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.

Research on the Extraction of OLR Anomaly Prior to Ms 7.5 Sand Point,Alaska Earthquake based on IPI Method

Based on the understanding that the seismic fault system is a nonlinear complex system,Rundle(1995)introduced the nonlinear threshold system used in meteorology to analyze the ocean-atmosphere interface and the El Ni?o Southern Oscillation into the study of seismic activity changes,and then proposed the PI method(Rundle et al.,2000a,b).Wu et al.(2011)modified the Pattern Informatics Method named MPI to extract the ionospheric anomaly by using data from DEMETER satellites which is suitable for 1–3 months short-term prediction.

An envelope-based machine learning workflow for locating earthquakes in the southern Sichuan Basin

The development of machine learning technology enables more robust real-time earthquake monitoring through automated implementations. However, the application of machine learning to earthquake location problems faces challenges in regions with limited available training data. To address the issues of sparse event distribution and inaccurate ground truth in historical seismic datasets, we expand the training dataset by using a large number of synthetic envelopes that closely resemble real data and build an earthquake location model named ENVloc. We propose an envelope-based machine learning workflow for simultaneously determining earthquake location and origin time. The method eliminates the need for phase picking and avoids the accumulation of location errors resulting from inaccurate picking results. In practical application, ENVloc is applied to several data intercepted at different starting points. We take the starting point of the time window corresponding to the highest prediction probability value as the origin time and save the predicted result as the earthquake location. We apply ENVloc to observed data acquired in the southern Sichuan Basin, China, between September 2018 and March 2019. The results show that the average difference with the catalog in latitude, longitude, depth, and origin time is 0.02°,0.02°, 2 km, and 1.25 s, respectively. These suggest that our envelope-based method provides an efficient and robust way to locate earthquakes without phase picking, and can be used in earthquake monitoring in near-real time.

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.

Quantitative data about active tectonics and possible locations of strong earthquakes in the future in the northwestern Beijing

Deterministic, probabilistic and composite-grading methods are used to get the possible locations of strong earth-quakes in the future in Norwest Beijing and its vicinity based on the quantitative data and their accuracy about active tectonics in the research area and by ordering, some questions in the results are also discussed. It shows that the most dangerous fault segments for strong earthquakes in the future include: segments B and A of the southern boundary fault of the Yangyuan basin, the southern boundary fault of the Xuanhua basin, the east segment of the southern Huaian fault and the east segment of the northern YanggaoTianzhen fault. The most dangerous area is YangyuanShenjing basin, the second one is TianzhenHuaianXuanhua basin and the third dangerous areas are WanquanZhangjiakou and northeast of Yuxian to southwest of Fanshan.

Rupture process of the 2011 Tohoku earthquake from the joint inversion of teleseismic and GPS data

Teleseismic and GPS data were jointly inverted for the rupture process of the 2011 Tohoku earthquake. The inversion results show that it is a bilateral rupture event with an average rupture velocity less than 2.0 km/s along the fault strike direction. The source rupture process consists of three sub-events, the first oc- curred near the hypocenter and the rest two ruptured along the up-dip direction and broke the sea bed, causing a maximum slip of about 30 m. The large-scale sea bed breakage may account for the tremendous tsunami disaster which resulted in most of the death and missing in this mega earthquake.

Source time functions of the Gonghe，China earthquake retrieved from long－period digital waveform data using empirical Green＇s function technique

