Rapid report of the December 18,2023 M_(S)6.2 Jishishan earthquake,Gansu,China

On December 18,2023,the Jishishan area in Gansu Province was jolted by a M_(S) 6.2 earthquake,which is the most powerful seismic event that occurred throughout the year in China.The earthquake occurred along the NWtrending Lajishan fault(LJSF),a large tectonic transformation zone.After this event,China Earthquake Networks Center(CENC)has timely published several reports about seismic sources for emergency responses.The earthquake early warning system issued the first alert 4.9 s after the earthquake occurrence,providing prompt notification that effectively mitigated panics,injuries,and deaths of residents.The near real-time focal mechanism solution indicates that this earthquake is associated with a thrust fault.The distribution of aftershocks,the rupture process,and the recorded amplitudes from seismic monitoring and GNSS stations,all suggest that the mainshock rupture predominately propagates to the northwest direction.The duration of the rupture process is~12 s,and the largest slip is located at approximately 6.3 km to the NNW from the epicenter,with a peak slip of 0.12 m at~8 km depth.Seismic station N0028 recorded the highest instrumental intensity,which is 9.4 on the Mercalli scale.The estimated intensity map shows a seismic intensity reaching up to IX near the rupture area,consistent with field survey results.The aftershocks(up to December 22,2023)are mostly distributed in the northwest direction within~20 km of the epicenter.This earthquake caused serious casualties and house collapses,which requires further investigations into the impact of this earthquake.

An open access dataset for strong-motion data(PGA,PGV,and Site V_(S30))of 2023 M6.2 Jishishan,Gansu,China earthquake

1.Introduction On December 18,2023,a M6.2 earthquake struck central China with epicenter at Jishishan,Gansu(35.70°N,102.79°E).In the USGS Latest Earthquake platform,the event was identified as M_(W)5.9,35.743°N,102.827°E,labeled 37 km WNW of Linxia Chengguanzhen,China.This study presents an open-access dataset comprising PGA and PGV records of the main-shock from 202accelerometers and 539 Micro-Electro-Mechanical System(MEMS)sensors within two arcdegrees of the epicenter.

An accessible strong-motion dataset(PGA,PGV,and site v_(S30))of 2022 M_(S)6.8 Luding,China Earthquake

A M_(S)6.8 earthquake occurred on 5th September 2022 in Luding county,Sichuan,China,at 12:52 Beijing Time(4:52 UTC).We complied a dataset of PGA,PGV,and site vS30 of 73 accelerometers and 791 Micro-Electro-Mechanical System(MEMS)sensors within 300 km of the epicenter.The inferred v_(S30)of 820 recording sites were validated.The study results show that:(1)The maximum horizontal PGA and PGV reaches 634.1 Gal and 71.1 cm/s respectively.(2)Over 80%of records are from soil sites.(3)The v_(S30)proxy model of Zhou J et al.(2022)is superior than that of Wald and Allen(2007)and performs well in the study area.The dataset was compiled in a flat file that consists the information of strong-motion instruments,the strong-motion records,and the v_(S30)of the recording sites.The dataset is available at https://www.seismisite.net.

Preliminary report of the September 5,2022 M_(S) 6.8 Luding earthquake,Sichuan,China

