Non-Poissonian earthquake occurrence in coupled stress release models and its effect on seismic hazard

Most seismic hazard estimations are based on the assumption of a Poisson process for earthquake occurrence, even though both observations and models indicate a departure of real seismic sequences from this simplistic assumption. Instrumental earthquake catalogues show earthquake clustering on regional scales while the elastic rebound theory predicts a periodic recurrence of characteristic earthquakes on longer timescales for individual events. Recent implementations of time-dependent hazard calculations in California and Japan are based on quasi-periodic recurrences of fault ruptures according to renewal models such as the Brownian Passage Time model. However, these renewal models neglect earthquake interactions and the dependence on the stressing history which might destroy any regularity of earthquake recurrences in reality. To explore this, we investigate the (coupled) stress release model, a stochastic version of the elastic rebound hypothesis. In particular, we are interested in the time-variability of the occurrence of large earthquakes and its sensitivity to the occurrence of Gutenberg–Richter type earthquake activity and fault interactions. Our results show that in general large earthquakes occur quasi-periodically in the model: the occurrence probability of large earthquakes is strongly decreased shortly after a strong event and becomes constant on longer timescales. Although possible stress-interaction between adjacent fault zones does not affect the recurrence time distributions in each zone significantly, it leads to a temporal clustering of events on larger regional scales. The non-random characteristics, especially the quasi-periodic behaviour of large earthquakes, are even more pronounced if stress changes due to small earthquakes are less important. The recurrence-time distribution for the largest events is characterized by a coefficient of variation from 0.6 to 0.84 depending on the relative importance of small earthquakes.     

Low detection capability of global earthquakes after the occurrence of large earthquakes: investigation of the Harvard CMT catalogue

We investigated the detection capability of global earthquakes immediately after the occurrence of a large earthquake. We stacked global earthquake sequences after occurrences of large earthquakes obtained from the Harvard centroid-moment tensor catalogue, and applied a statistical model that represents an observed magnitude–frequency distribution of earthquakes to the stacked sequence. The temporal variation in model parameters, which corresponds to the detection capability of earthquakes, was estimated using a Bayesian approach. We found that the detection capability of global earthquakes is lower than normal for several hours after the occurrence of large earthquakes; for instance, the duration of lowered detection capability of global earthquakes after the occurrence of an earthquake with a magnitude of seven or larger is estimated to be approximately 12 hr.     

黄河流域兰西城市群工业集聚与污染集聚的空间交互影响

城市群是黄河流域高质量发展的主要载体,理清城市群工业集聚与污染集聚的空间交互影响对城市群工业协同发展和污染联防联控具有现实意义。基于空间统计方法和空间联立方程模型,利用2010—2017年黄河流域兰西城市群41个县（区）数据分析工业集聚与污染集聚的空间交互影响。结果表明：工业集聚与污染集聚的空间格局均具有非均衡性和“路径依赖”。工业集聚与污染集聚之间存在“荣辱与共”的交互影响,工业集聚既促进污染集聚,污染集聚也促进工业集聚。工业集聚与污染集聚均具有空间依赖性,相邻县（区）之间的工业集聚与污染集聚存在空间交互影响。人口密度和经济水平既促进工业集聚,也促进污染集聚;环境规制既抑制工业集聚,也抑制污染集聚;政府干预、市场化率和投资水平促进工业集聚;技术水平抑制污染集聚,但产业结构却促进污染集聚。研究认为,工业协同发展是污染联防联控的根本,形成工业共建和污染共治的空间合力是黄河流域城市群高质量发展的必然选择。