At 20:08 on September 18,2024,Beijing time,an earthquake of magnitude 4.7 occurred in Feidong,Anhui Province(31.98°N,117.6°E).The China Earthquake Early Warning Network presented the first early warning resu...At 20:08 on September 18,2024,Beijing time,an earthquake of magnitude 4.7 occurred in Feidong,Anhui Province(31.98°N,117.6°E).The China Earthquake Early Warning Network presented the first early warning results 8.9 s after the earthquake.The China Earthquake Networks Center(CENC)released the automatic rapid report results 163 s after the earthquake and the official rapid report results 8 min after the earthquake.At the same time,the CENC reported a series of emergency products,including source parameters,seismic tectonics,historical earthquakes,focal mechanism,instrument seismic intensity and predicted intensity.The results showed that the earthquake was located at the junction of the southern section of the Tanlu Fault and the Feizhong Fault,with aftershocks distributed in the NEE direction.The focal mechanism solution indicates that the earthquake is essentially a strike-slip event.The predicted intensity in the vicinity of the epicenter reaches up to VI,involving 23towns that cover an area of about 1359 km^(2).Only one station near the epicenter shows a peak acceleration value greater than the fortification standard of the area,which may cause slight damage to some adjacent houses,consistent with the actual damage to buildings.展开更多
Determining the rupture directivity for small earthquakes is challenging due to the small source dimension and limited resolution of far-field observations.In recent years,the burst of near-source observations provide...Determining the rupture directivity for small earthquakes is challenging due to the small source dimension and limited resolution of far-field observations.In recent years,the burst of near-source observations provides great opportunities to study earthquake rupture.Here we present the rapid determination of the rupture directivity for the 2024 Feidong M4.7 earthquake using only one strong motion station located 4 km from the epicenter.We find that the polarization of S waves evolves during the rupture,indicating an azimuth change during the rupture propagation.Through comparing the data with the synthetic waveforms,we infer that the M4.7 event propagated dominantly to the southwest on the dextral Tanlu fault.Our inference is further validated through comparing the data with records at local stations for M3 earthquakes in the Feidong sequence.Our study highlights the superior application of near-source observations in earthquake source studies.展开更多
At 20:08,on September 18,2024,an M4.7 earthquake occurred along the Tanlu fault zone in the Feidong County of Hefei,Anhui Province.This earthquake is the largest event in the modern history of Hefei,which caused subst...At 20:08,on September 18,2024,an M4.7 earthquake occurred along the Tanlu fault zone in the Feidong County of Hefei,Anhui Province.This earthquake is the largest event in the modern history of Hefei,which caused substantial social impact.To reveal the seismogenic structure of the M4.7 Feidong earthquake sequence and assess seismic risks,we use data from both the permanent seismic network and a temporary dense nodal array deployed in the epicentral region prior to the mainshock for:(1)accurate location of the earthquake sequence and determination of the focal mechanisms;(2)obtaining the spatiotemporal distribution,b-value,and half-day occurrence frequency of the earthquake sequence.The Sentinel-1 satellite data are used to analyze the coseismic displacement.Additionally,velocity models from regional tomography and local high-resolution 2D active-and passive-source surveys across the Tanlu fault zone in the epicentral area are also used to reveal the detailed geometry of the seismogenic fault.The results indicate:(1)the M4.7 Feidong earthquake sequence is concentrated around 10.5 km in depth along a NW-dipping,subvertical fault which trends NE and is approximately 5 km in length;the focal mechanism solution also reveals that the fault hosting the mainshock is a subvertical strike-slip fault,driven by the regional compressional stress in ENE-WSW;the coseismic horizontal displacement on the surface caused by the M4.7 mainshock has a maximum value close to 1 mm;(2)the regional velocity model shows significant lateral variation in v_(S) in the source region,with the mainshock occurring in the area with higher velocity;high-resolution P-wave velocity structures obtained by full waveform inversion from active sources,and S-wave velocity structures from passive-source ambient noise tomography indicate that the mainshock occurred along the boundary between high-and low-velocity bodies,and the seismogenic fault dips NW;the deep seismic reflection profiling shows that the mainshock occurred within the Jurassic strata;(3)based on these results,we suggest the seismogenic fault for the M4.7 Feidong