Nandan Shyam, Ram Sumit Kumar, Ouillon Guy, Sornette Didier
Swiss Seismological Service, ETH Zürich, Sonneggstrasse 5, 8092 Zürich, Switzerland.
Department of Management, Technology and Economics, ETH Zürich, Scheuchzerstrasse 7, 8092 Zürich, Switzerland.
Phys Rev Lett. 2021 Mar 26;126(12):128501. doi: 10.1103/PhysRevLett.126.128501.
Seismicity and faulting within the Earth's crust are characterized by many scaling laws that are usually interpreted as qualifying the existence of underlying physical mechanisms associated with some kind of criticality in the sense of phase transitions. Using an augmented epidemic-type aftershock sequence (ETAS) model that accounts for the spatial variability of the background rates μ(x,y), we present a direct quantitative test of criticality. We calibrate the model to the ANSS catalog of the entire globe, the region around California, and the Geonet catalog for the region around New Zealand using an extended expectation-maximization (EM) algorithm including the determination of μ(x,y). We demonstrate that the criticality reported in previous studies is spurious and can be attributed to a systematic upward bias in the calibration of the branching ratio of the ETAS model, when not accounting correctly for spatial variability. We validate the version of the ETAS model that possesses a space varying background rate μ(x,y) by performing pseudoprospective forecasting tests. The noncriticality of seismicity has major implications for the prediction of large events.
地壳内的地震活动和断层活动具有许多标度律，这些标度律通常被解释为表明存在与某种相变意义上的临界性相关的潜在物理机制。使用一个考虑了背景率μ(x,y)空间变异性的增强型流行病型余震序列（ETAS）模型，我们对临界性进行了直接的定量检验。我们使用包括确定μ(x,y)的扩展期望最大化（EM）算法，将该模型校准到全球的美国国家地震信息中心（ANSS）目录、加利福尼亚周围地区以及新西兰周围地区的Geonet目录。我们证明，先前研究中报道的临界性是虚假的，并且当没有正确考虑空间变异性时，可归因于ETAS模型分支比校准中的系统性向上偏差。我们通过进行伪前瞻性预测测试，验证了具有空间变化背景率μ(x,y)的ETAS模型版本。地震活动的非临界性对大事件的预测具有重大影响。
