With few exceptions, intermediate‐depth seismicity is associated with active subduction. In the Alboran slab, which is located just east of the Gibraltar Strait in the westernmost Mediterranean, although evidence suggests subduction is no longer active, tens to hundreds of M < 5.0 earthquakes are observed every year at depths of ~80 km. In this paper, we relocated 58 such events recorded by the PICASSO temporary network using a 3‐D velocity model and implementing a grid‐search approach to minimize the normalized misfit between observed and predicted P and S wave arrival times. Meanwhile, we relocated 908 events recorded by the Spanish national network using the double‐difference method and gave a high‐precision picture of seismicity distribution within the slab. Relocation results reveal five clusters in this region separated by small gaps. Jointly considering relocation results and a 3‐D tomography model indicates one cluster is at a shallower depth above the northern, E‐W oriented arm of the Alboran slab, while the other four are aligned from north to south, parallel to the strike of the slab and near its core. Larger events are generally shallower and more scattered, while the deeper, more clustered events tend to have smaller magnitudes. Clusters further to the north show concentrated seismicity on narrow zones that dip ~45° to the south. We suggest this seismicity is associated with active necking and break‐off of the Alboran slab, which is progressing from north to south. Shear instability is likely to be the failure‐enabling mechanism for the occurrence of these earthquakes.
It is necessary to review changes in the interactions of indicators following the construction of the Three Gorges Dam (TGD) in order to explore the impact of the dam on ecology. Research on changes in interactions among indicators of the comprehensive social–economic–ecology system in the Yangtze River Basin is limited, and the objective of this study was to investigate how this system changed after the operation of the TGD, as well as how the indicators contributed to this change. Here, the correlational network approach using 38 data point indicators from 1949 to 2018 of the Yangtze River Basin was applied to analyze the changes in indicator interactions before and after the TGD operation. The TGD impoundment altered networks of the social–economic–ecological system in the Yangtze River Basin. Indicators are both less positively and less negatively connected. The number of synergy and trade-off networks clusters changed from two (Modularity = 0.33) to -six (Modularity = 0.23) and from two (Modularity = 0.015) to four (Modularity = 0.34) after the TGD operation, indicating that the sustainable development of the Yangtze River Basin might be at a middle level after the TGD operation. Further analysis revealed that the mean annual discharge, downstream fry runoff, and downstream counts of the eggs and larvae of four carp, diatom abundance index, breeding population of Chinese sturgeon, and annual precipitation contributed more to the changes in the networks after 2003.
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