The 2022 M_(S)6.8 Luding earthquake is the strongest earthquake in Sichuan Province, Western China, since the 2017 M_(S)7.0 Jiuzhaigou earthquake. It occurred on the Moxi fault in the southeastern segment of the Xianshuihe fault, a tectonically active and mountainous region with severe secondary earthquake disasters. To better understand the seismogenic mechanism and provide scientific support for future hazard mitigation, we summarize the preliminary results of the Luding earthquake, including seismotectonic background, seismicity and mainshock source characteristics and aftershock properties, and direct and secondary damage associated with the mainshock.The peak ground displacements in the NS and EW directions observed by the nearest GNSS station SCCM are ~35 mm and ~55 mm, respectively, resulting in the maximum coseismic dislocation of 20 mm along the NWW direction, which is consistent with the sinistral slip on the Xianshuihe fault. Back-projection of teleseismic P waves suggest that the mainshock rupture propagated toward south-southeast. The seismic intensity of the mainshock estimated from the back-projection results indicates a Mercalli scale of Ⅷ or above near the ruptured area,consistent with the results from instrumental measurements and field surveys. Numerous aftershocks were reported, with the largest being M_(S)4.5. Aftershock locations(up to September 18, 2022) exhibit 3 clusters spanning an area of 100 km long and 30 km wide. The magnitude and rate of aftershocks decreased as expected, and the depths became shallower with time. The mainshock and two aftershocks show left-lateral strike-slip focal mechanisms. For the aftershock sequence, the b-value from the Gutenberg-Richter frequency-magnitude relationship, h-value, and p-value for Omori’s law for aftershock decay are 0.81, 1.4, and 1.21, respectively, indicating that this is a typical mainshock-aftershock sequence. The low b-value implies high background stress in the hypocenter region. Analysis from remote sensing satellite images and UAV data shows that the distribution of earthquake-triggered landslides was consistent with the aftershock area. Numerous small-size landslides with limited volumes were revealed, which damaged or buried the roads and severely hindered the rescue process.

Transient postseismic slip and aftershock triggering:A case study of the 2008 M_W7.9 Wenchuan Earthquake,China

In this study,we investigate how a stress variation generated by a fault that experiences transient postseismic slip(TPS)affects the rate of aftershocks.First,we show that the postseismic slip from Rubin-Ampuero model is a TPS that can occur on the main fault with a velocity-weakening frictional motion,that the resultant slip function is similar to the generalized Jeffreys-Lomnitz creep law,and that the TPS can be explained by a continuous creep process undergoing reloading.Second,we obtain an approximate solution based on the Helmstetter-Shaw seismicity model relating the rate of aftershocks to such TPS.For the Wenchuan sequence,we perform a numerical fitting of the cumulative number of aftershocks using the Modified Omori Law(MOL),the Dieterich model,and the specific TPS model.The fitting curves indicate that the data can be better explained by the TPS model with a B/A ratio of approximately 1.12,where A and B are the parameters in the rate-and state-dependent friction law respectively.Moreover,the p and c that appear in the MOL can be interpreted by the B/A and the critical slip distance,respectively.Because the B/A ratio in the current model is always larger than 1,the model could become a possible candidate to explain aftershock rate commonly decay as a power law with a p-value larger than 1.Finally,the influence of the background seismicity rate r on parameters is studied;the results show that except for the apparent aftershock duration,other parameters are insensitive to r.

Rapid report of source parameters of 2023 M6.2 Jishishan,Gansu earthquake sequence

The M6.2 earthquake in Jishishan,Gansu Province,on December 18,2023,caused extraordinary earthquake disasters.It was located in the northern part of the north−south seismic zone,which is a key area for earthquake monitoring in China.The newly built dense strong motion stations in this area provide unprecedented conditions for high-precision earthquake relocation,especially the earthquake focal depth.This paper uses the newly built strong motion and traditional broadband seismic networks to relocate the source locations of the M3.0 and above aftershocks and to invert their focal mechanisms.The horizontal error of earthquake location is estimated to be 0.5−1 km,and the vertical error is 1−2 km.The focal depth range of aftershocks is 9.6−14.6 km,distributed in a 12-km-long strip with SSE direction.Aftershocks in the south are more concentrated horizontally and vertically,while aftershocks in the north are more scattered.The focal mechanisms of the main shock and aftershocks are relatively consistent,and the P-axis orientation is consistent with the regional strain direction.There is a seismic blank area of M3.0 and above,about 3−5 km between the main shock and aftershocks.It is suggested that the energy released by the main shock rupture is concentrated in this area.Based on the earthquake location and focal mechanism of the main shock,it is inferred that the Northern Lajishan fault zone is the seismogenic structure of the main shock,and the main shock did not occur on the main fault,but on a secondary fault.The initial rupture depth and centroid depth of the main shock were 12.8 and 14.0 km,respectively.The source rupture depth may not be the main reason for the severe earthquake disaster.