An earthquake of Ms= 6, 9 occurred at the Gonghe, Qinghai Province, China on April 26, 1990. Three larger aftershocks took place at the same region, Ms= 5. 0 on May 7, 1990, Ms= 6. 0 on Jan. 3, 1994 and Ms= 5. 7on Feb. 16, 1994. The long-period recordings of the main shock from China Digital Seismograph Network (CDSN) are deconvolved for the source time functions by the correspondent0 recordings of the three aftershocks asempirical Green's functions (EGFs). No matter which aftershock is taken as EGF, the relative source time functions (RSTFs) Obtained are nearly identical. The RSTFs suggest the Ms= 6. 9 event consists of at least two subevents with approximately equal size whose occurrence times are about 30 s apart, the first one has a duration of 12 s and a rise time of about 5 s, and the second one has a duration of 17 s and a rise time of about & s. COmParing the RSTFs obtained from P- and SH-phases respectively, we notice that those from SH-phases are a slightly more complex than those from p-phases, implying other finer subevents exist during the process of the main shock. It is interesting that the results from the EGF deconvolution of long-Period way form data are in good agreement with the results from the moment tensor inversion and from the EGF deconvolution of broadband waveform data. Additionally, the two larger aftershocks are deconvolved for their RSTFs. The deconvolution results show that the processes of the Ms= 6. 0 event on Jan. 3, 1994 and the Ms= 5. 7 event on Feb. 16,1994 are quite simple, both RSTFs are single impulses.The RSTFs of the Ms= 6. 9 main shock obtained from different stations are noticed to be azimuthally dependent, whose shapes are a slightly different with different stations. However, the RSTFs of the two smaller aftershocks are not azimuthally dependent. The integrations of RSTFs over the processes are quite close to each other, i. e., the scalar seismic moments estimated from different stations are in good agreement. Finally the scalar seismic moments of the three aftershocks are compared. The relative scalar seismic moment Of the three aftershocks deduced from the relative scalar seismic moments of the Ms=6. 9 main shock are very close to those inverted directly from the EGF deconvolution. The relative scalar seismic moment of the Ms =6. 9 main shock calculated using the three aftershocks as EGF are 22 (the Ms= 6. 0 aftershock being EGF), 26 (the Ms= 5. 7 aftershock being EGF) and 66 (the Ms= 5. 5 aftershock being EGF), respectively. Deducingfrom those results, the relative scalar sesimic moments of the Ms= 6. 0 to the Ms= 5. 7 events, the Ms= 6. 0 tothe Ms= 5. 5 events and the Ms= 5. 7 to the Ms= 5. 5 events are 1. 18, 3. 00 and 2. 54, respectively. The correspondent relative scalar seismic moments calculated directly from the waveform recordings are 1. 15, 3. 43, and 3. 05.

Anomaly detection of earthquake precursor data using long short-term memory networks

Earthquake precursor data have been used as an important basis for earthquake prediction.In this study,a recurrent neural network(RNN)architecture with long short-term memory(LSTM)units is utilized to develop a predictive model for normal data.Furthermore,the prediction errors from the predictive models are used to indicate normal or abnormal behavior.An additional advantage of using the LSTM networks is that the earthquake precursor data can be directly fed into the network without any elaborate preprocessing as required by other approaches.Furthermore,no prior information on abnormal data is needed by these networks as they are trained only using normal data.Experiments using three groups of real data were conducted to compare the anomaly detection results of the proposed method with those of manual recognition.The comparison results indicated that the proposed LSTM network achieves promising results and is viable for detecting anomalies in earthquake precursor data.

Source parameters of the Gonghe,Qinghai Province,China,earthquake from inversion of digital broadband waveform data