earthquake is either the Zhuding-Shimenshan fault,one of the major faults in the Tanlu fault zone,or a hidden fault to the east;the intersection of the NE-trending Tanlu fault zone and the WNW-trending Feizhong fault,along with significant velocity variations,likely create local stress concentrations which could have triggered the M4.7 Feidong earthquake sequence;(4)the strong aftershocks following the M4.7 Feidong mainshock did not further extend the fault rupture zone;the active period of the Zhuding-Shimenshan fault was the late Early Pleistocene to Middle Pleistocene,and the imaging results indicate that this fault does not cut through the shallow Feidong depression.In conjunction with the small coseismic rupture area,it is inferred that the probability of surface-rupturing earthquakes in the future is relatively low.展开更多
The Feidong district is located in the southern segment of the Tan-Lu fault zone that separates the South China Block(NCB)from the North China Craton(NCC).We report zircon U-Pb geochronology and Hf isotope data,as wel...The Feidong district is located in the southern segment of the Tan-Lu fault zone that separates the South China Block(NCB)from the North China Craton(NCC).We report zircon U-Pb geochronology and Hf isotope data,as well as whole-rock geochemistry for Xishanyi granodiorite and Jianshan granite in the Feidong district.Zircon U-Pb dating results show that the emplacement ages of the Xishanyi and Jianshan intrusions are 124±3 Ma and 130±1 Ma respectively,coeval with magmatic events linked to large-scale lithospheric thinning in eastern China.The whole-rock geochemistry of the Xishanyi and Jianshan intrusions demonstrate that they are peraluminous,high potassium calc-alkaline I-type granites with adakitic characteristics.Both intrusions underwent weak crustal assimilation during emplacement.The in situ zirconε(Hf)(t)values of the Xishanyi granodiorites range from-26.4 to-21.8,with T(DM2)model ages of 2552 to 2841 Ma.The in situ zirconε(Hf)(t)values of the Jianshan granite are from-27.5 to-23.0 with T(DM2)model ages of 2632 to 2904 Ma.The peak age of inherited zircon grains from the Xishanyi granodiorite and the Jianshan granite were^2.07 Ga and^1.94 Ga,respectively.After compared with the regional magmatism,we suggest that both the Xishanyi and Jianshan granitoid intrusions were derived from partial melting of the NCC lower crust.展开更多
基金supported by National Natural Science Foundation of China(52122811)。
文摘At 20:08 on September 18,2024,Beijing time,an earthquake of magnitude 4.7 occurred in Feidong,Anhui Province(31.98°N,117.6°E).The China Earthquake Early Warning Network presented the first early warning results 8.9 s after the earthquake.The China Earthquake Networks Center(CENC)released the automatic rapid report results 163 s after the earthquake and the official rapid report results 8 min after the earthquake.At the same time,the CENC reported a series of emergency products,including source parameters,seismic tectonics,historical earthquakes,focal mechanism,instrument seismic intensity and predicted intensity.The results showed that the earthquake was located at the junction of the southern section of the Tanlu Fault and the Feizhong Fault,with aftershocks distributed in the NEE direction.The focal mechanism solution indicates that the earthquake is essentially a strike-slip event.The predicted intensity in the vicinity of the epicenter reaches up to VI,involving 23towns that cover an area of about 1359 km^(2).Only one station near the epicenter shows a peak acceleration value greater than the fortification standard of the area,which may cause slight damage to some adjacent houses,consistent with the actual damage to buildings.
基金Suli Yao is partially supported by a Postdoc Fellowship from Faculty of Science,CUHK.Hongfeng Yang acknowledged the support from National Key R&D Program of China(No.2023YFF0803202)and HKSAR RGC(No.14308523)Zhigao Yang acknowledged the support from the Earthquake Spark Technology Project(No.XH23051B).
文摘Determining the rupture directivity for small earthquakes is challenging due to the small source dimension and limited resolution of far-field observations.In recent years,the burst of near-source observations provides great opportunities to study earthquake rupture.Here we present the rapid determination of the rupture directivity for the 2024 Feidong M4.7 earthquake using only one strong motion station located 4 km from the epicenter.We find that the polarization of S waves evolves during the rupture,indicating an azimuth change during the rupture propagation.Through comparing the data with the synthetic waveforms,we infer that the M4.7 event propagated dominantly to the southwest on the dextral Tanlu fault.Our inference is further validated through comparing the data with records at local stations for M3 earthquakes in the Feidong sequence.Our study highlights the superior application of near-source observations in earthquake source studies.