Broadband ground motion simulation using a hybrid approach of the May 21, 2021 M7.4 earthquake in Maduo, Qinghai, China

In this study,the broadband ground motions of the 2021 M7.4 Maduo earthquake were simulated to overcome the scarcity of ground motion recordings and the low resolution of macroseismic intensity map in sparsely populated high-altitude regions.The simulation was conducted with a hybrid methodology,combining a stochastic high-frequency simulation with a low-frequency ground motion simulation,from the regional 1-D velocity structure model and the Wang WM et al.(2022)source rupture model,respectively.We found that the three-component waveforms simulated for specific stations matched the waveforms recorded at those stations,in terms of amplitude,duration,and frequency content.The validation results demonstrate the ability of the hybrid simulation method to reproduce the main characteristics of the observed ground motions for the 2021 Maduo earthquake over a broad frequency range.Our simulations suggest that the official map of macroseismic intensity tends to overestimate shaking by one intensity unit.Comparisons of simulations with empirical ground motion models indicate generally good consistency between the simulated and empirically predicted intensity measures.The high-frequency components of ground motions were found to be more prominent,while the low-frequency components were not,which is unexpected for large earthquakes.Our simulations provide valuable insight into the effects of source complexity on the level and variability of the resulting ground motions.The acceleration and velocity time histories and corresponding response spectra were provided for selected representative sites where no records were available.The simulated results have important implications for evaluating the performance of engineering structures in the epicentral regions of this earthquake and for estimating seismic hazards in the Tibetan regions where no strong ground motion records are available for large earthquakes.

Kinematic deformation and intensity assessment of the 2021 Maduo M_(S)7.4 earthquake in Qinghai revealed by high-frequency GNSS

Rapid acquisition of the kinematic deformation field and seismic intensity distribution of large earthquakes is crucial for postseismic emergency rescue,disaster assessment,and future seismic risk research.The advancement of GNSS observation and data processing makes it play an important role in this field,especially the high-frequency GNSS.We used the differential positioning method to calculate the 1 HZ GNSS data from 98 sites within 1000 km of the M_(S)7.4 Maduo earthquake epicenter.The kinematic deformation field and the distribution of the seismic intensity by using the peak ground velocity derived from displacement waveforms were obtained.The results show that:1)Horizontal coseismic response deformation levels ranging from 25 mm to 301 mm can be observed within a 1000 km radius from the epicenter.Coseismic response deformation on the east and west sides shows bilateral asymmetry,which markedly differs from the symmetry presented by surface rupture.2)The seismic intensity obtained through high-frequency GNSS and field investigations exhibits good consistency of the scope and orientation in the high seismic intensity area,although the former is generally slightly smaller than the latter.3)There may exist obstacles on the eastern side of the seismogenic fault.The Maduo earthquake induced a certain tectonic stress loading effect on the western Kunlun Pass-Jiangcuo fault(KPJF)and Maqin-Maqu segment,resulting in higher seismic risk in the future.

Towards fast focal mechanism inversion of shallow crustal earthquakes in the Chinese mainland

We have developed an automatic regional focal mechanism inversion system based on the Earthquake Rapid Report(ERR) system and the real-time three-component seismic waveform stream of 1 000 broadband seismic stations provided by the China Earthquake Networks Center(CENC). The system can rapidly provide a double couple solution and centroid depth within 5–15 min after receiving earthquake information from the ERR system.The data processing is triggered by earthquake information obtained from the ERR system. The system is capable of determining the focal mechanism of all shallow-depth earthquakes in the Chinese mainland with a magnitude of 5.5–6.5. It utilizes waveform data recorded by seismic stations located within 500 km from the epicenter,enabling the reporting of a focal mechanism solution within 5–15 min of an earthquake occurrence. Additionally,the system can assign a corresponding grade(A B C) to the focal mechanism solution. We processed a total of 301earthquakes that occurred from 2021 to June 2022, and after the quality control, 166 of them were selected.These selected solutions were manually checked, and 160 of them were compiled in a focal mechanism catalog.This catalog can be conveniently downloaded online via the Internet. The automatic focal mechanism solution of earthquakes in eastern China exhibits a good agreement with that provided by the Global Centroid Moment Tensor(GCMT), when available. The average Kagan angle between this catalog and GCMT is 22°, and the average difference in MWis 0.17. Furthermore, compared with GCMT, the minimum magnitude of our catalog has been reduced from approximately 5.0 to 4.0. The correlation between the centroid depth and crustal thickness in the Chinese mainland confirms the distribution of the centroid depth.

