Machine learning-based automatic construction of earthquake catalog for reservoir areas in multiple river basins of Guizhou province,China

Large reservoirs have the risk of reservoir induced seismicity.Accurately detecting and locating microseismic events are crucial when studying reservoir earthquakes.Automatic earthquake monitoring in reservoir areas is one of the effective measures for earthquake disaster prevention and mitigation.In this study,we first applied the automatic location workflow(named LOCFLOW)to process 14-day continuous waveform data from several reservoir areas in different river basins of Guizhou province.Compared with the manual seismic catalog,the recall rate of seismic event detection using the workflow was 83.9%.Of the detected earthquakes,88.9%had an onset time difference below 1 s,81.8%has a deviation in epicenter location within 5 km,and 77.8%had a focal depth difference of less than 5 km,indicating that the workflow has good generalization capacity in reservoir areas.We further applied the workflow to retrospectively process continuous waveform data recorded from 2020 to the first half of 2021 in reservoir areas in multiple river basins of western Guizhou province and identified five times the number of seismic events obtained through manual processing.Compared with manual processing of seismic catalog,the completeness magnitude had decreased from 1.3 to 0.8,and a b-value of 1.25 was calculated for seismicity in western Guizhou province,consistent with the b-values obtained for the reservoir area in previous studies.Our results show that seismicity levels were relatively low around large reservoirs that were impounded over 15 years ago,and there is no significant correlation between the seismicity in these areas and reservoir impoundment.Seismicity patterns were notably different around two large reservoirs that were only impounded about 12 years ago,which may be explained by differences in reservoir storage capacity,the geologic and tectonic settings,hydrogeological characteristics,and active fault the reservoir areas.Prominent seismicity persisted around two large reservoirs that have been impounded for less than 10 years.These events were clustered and had relatively shallow focal depths.The impoundment of the Jiayan Reservoir had not officially begun during this study period,but earthquake location results suggested a high seismicity level in this reservoir area.Therefore,any seismicity in this reservoir area after the official impoundment deserves special attention.

Generalization of PhaseNet in Shandong and its application to the Changqing M4.1 earthquake sequence

Waveforms of seismic events,extracted from January 2019 to December 2021 were used to construct a test dataset to investigate the generalizability of PhaseNet in the Shandong region.The results show that errors in the picking of seismic phases(P-and Swaves)had a broadly normal distribution,mainly concentrated in the ranges of−0.4–0.3 s and−0.4–0.8 s,respectively.These results were compared with those published in the original PhaseNet article and were found to be approximately 0.2–0.4 s larger.PhaseNet had a strong generalizability for P-and S-wave picking for epicentral distances of less than 120 km and 110 km,respectively.However,the phase recall rate decreased rapidly when these distances were exceeded.Furthermore,the generalizability of PhaseNet was essentially unaffected by magnitude.The M4.1 earthquake sequence in Changqing,Shandong province,China,that occurred on February 18,2020,was adopted as a case study.PhaseNet detected more than twice the number of earthquakes in the manually obtained catalog.This further verified that PhaseNet has strong generalizability in the Shandong region,and a high-precision earthquake catalog was constructed.According to these precise positioning results,two earthquake sequences occurred in the study area,and the southern cluster may have been triggered by the northern cluster.The focal mechanism solution,regional stress field,and the location results of the northern earthquake sequence indicated that the seismic force of the earthquake was consistent with the regional stress field.

Seismogenic environment and mechanism of the Yangbi M_(S)6.4 earthquake in Yunnan,China

The Yangbi M_(S)6.4 earthquake occurred on May 21,2021 in western Yunnan,China,where moderate earthquakes strike frequently.It exhibited a typical“foreshock-mainshock-aftershock”sequence and did not occur on a pre-existing active fault.The seismogenic environment and mechanism of this earthquake have aroused considerable research attention.In this study,we obtain the three-dimensional v_(P),v_(S)and v_(P)/v_(S)images using the v_(P)/v_(S)consistency-constrained double-difference tomography method,which improves the accuracy of v_(P)/v_(S)models.We focus on characteristics of v_(P)/v_(S)images in areas with a lateral resolution of 0.1°,and reveal the seismogenic environment of the Yangbi M_(S)6.4 earthquake.The conclusions are as follows:(1)Low velocity and high-v_(P)/v_(S)anomalies are revealed at different depths around the northern segment of the Red River fault.v_(S)and v_(P)/v_(S)images along the Weixi-Qiaohou-Weishan fault and the buried faults on its west show obviously segmented feature.(2)The source region of the Yangbi M_(S)6.4 earthquake is located in a low-v_(P)/v_(S)zone implying high medium strength.High-v_(P)/v_(S)anomalies in its NW direction indicate cracks development and the existence of fluids or partial melts,which are unfavorable for stress accumulation and triggering large earthquakes.Such conditions have also prevented the earthquake sequence from extending northwestward.(3)With the southeastward extrusion of materials from the Tibetan Plateau,fluid migration was blocked by the low-v_(P)/v_(S)body in the source region.The high-v_(P)/v_(S)anomaly beneath the source region may implies that the fluids or partial melts in the middle and lower crust gradually weakened medium strength at the bottom of the seismogenic layer,and preparing the largest foreshock in the transition zone of high to low v_(P)/v_(S).Meanwhile,tectonic stress incessantly accumulated in the brittle upper crust,eventually led to the M_(S)6.4 earthquake occurrence.

Interactive effects of elevation and land use on soil bacterial communities in the Tibetan Plateau

The Tibetan Plateau of China is uniquely vulnerable to the global climate change and anthropogenic disturbances.As soil bacteria exert a considerable influence on the ecosystem function,understanding their response to different climates and land-use types is important.Here,we characterized the bacterial community composition and diversity across three major ecosystems(cropland,forest,and grassland)in the Sygera Mountains of Tibet,along a typical elevational gradient(3300–4600 m).The abundance of taxa that preferentially inhabit neutral or weak alkaline soil environments(such as Actinobacteria,Thermoleophilia,and some non-acidophilus Acidobacteria)was significantly greater in the cropland than in the forest and grassland.Furthermore,the diversity of soil bacterial communities was also significantly greater in the cropland than in the forest and grassland.We observed a unimodal distribution of bacterial species diversity along the elevation gradient.The dominant phyla Acidobacteria and Proteobacteria exhibited consistent elevational distribution patterns that mirrored the abundance of their most abundant classes,while different patterns were observed for Acidobacteria and Proteobacteria at the class level.Soil pH was the primary edaphic property that regulated bacterial community composition across the different land-use types.Additionally,soil pH was the main factor distinguishing bacterial communities in managed soils(i.e.,cropland)from the communities in the natural environments(i.e.,forest and grassland).In conclusion,land use(particularly anthropogenic disturbances such as cropping)largely controlled soil environment,played a major role in driving bacterial community composition and distribution,and also surpassed climate in affecting bacterial community distribution.