Real-time prediction of earthquake potential damage:A case study for the January 8,2022 M_(S) 6.9 Menyuan earthquake in Qinghai,China

It is critical to determine whether a site has potential damage in real-time after an earthquake occurs,which is a challenge in earthquake disaster reduction.Here,we propose a real-time Earthquake Potential Damage predictor(EPDor)based on predicting peak ground velocities(PGVs)of sites.The EPDor is composed of three parts:(1)predicting the magnitude of an earthquake and PGVs of triggered stations based on the machine learning prediction models;(2)predicting the PGVs at distant sites based on the empirical ground motion prediction equation;(3)generating the PGV map through predicting the PGV of each grid point based on an interpolation process of weighted average based on the predicted values in(1)and(2).We apply the EPDor to the 2022 M_(S) 6.9 Menyuan earthquake in Qinghai Province,China to predict its potential damage.Within the initial few seconds after the first station is triggered,the EPDor can determine directly whether there is potential damage for some sites to a certain degree.Hence,we infer that the EPDor has potential application for future earthquakes.Meanwhile,it also has potential in Chinese earthquake early warning system.

High-precision relocation of the aftershock sequence of the January 8,2022,M_(S)6.9 Menyuan earthquake

The 2022 Menyuan M_(S)6.9 earthquake,which occurred on January 8,is the most destructive earthquake to occur near the Lenglongling(LLL)fault since the 2016 Menyuan M_(S)6.4 earthquake.We relocated the mainshock and aftershocks with phase arrival time observations for three days after the mainshock from the Qinghai Seismic Network using the double-difference method.The total length and width of the aftershock sequence are approximately 32 km and 5 km,respectively,and the aftershocks are mainly concentrated at a depth of 7-12 km.The relocated sequence can be divided into 18 km west and 13 km east segments with a boundary approximately 5 km east of the mainshock,where aftershocks are sparse.The east and west fault structures revealed by aftershock locations differ significantly.The west fault strikes EW and inclines to the south at a 71°-90°angle,whereas the east fault strikes 133°and has a smaller dip angle.Elastic strain accumulates at conjunctions of faults with different slip rates where it is prone to large earthquakes.Based on surface traces of faults,the distribution of relocated earthquake sequence and surface ruptures,the mainshock was determined to have occurred at the conjunction of the Tuolaishan(TLS)fault and LLL fault,and the west and east segments of the aftershock sequence were on the TLS fault and LLL fault,respectively.Aftershocks migrate in the early and late stages of the earthquake sequence.In the first 1.5 h after the mainshock,aftershocks expand westward from the mainshock.In the late stage,seismicity on the northeast side of the east fault is higher than that in other regions.The migration rate of the west segment of the aftershock sequence is approximately 4.5 km/decade and the afterslip may exist in the source region.

Dynamic evolution of crustal horizontal deformation before the Ms6.4 Menyuan earthquake

An Ms6.4 earthquake occurred in the Menyuan county of Qinghai Province on Jan 21, 2016.In order to recognize the development of horizontal deformation and distinguish precursory deformation anomalies, we obtained coordinates time series, velocity and strain model around the seismic zones from processing of continuous observations from 2010 and 6 times of surveying Global Positioning System(GPS) data since 2009. The results show that, before the earthquake, the eastern segmentation of the Qilian tectonic zone where the Lenglongling Fault located is in strong crustal shortening and compressional strain state with dilatational rates of -15 to -25 ppb. The Lenglongling Fault has a strike-slip rate of 3.1 mm/a and a far-field differential orthogonal rate of 7 mm/a, while differential rate is only 1.2 mm/a near the fault, which reflects its locking feature with strain energy accumulation and high seismic risks. Dynamic evolution of deformation model shows that preevent dilatational rates around the seismic zones increases from -15 ppb/a to -20 ppb/a with its center moving to the source areas. Time series of N components of G337 station,which is 13.7 km away from the Lenglongling Fault, exhibit a 5 mm/a acceleration anomaly.Time series of base-station QHME(in Menyuan) displays a reverse acceleration from the end of Sep. to Dec., 2016 when it comes to a largest deviation, and the accumulative displacement is more than 4 mm and the value reverse till the earthquake. In our results,coseismic displacement of N, E, U components in QHME site are 3.0 mm, 3.0 mm, -5.4 mm,respectively. If we profile these values onto the Lenglongling Fault, we can achieve a 1.1 mm of strike slip and 4.1 mm updip slip relative to the hanging wall.