Rapid report of the 8 January 2022 M_(S)6.9 Menyuan earthquake,Qinghai,China

The M_(S)6.9 Menyuan earthquake in Qinghai Province,west China is the largest earthquake by far in 2022.The earthquake occurs in a tectonically active region,with a background b-value of 0.87 within 100 km of the epicenter that we derived from the unified catalog produced by China Earthquake Networks Center since late 2008.Field surveys have revealed surface ruptures extending 22 km along strike,with a maximum ground displacement of 2.1 m.We construct a finite fault model with constraints from In SAR observations,which showed multiple fault segments during the Menyuan earthquake.The major slip asperity is confined within 10 km at depth,with the maximum slip of 3.5 m.Near real-time back-projection results of coseismic radiation indicate a northwest propagating rupture that lasted for~10 s.Intensity estimates from the back-projection results show up to a Mercalli scale of IX near the ruptured area,consistent with instrumental measurements and the observations from the field surveys.Aftershock locations(up to January 21,2022)exhibit two segments,extending to~20 km in depth.The largest one reaches M_(S)5.3,locating near the eastern end of the aftershock zone.Although the location and the approximate magnitude of the mainshock had been indicated by previous studies based on paleoearthquake records and seismic gap,as well as estimated stressing rate on faults,significant surfacebreaching rupture leads to severe damage of the high-speed railway system,which poses a challenge in accurately assessing earthquake hazards and risks,and thus demands further investigations of the rupture behaviors for crustal earthquakes.

Possible thermal brightness temperature anomalies associated with the Lushan(China) M_s7.0 earthquake on 20 April 2013

Lushan Ms7.0 earthquake occurred in Lushan county, Ya＇an city, Sichuan province of China, on 20 April 2013, and caused 196 deaths, 23 people of missing and more than 12 thousand of people injured. In order to analyze the possible seismic brightness temperature anomalies which may be associated with Lushan earthquake, daily brightness temperature data for the period from 1 June 2011 to 31 May 2013 and the geographical extent of 25°E-35°N latitude and 98°E-108°E longitude are collected from Chinese geostationary meteorological satellite FY-2E. Continuous wavelet transform method which has good resolution both in time and frequency domains is used to analyze power spectrum of brightness temperature data. The results show that the rela- tive wavelet power spectrum （RWPS） anomalies appeared since 24 January 2013 and still lasted on 19 April. Anomalies firstly appeared at the middle part of Longmenshan fault zone and gradually spread toward the southwestern part of Longmenshan fault. Anomalies also appeared along the Xianshuihe fault since about 1 March. Eventually, anomalies gathered at the intersection zone of Longmenshan and Xianshuihe faults. The anomalous areas and RWPS ampli- tude increased since the appearance of anomalies and reached maximum in late March. Anomalies attenuated with the earthquake approaching. And eventually the earthquake occurred at the southeastern edge of anomalous areas. Lushah earthquake was the only obvious geological event within the anomalous area during the time period, so the anomalous changes of RWPS are possibly associated with the earthquake.