基金supported by the Anhui Province Science and Technology Breakthrough Plan Project(Key Project,No.202423l10050030)the National Natural Science Foundation of China(Fundamental Science Center Category B,No.4248830017)+4 种基金the Joint Funds of National Natural Science Foundation of China(No.U2139204)the National Natural Science Foundation of China Project(No.42104063)the Hefei Government Key Construction Project(No.2024BFFFD02048)the Earthquake Science and Technology Spark Program of the China Earthquake Administration(Nos.XH23020YA,XH24020B)the Anhui Mengcheng National Geophysical Observatory Joint Open Fund(No.MENGO-202307).
文摘At 20:08,on September 18,2024,an M4.7 earthquake occurred along the Tanlu fault zone in the Feidong County of Hefei,Anhui Province.This earthquake is the largest event in the modern history of Hefei,which caused substantial social impact.To reveal the seismogenic structure of the M4.7 Feidong earthquake sequence and assess seismic risks,we use data from both the permanent seismic network and a temporary dense nodal array deployed in the epicentral region prior to the mainshock for:(1)accurate location of the earthquake sequence and determination of the focal mechanisms;(2)obtaining the spatiotemporal distribution,b-value,and half-day occurrence frequency of the earthquake sequence.The Sentinel-1 satellite data are used to analyze the coseismic displacement.Additionally,velocity models from regional tomography and local high-resolution 2D active-and passive-source surveys across the Tanlu fault zone in the epicentral area are also used to reveal the detailed geometry of the seismogenic fault.The results indicate:(1)the M4.7 Feidong earthquake sequence is concentrated around 10.5 km in depth along a NW-dipping,subvertical fault which trends NE and is approximately 5 km in length;the focal mechanism solution also reveals that the fault hosting the mainshock is a subvertical strike-slip fault,driven by the regional compressional stress in ENE-WSW;the coseismic horizontal displacement on the surface caused by the M4.7 mainshock has a maximum value close to 1 mm;(2)the regional velocity model shows significant lateral variation in v_(S) in the source region,with the mainshock occurring in the area with higher velocity;high-resolution P-wave velocity structures obtained by full waveform inversion from active sources,and S-wave velocity structures from passive-source ambient noise tomography indicate that the mainshock occurred along the boundary between high-and low-velocity bodies,and the seismogenic fault dips NW;the deep seismic reflection profiling shows that the mainshock occurred within the Jurassic strata;(3)based on these results,we suggest the seismogenic fault for the M4.7 Feidong earthquake is either the Zhuding-Shimenshan fault,one of the major faults in the Tanlu fault zone,or a hidden fault to the east;the intersection of the NE-trending Tanlu fault zone and the WNW-trending Feizhong fault,along with significant velocity variations,likely create local stress concentrations which could have triggered the M4.7 Feidong earthquake sequence;(4)the strong aftershocks following the M4.7 Feidong mainshock did not further extend the fault rupture zone;the active period of the Zhuding-Shimenshan fault was the late Early Pleistocene to Middle Pleistocene,and the imaging results indicate that this fault does not cut through the shallow Feidong depression.In conjunction with the small coseismic rupture area,it is inferred that the probability of surface-rupturing earthquakes in the future is relatively low.
基金sponsored by the National Key Research and Development Program(2016YFC0600206)the Natural Science Foundation of China(41972076,91962218)the Structural Characteristics and Evolution of the Southern Segment of the Tan-Lu Fault Zone(DD20190043)。
文摘The Feidong district is located in the southern segment of the Tan-Lu fault zone that separates the South China Block(NCB)from the North China Craton(NCC).We report zircon U-Pb geochronology and Hf isotope data,as well as whole-rock geochemistry for Xishanyi granodiorite and Jianshan granite in the Feidong district.Zircon U-Pb dating results show that the emplacement ages of the Xishanyi and Jianshan intrusions are 124±3 Ma and 130±1 Ma respectively,coeval with magmatic events linked to large-scale lithospheric thinning in eastern China.The whole-rock geochemistry of the Xishanyi and Jianshan intrusions demonstrate that they are peraluminous,high potassium calc-alkaline I-type granites with adakitic characteristics.Both intrusions underwent weak crustal assimilation during emplacement.The in situ zirconε(Hf)(t)values of the Xishanyi granodiorites range from-26.4 to-21.8,with T(DM2)model ages of 2552 to 2841 Ma.The in situ zirconε(Hf)(t)values of the Jianshan granite are from-27.5 to-23.0 with T(DM2)model ages of 2632 to 2904 Ma.The peak age of inherited zircon grains from the Xishanyi granodiorite and the Jianshan granite were^2.07 Ga and^1.94 Ga,respectively.After compared with the regional magmatism,we suggest that both the Xishanyi and Jianshan granitoid intrusions were derived from partial melting of the NCC lower crust.
