekström and Nettles, 2013）。震源机制分类采用Boore等人（1997）的约定：若rake角绝对值≤30°或≥150°，则视为走滑型地震；若rake角为-150°则为正断层型；若rake角>30°且<150°则为逆断层（冲断层）型。超级区域的震源机制分布及其权重均经过估计。

区域震源的最大震级通常取自历史地震活动，但由于最大事件震级存在不确定性，在为每个超级区域分配最大震级时也参考了本地专家的意见。属于稳定区域的超级区域2和3，根据Mooney等人（2012）的研究（其通过现代数据集分析与观测得出结论：全球任何地方至少可能发生6级地震），各自被分配最大震级6级。在危险性计算中，每个区域震源均采用其所属超级区域的最大震级。

在处理区域震源的古登堡-里希特参数（a值与b值）时，超级区域的完整性分析结果会被分配至相应的小型区域震源。若单个区域震源包含至少20个事件，则直接估计该区域震源的GR参数；否则，b值采用其所属超级区域的b值，a值则基于Weichert（1980）方法估计。这既保证了b值的稳定性，也体现了不同震源活动率的差异。

震源深度分布通过每个超级区域内的地震活动估计得出，最多考虑三个深度值。根据事件数量为每个分布分配权重，这些深度分布及其对应权重会进一步分配至同一超级区域内的各个区域震源。