Studies on earthquake precursors in China:A review for recent 50 years

Since the 1960s, China has been conducting a persistent and systematic observation and monitoring experiment to falsify the hypothesis of premonitory anomalies and the predictability of earthquakes and the application of the assessment of time-dependent seismic hazard to the reduction of earthquake disaster risk. Such an endeavor, with cases of both successes and failures, provided lessons which are heuristic for the studies in earthquake science and social sustainability. This paper provides the back- ground information of such an endeavor, discussing on the achievements and space for improvements of this lane lastin~ ~ncl cantintrint7 ~ffnrl-

Annual Consultation on the Likelihood of Earthquakes in Continental China: Its Scientific and Practical Merits

Since the 1970s, Chinese seismologists have started to conduct the Annual Consultation on the Likelihood of Coming Earthquakes in the Next Year. This approach has unique scientific and practical merits either as an active response to the social needs in the situation that earthquake prediction research meets many difficulties, or as a real forward prediction test persistently conducted for 1/3 century. It is a pity that such an approach has not been well-known by international seismological community, and the scientific merits of such an endeavor is sometimes regrettably underestimated.

Co-seismic changes of well water level and volume strain meter in capital area and its vicinity,due to the Nov.14,2001 Ms8.1 Kunlun Mountain earthquake,China

The Kunlunshan Mountain Ms8.1 earthquake, occurred in Nov.14, 2001, is the first event with magnitude more than 8 in the China earthquake monitoring history, specifically at the beginning of digital techniques in precursor monitoring networks. Any investigation of recorded data on this earthquake is very important for testing the operation of the digital monitoring networks and understanding the preparation, occurrence, and adjustment of stress/strain of strong continental earthquakes. In this paper we investigated the coseismic response changes of well water level of groundwater and volume strain meter of bore hole in digital earthquake monitoring network of Capital area and its vicinity, due to the Nov.14, 2001 Ms8.1 Kunlun Mountain earthquake. The responding time, shapes or manners, amplitudes, and lasting time of well water level and strain-meters to seismic wave are studied in comparison. Then we discussed the possibility that the response changes of groundwater to strong distant earthquakes can be understood as one kind of observing evidence of stress/strain changes induced by distant earthquake.

Construction and Development of China’s Earthquake Information Release System

Focused on the current situation,monitoring system,technical management regulation,process,system composition,and information publication of the earthquake information release,we summarized the construction and development of China’s earthquake information release system and expected its future.In general,China’s earthquake information release systems is able to publish auto-results with MS≥3.0 from 1 to 3 minutes,M_S≥6.0 in global from 2 to 30 minutes,and formal results with MS≥3.0 in China from 8 to 30 minutes,MS≥6.0 in global from 20 to 60 minutes.These earthquake information is released by various channels such as short message,website,microblog,mobile application,etc.

Development of Automatic Earthquake Quick Report in China

This paper summarizes the different stages of the development of earthquake automatic quick report in China. In early stage,scientists and technicians mainly focused on the realization of automatic identification of seismic phases and automatic positioning in the network data processing system. Then,at the end of the Tenth "Five-Year Plan "project,Fujian Earthquake Agency, Guangdong Earthquake Agency, and China Earthquake Networks Center have independently developed their earthquake automatic quick report systems. Later,by taking advantage of the"multi-channel comprehensive trigger " mechanism, China Earthquake Networks Center has innovated a comprehensive trigger system for automatic earthquake quick report, whereby earthquake information can be instantly reported and presented on Weibo,Wechat,and CENC App.

Research on the Changes of Celestial Tide-generating Force and the Outgoing Long-wave Radiation before the Lushan (China) M_S7.0 Earthquake

Calculation of tidal changes reveals that the MS 7. 0 Lushan County,Sichuan,China,earthquake of April 20,2013 occurred at the minimum phase point of tidal force. It indicates that the seismogenic fault on which the tidal force acts on is of thrust type. The outgoing long-wave radiation( OLR) is the energy radiating from the Earth as infrared radiation at low energy to space. According to the tidal cycle,abnormal OLR change is analyzed based on NOAA satellite data around the whole of China before and after the earthquake. The result shows that the OLR changed evidently with the tide force change.Temporally,the change went through the course: initial OLR rise → s trengthening →reaching abnormal peak → a ttenuation → r eturning to normal; in space,the abnormal area was distributed along the Longmenshan fault and evolved as: scattering→ c onvergent→ s cattering. The process is similar to the change process of rock breaking under stress loading. It indicates that the celestial tidal force can trigger earthquakes when the tectonic stress reaches the critical break point of an active fault and the OLR anomaly is proportional to the seismic tectonic stress change. It is of practical value to combine OLR and tidal force anomaly with earthquake precursor studies.