An earthquake of M S=6.9 occurred in Gonghe County, Qinghai Province, China on April 26, 1990.This earthquake was followed by three larger aftershocks of M S=5.5 on May 7, 1990, M S=6.0 on Jan.3, 1994, and M S=5.7 on Feb.16, 1994, consecutively. The moment tensors of these earthquakes as function of time were obtained by the technique of moment tensor inversion in frequency domain . The results inverted indicate that these earthquakes had a very similar focal mechanism of predominantly reverse faulting on a plane striking NWW, dipping to SSW.The scalar seismic moments of these earthquakes are M 0=9.4×10 18 Nm for the M S=6.9 event, 8.0×10 16 Nm for the M S=5.5 event, 4.9×10 17 Nm for the M S =6.0 event and 2.9×10 17 Nm for the M S=5.7 event, respectively. The results inverted also show that the source processes of these events were significantly different. The main shock had a very complex process, consisting of two distinct sub events with comparable sizes. The first sub event occurred in the first 12s, having a seismic moment of 4.7×10 18 Nm, and the second one continued from 31s to 41s, having a seismic moment of 2.5×10 18 Nm. In addition, a much smaller sub event, having a seismic moment of about 2.1×10 18 Nm, may exist in the interval of 12 s and 31 s, In contrast, the source processes of the three aftershocks are quite simple. The source time function of each of aftershocks is a single impulse, suggestting that each of aftershocks consists of a mainly uninterrupted rupture. The rise times and total rupture durations are 4 s and 11 s for the M S=5.5 event, 6 s and 16 s for the M S= 6.0 event and 6 s and 13 s for the M S=5.7 event, respectively.

Research on completeness of earthquake data in the Chinese mainland（Ⅱ）──The regional distribution of the beginning years of basically complete earthquake data

Based on the concrete conditions of earthquake data in the west of China, East China and SOuth China, we studied the completeness of data in these regions by suitable methods to local conditions. Otherwise, we roughly estimated monitoring capability of local networks in China since 1970 and some outlying regions where the data is lack. Finally, we gave the regional distribution of the beginning years since which the data for different magnitude intervals are largely complete in the Chinese mainland.

Resolving co- and early post-seismic slip variations of the 2021 MW 7.4 Madoi earthquake in east Bayan Har block with a block-wide distributed deformation mode from satellite synthetic aperture radar data

On 21 May 2021(UTC),an MW 7.4 earthquake jolted the east Bayan Har block in the Tibetan Plateau.The earthquake received widespread attention as it is the largest event in the Tibetan Plateau and its surroundings since the 2008 Wenchuan earthquake,and especially in proximity to the seismic gaps on the east Kunlun fault.Here we use satellite interferometric synthetic aperture radar data and subpixel offset observations along the range directions to characterize the coseismic deformation of the earthquake.Range offset displacements depict clear surface ruptures with a total length of~170 km involving two possible activated fault segments in the earthquake.Coseismic modeling results indicate that the earthquake was dominated by left-lateral strike-slip motions of up to 7 m within the top 12 km of the crust.The well-resolved slip variations are characterized by five major slip patches along strike and 64%of shallow slip deficit,suggesting a young seismogenic structure.Spatial-temporal changes of the postseismic deformation are mapped from early 6-day and 24-day InSAR observations,and are well explained by time-dependent afterslip models.Analysis of Global Navigation Satellite System(GNSS)velocity profiles and strain rates suggests that the eastward extrusion of plateau is diffusely distributed across the east Bayan Har block,but exhibits significant lateral heterogeneities,as evidenced by magnetotelluric observations.The block-wide distributed deformation of the east Bayan Har block along with the significant co-and post-seismic stress loadings from the Madoi earthquake imply high seismic risks along regional faults,especially the Tuosuo Lake and Maqên-Maqu segments of the Kunlun fault that are known as seismic gaps.

Source complexity of the 2016 M_W7.8 Kaikoura (New Zealand) earthquake revealed from teleseismic and InSAR data

On November 13, 2016, an MW7.8 earthquake struck Kaikoura in South Island of New Zealand. By means of back-projection of array recordings, ASTFs-analysis of global seismic recordings, and joint inversion of global seismic data and co-seismic In SAR data, we investigated complexity of the earthquake source. The result shows that the 2016 MW7.8 Kaikoura earthquake ruptured about 100 s unilaterally from south to northeast(~N28°–33°E), producing a rupture area about 160 km long and about 50 km wide and releasing scalar moment 1.01×1021 Nm. In particular, the rupture area consisted of two slip asperities, with one close to the initial rupture point having a maximal slip value ~6.9 m while the other far away in the northeast having a maximal slip value ~9.3 m. The first asperity slipped for about 65 s and the second one started 40 s after the first one had initiated. The two slipped simultaneously for about 25 s.Furthermore, the first had a nearly thrust slip while the second had both thrust and strike slip. It is interesting that the rupture velocity was not constant, and the whole process may be divided into 5 stages in which the velocities were estimated to be 1.4 km/s, 0 km/s, 2.1 km/s, 0 km/s and 1.1 km/s, respectively. The high-frequency sources distributed nearly along the lower edge of the rupture area, the highfrequency radiating mainly occurred at launching of the asperities, and it seemed that no high-frequency energy was radiated when the rupturing was going to stop.

