Earthquake detection in the Jiangsu region, China using graphics-processing-unit-based Match & Locate and rapid earthquake association and location

Earthquake detection and location are essential in earthquake studies,which generally consists of two main classes:waveform-based and pick-based methods.To evaluate the ability of two different methods,a graphicsprocessing-unit-based Match&Locate(GPU-M&L)method and a rapid earthquake association and location(REAL)method are applied to continuous seismic data recorded by 24 digital seismic stations from Jiangsu Seismic Network during 2013 for comparison.GPU-M&L is one of waveform-based methods by waveform cross-correlations while REAL is one of pick-based method to associate arrivals of different seismic phases and locate events through counting the number of P and S picks and travel time residuals.Twenty-six templates are selected from the Jiangsu Seismic Network local catalog by using the GPU-M&L.The number of newly detected and located events is about 2.8 times more than those listed in the local catalog.We both utilize a deep-neural-network-based arrival-time picking method called PhaseNet and a shortterm/long-term average(STA/LTA)trigger algorithm for seismic phase detection and picking by applying the REAL.We then refine seismic locations using a least-squares location method(VELEST)and a high-precision relative location method(hypoDD).By applying STA/LTA and PhaseNet,1006 and 1893 events are associated and located,respectively.The newly detected events are mainly clustered and show steeply dipping fault planes.By analyzing the performance of these methods based on long-term continuous seismic data,the detected catalogs by the GPU-M&L and REAL show that the magnitudes of completeness are 1.4 and 0.8,respectively,which are smaller than 2.6 given by the local catalog.Although REAL provides improvement compared with GPU-M&L,REAL is highly dependent on phase detection and picking which is strongly affected by signal-noise ratio(SNR).Stations at southeast of the study region with low SNR may lead to few detections in the same area.

Near-surface structure from ambient-noise tomography and horizontal-to-vertical spectral ratio beneath the Nankou-Sunhe fault

Active faults pose a great threat to urban security.As the largest NW-trend active fault in Beijing area,the Nankou-Sunhe fault plays an important role in earthquake disaster and city construction.In this study,we collect continuous ambient noise data recorded by 43 temporary short-period seismograph between September 21th to October 12th 2019 to investigate the near-surface structure beneath the Nankou-Sunhe fault by using ambient noise tomography(ANT)and horizontal-to-vertical spectral ratio(HVSR)method.From ambient noise processing,fundamental-mode Rayleigh wave signals are clearly observed in the frequency band of 0.4-2.5 Hz.Then direct surface-wave inversion algorithm is applied to calculate the 3D shear-wave velocity model.Our results show that there is a sharp velocity contrast across the Nankou-Sunhe fault,with low velocities down to about 2 km on the hanging wall and high velocity on the footwall of the fault.According to the geological investigation,the low velocities are related to thicker sediments and Jurassic volcanic rock below which are the cap rock of the hydrothermal system.From the HVSR analysis,the HVSR curves of the sites near the fault shows double-peak,one less than 1 Hz and the other centered 7 Hz.After converting frequency to depth by the empirical equation,the results show that the thickness of sediments is thinned from southwest to northeast,which generally agrees well to field survey.Our results provide high-resolution near-surface structure for future study on disaster risk reduction and urban planning.

Evaluation on Urban Tourism Competitiveness of Beibu Gulf Rim Based on the Entropy Approach

The tourism competitiveness of the cities around the Beibu Gulf was studied using the entropy method from the perspective of the 14 indexes of tourism current competitiveness,tourism support competitiveness and tourism potential competitiveness.The results show that the cities of Sanya,Nanning and Haikou have the stronger competitiveness;the cities of Zhanjiang,Beihai,Chongzuo and Maoming have moderate competitiveness;and the cities of Yulin,Qinzhou,Yangjiang and Fangchenggang have the weak competitiveness.According to the analysis of the index weight and comprehensive ranking,almost each aspect contributes to the city competitiveness.The index weights of the tourism current competitiveness,tourism support competitiveness and tourism potential competitiveness are 0.27222,0.3938 and 0.33398,respectively.Based on the niche theory,the article put forward the strategies:dislocation development,balanced development and regional tourism competition and cooperation development.

Micro-Earthquake Seismicity and Tectonic Significance of the 2012 Ms 4.9 Baoying Earthquake,Jiangsu,China

On July 20,2012,the Ms 4.9 Baoying Earthquake occurred near the junction of Baoying County and Gaoyou City in Jiangsu Province,eastern China.Due to no obvious surface rupture and limited observation of earthquake sequence,the seismogenic structure of the Ms 4.9 Baoying Earthquake is still unclear.In this study,80 earthquakes provided by China Earthquake Network Center(CENC)are first relocated;and then the relocated 75 events with high signal-to-noise ratios as templates are utilized to scan through continuous waveform data(July 11 to August 31,2012)using graphics processing unit-based match and locate(GPU-M&L)technique.Then the Deep Denoiser,a deeplearning-based noise reduction technique,is used to further confirm some newly detected events;and the double-difference relocation(Hypo DD)algorithm is used to relocate the earthquakes.We detect and relocate more than twice as many events as the CENC routine catalog,which includes 15 foreshocks and 230 aftershocks.The results show that the foreshocks are mainly distributed in the NW direction along the extended SE section of the blind Xiagonghe fault(XF),which is orthogonal to the strike of the seismogenic fault of the Ms 4.9 Baoying Earthquake(Yangchacang-Sangshutou fault,named YSF).Most of the aftershocks are generally distributed along the NNE-trending YSF and illuminate a steeply dipping plane.This study reveals detailed spatiotemporal evolution of the earthquake sequence and suggests that the buried XF extends southeastward and cuts through the NNE-trending seismogenic YSF.