Resource management and job scheduling of China earthquake grid experiment system: Construction of resource management and job dynamic scheduling model ProRMJS

Grid technique is taken as the third generation internet technology and resource management is the core of it. Aiming at the problems of resource management of CEDAGrid （China Earthquake Disaster Alleviation and Simulation Grid） in its preliminary construction, this paper presents a resource management and job scheduling model： ProRMJS to solve these problems. For platform supposed agreeably each computing node can provide computation service, ProRMJS uses ＂computation pool＂ to support scheduler, and then the scheduler allocates jobs dynamically according to computing capability and status of each node to ensure the stability of the platform. At the same time, ProRMJS monitors the status of job on each node and sets a time threshold to manage the job scheduling. By estimating the computing capability of each node, ProRMJS allocates jobs on demand to solve the problem of supposing each node can finish the job acquiescently. When calculating the computing capability of each node, ProRMJS allows for the various factors that affect the computing capability and then the efficiency of the platform is improved. Finally the validity of the model is verified by an example.

Comparison between different earthquake magnitudes determined by China Seismo-graph Network

By linear regression and orthogonal regression methods, comparisons are made between different magnitudes （local magnitude ML, surface wave magnitudes Ms and MsT, long-period body wave magnitude mB and short-period body wave magnitude mb） determined by Institute of Geophysics, China Earthquake Administration, on the basis of observation data collected by China Seismograph Network between 1983 and 2004. Empirical relations between different magnitudes have been obtained. The result shows that： ① As different magnitude scales reflect radiated energy by seismic waves within different periods, earthquake magnitudes can be described more objectively by using different scales for earthquakes of different magnitudes. When the epicentral distance is less than 1000 km, local magnitude ME can be a preferable scale; In case M〈4.5, there is little difference between the magnitude scales; In case 4.5〈M〈6.0, mB〉Ms, i.e., Ms underestimates magnitudes of such events, therefore, mB can be a better choice; In case M〉6.0, Ms〉mB〉mb, both mB and mb underestimate the magnitudes, so Ms is a preferable scale for determining magnitudes of such events （6.0〈M〈8.5）; In case M〉8.5, a saturation phenomenon appears in Ms, which cannot give an accurate reflection of the magnitudes of such large events; ② In China, when the epicentral distance is less than 1 000 km, there is almost no difference between ME and Ms, and thus there is no need to convert between the two magnitudes in practice; ③ Although Ms and Ms7 are both surface wave magnitudes, Ms is in general greater than Ms7 by 0.2～0.3 magnitude, because different instruments and calculation formulae are used; ④ mB is almost equal to mb for earthquakes around mB4.0, but mB is larger than mb for those of mB〉4.5, because the periods of seismic waves used for measuring mB and mb are different though the calculation formulae are the same.

Introduction to China’s Earthquake Emergency Response System

Following the M_(S)6.4 earthquake that occurred on May 21,2021 in Yangbi,Yunnan,China,the earthquake emergency response system(EERS)responded immediately.The real-time software delivered many seismic parameters that provided a preliminary assessment of the earthquake.The 24-hour on-duty staff and scientific researchers revised these parameters and produced more detailed reports to understand the cause of the earthquake and the potential damage,which provided valuable information for emergency rescue operations and earthquake situation assessment.Emergency personnel were dispatched immedia-tely to the earthquake site to observe the aftershocks,investigate the damage,and guide and assist in the relief efforts.This paper describes the EERS response to the Yangbi earthquake to demonstrate the characteristics of the system and discuss the potential for further improvement.