Estimation of the 2001 Kunlun earthquake fault slip from GPS coseismic data using Hori’s inverse method

The Hori＇s inverse method based on spectral decomposition was applied to estimate coseismic slip distribution on the rupture plane of the 14 November 2001 Ms8.1 Kunlun earthquake based on GPS survey results. The inversion result shows that the six sliding models can be constrained by the coseismic GPS data. The established slips mainly concentrated along the eastern segment of the fault rupture, and the maximum magnitude is about 7 m. Slip on the eastern segment of the fault rupture represents as purely left-lateral strike-slip. Slip on the western segment of the seismic rupture represents as mainly dip-stip with the maximum dip-slip about 1 m. Total predicted scalar seismic moment is 5.196× 10^2° N.m. Our results constrained by geodetic data are consistent with seismological results.

Detection and interpretation of the Earth's free oscillations excited by the great Sumatra-Andaman earthquake with GGP station data

The mode serials of the Earth’s free oscillation provide some important information on the Earth’s deep structure and superconducting gravimeters （SG） can investigate the phenomena of the Earth’s free oscillations with high accuracy. The great Sumatra-Andaman earthquake fully excited the Earth’s free oscillations and these signals were perfectly recorded by five superconducting gravimeters in the globe. After the pre-treatment and spectral analysis on the SG observation data, we obtained the experimented mode serials of the Earth’s free oscillations consisting of 147 modes with GGP station data. These observed modes were themselves some new important data for the study of the Earth’s deep structure. On the basis of the discussions on some checked inner-core-sensitive modes, we distinguished three layers from the inner core, and the boundary of the upper layer was compatible with the formerly known transition zone in the inner core based on seismic body waves and supported that there were the hemispherical variation and very lower shear velocity zone in the lower inner core.

Prompt seismic data sharing for the 2021 Maduo earthquake in Qinghai province, China

An M_(S)7.4 earthquake struck west China in Maduo county,Guoluo prefecture,Qinghai province on May 22,2021,at 2:04 Beijing time(18:04 UTC on May 21,2021),which broke the quiet period of Chinese mainland for 1382 days without earthquakes of magnitude 7 or higher.The analysis of the seismic data sequence would play an important role in the in-depth study of the Maduo earthquake and the Bayan Har block.The Institute of Geophysics,China Earthquake Administration(CEA),compiled observation data recorded through 57 broadband seismometers within 500 km of the earthquake epicenter and intended to share for further researches in earthquake science community.The shared dataset included waveforms of the event and its sequence with magnitudes of 3.0 or higher that occurred between May 22-31,2021 with a sampling rate of 100 sps along with the continuous waveforms of 20 Hz and 100 Hz.Additionally,the seismic instrument response files also were shared.The event and continuous waveform records could be downloaded by submitting a request through the web platform of the Earthquake Science Data Center of the Institute of Geophysics,CEA(www.esdc.ac.cn).

Co-seismic fault geometry and slip distribution of the 26 December 2004, giant Sumatra–Andaman earthquake constrained by GPS, coral reef, and remote sensing data

We analyze co-seismic displacement field of the 26 December 2004, giant Sumatra–Andaman earthquake derived from Global Position System observations,geological vertical measurement of coral head, and pivot line observed through remote sensing. Using the co-seismic displacement field and AK135 spherical layered Earth model, we invert co-seismic slip distribution along the seismic fault. We also search the best fault geometry model to fit the observed data. Assuming that the dip angle linearly increases in downward direction, the postfit residual variation of the inversed geometry model with dip angles linearly changing along fault strike are plotted. The geometry model with local minimum misfits is the one with dip angle linearly increasing along strike from 4.3oin top southernmost patch to 4.5oin top northernmost path and dip angle linearly increased. By using the fault shape and geodetic co-seismic data, we estimate the slip distribution on the curved fault. Our result shows that the earthquake ruptured ＊200-km width down to a depth of about 60 km.0.5–12.5 m of thrust slip is resolved with the largest slip centered around the central section of the rupture zone78N–108N in latitude. The estimated seismic moment is8.2 9 1022 N m, which is larger than estimation from the centroid moment magnitude（4.0 9 1022 N m）, and smaller than estimation from normal-mode oscillation data modeling（1.0 9 1023 N m）.

SeisGuard: A Software Platform to Establish Automatically an Earthquake Forecasting Model

SeisGuard, a system for analyzing earthquake precursory data, is a software platform to search for earthquake precursory information by processing geophysical data from different sources to establish automatically an earthquake forecasting model. The main function of this system is to analyze and process the deformation, fluid, electromagnetic and other geophysical field observing data from ground-based observation, as well as space-based observation. Combined station and earthquake distributions, geological structure and other information, this system can provide a basic software platform for earthquake forecasting research based on spatiotemporal fusion. The hierarchical station tree for data sifting and the interaction mode have been innovatively developed in this SeisGuard system to improve users’ working efficiency. The data storage framework designed according to the characteristics of different time series can unify the interfaces of different data sources, provide the support of data flow, simplify the management and usage of data, and provide foundation for analysis of big data. The final aim of this development is to establish an effective earthquake forecasting model combined all available information from ground-based observations to space-based observations.

Lithospheric stress in Mongolia,from earthquake source data

Lithospheric stress in Mongolia has been studied using mechanisms of 84 M_(LH)≥ 4 earthquakes that occurred in the 20 th century and instrumental seismic moments of 17,375 M_(LH)≥2.5 events recorded between 1970 and 2000.The M_(LH)≥ 3.5 earthquakes mostly have strike-slip mechanisms in southern and central Mongolia,with frequent reverse-slip motions in the west and normal slip in the north,especially,in the area of Lake Hovsgol.The principal stresses are,respectively,S_H>S_v>S_h in the center and in the south;high horizontal compression with S_H>S_h>S_v in the west;and a heterogeneous stress pattern with S_v>S_H>S_h in the north.According to seismic moments of M_(LH)=2.5 events,oblique slip generally predominates over the territory,at S_v≈S_H>>S_h,while frequent strike slip motions in the west record high horizontal compression(S_H>S_v>S_h).Earthquake mechanisms show the principal horizontal compression S_H to be directed W-E in the east,NE-SW in the central and Gobi-Altay regions,and approximately N-S in the west of Mongolia.The patterns of principal lithospheric stresses in the territory of Mongolia have undergone three events of dramatic change for a few recent decades,and these events were synchronous with three similar events in the Baikal rift system(BRS):in the latest 1960 s,latest 1970 s to earliest 1980 s,and in the latest 1980 s to earliest 1990 s.The seismicity of Mongolia has been controlled by superposition of variable stresses associated with rifting activity pulses in the neighbor BRS on the background of quasi-stationary super-regional compression.

Research on the completeness of earthquake data in the Chinese mainland（I）──North China

In terms of the temporal-spatial distribution features of earthquakes, we study the completeness of historical data in North China where there is the most plenty historical data and with the longest record history by some meth ods of analysis and comparison. The results are obtained for events with Ms≥4 are largely complete since 1484 in North China (except Huanghai sea region and remote districts, such as Nei Mongol Autonomous region), but quakes with Ms≥6 are largely complete since 1291 in the middle and lower reaches of the Yellow River.