Seismogenic structure of the 2016 Ms6.4 Menyuan earthquake and its effect on the Tianzhu seismic gap

On January 21, 2016, a strong earthquake with a magnitude of Ms6.4 occurred at Menyuan,Qinghai Province of China. In almost the same region, there was another strong earthquake happened in 1986, with similar magnitude and focal mechanism. Based on comprehensive analysis of regional active faults, focal mechanism solutions, precise locations of aftershocks, as well as GPS crustal deformation, we inferred that the Lenglongling active fault dips NE rather than SW as suggested by previous studies. Considering the facts that the 2016 and 1986 Ms6.4 Menyuan earthquakes are closely located with similar focal mechanisms, both of the quakes are on the north side of the Lenglongling Fault and adjacent to the fault, and the fault is dipping NE direction, we suggest that the fault should be the seismogenic structure of the two events. The Lenglongling Fault, as the western segment of the well-known Tianzhu seismic gap in the Qilian-Haiyuan active fault system,is in a relatively active state with frequent earthquakes in recent years, implying a high level of strain accumulation and a high potential of major event. It is also possible that the Lenglongling Fault and its adjacent fault, the Jinqianghe Fault in the Tianzhu seismic gap,are rupturing simultaneously in the future.

Vertical deformation before and after the 2022 Menyuan Ms6.9 earthquake and analysis of earthquake precursors

This study analyzed the vertical deformation before and after the 2022 Menyuan Ms6.9 earthquake in Qinghai Province,China,using leveling profiles across faults measured from Minle County in Gansu Province to Menyuan County in Qinghai Province.Our results suggest the following:(1)The amplitude of regional vertical differential motion near the Sunna-Qilian and Lenglongling faults within the Qilian Shan increased before the 2022 Menyuan earthquake.It was accompanied by the emergence of high gradient deformation zones.Deformation at the Tongziba cross-fault leveling site near the Sunan-Qilian fault was considerable.In contrast,deformation at the Daliang cross-fault leveling site near the stepover region(adjacent to the epicenter)between the Lenglongling and Tuolaishan faults was minor.After 2018,vertical deformation at the Tongziba site notably accelerated,while that at the Daliang site was insignificant.(2)After the 2022 Menyuan earthquake,140—150 mm of subsidence deformation occurred near the Daliang site,while the Tongziba site did not experience significant deformation.(3)Vertical deformation before and after the 2022 Menyuan earthquake conforms with the elastic-rebound theory,and the evolution of pre-earthquake deformation was consistent with the strike-slip fault deformation pattern at different seismogenic stages,i.e.,the relative motion near the locked fault in the late seismogenic stage gradually weakened.The characteristics of strain accumulation and release derived from the vertical deformation before and after the Menyuan MS6.9 earthquake help understand the deformation process of earthquake preparation and earthquake precursors.

Synthetic aperture radar interferometry—based coseismic deformation and slip distribution of the 2022 Menyuan MS6.9 earthquake in Qinghai,China

On January 8,2022,a 6.9 magnitude earthquake occurred in Menyuan County,Qinghai Province,with the epicenter located at the intersection of the Tuolaishan Fault and the Lenglongling Fault,which are part of the Qilian—Haiyuan fault zone.This study investigated the sliding characteristics and seismic mechanism of the earthquake to understand the activity and seismic risk of the fault on the northeastern margin of the Qinghai—Tibet Plateau.This paper analyzed Sentinel-1 synthetic aperture radar images to obtain the coseismic deformation field of the earthquake,which was then used to invert the slip distribution of the seismogenic fault and the coseismic Coulomb stress on the surrounding faults caused by the earthquake.It was found that the earthquake was primarily characterized by sinistral strike-slip movement.Along the satellite line of sight,the south wall of the fault had a maximum deformation of 0.62 m,and the north wall had a maximum deformation of 0.48 m.The coseismic slip distribution results indicated that the maximum slip of the earthquake was 4.51 m,and the moment magnitude was MW6.7.The Coulomb stress analysis showed that the 2016 Menyuan earthquake promoted the occurrence of the 2022Menyuan earthquake.

Rupture process of the January 8, 2022, Menyuan M 6.9 earthquake

After the occurrence of destructively strong earthquakes, rapid acquisition of the source rupture process can provide important reference information for post-earthquake disaster relief and aftershock trend determination.An M 6.9 earthquake occurred in Menyuan County, Qinghai Province on January 8, 2022. The epicenter is located in the seismic gap in the middle section of the Haiyuan fault belt. Such a typical strong earthquake was taken as an example to investigate the rupture process of strong earthquakes. Three days after the earthquake, the InSAR(Interferometric Synthetic Aperture Radar) coseismic deformation field was obtained by Sentinel radar, indicating that the surface ruptured obviously. The southern block of the earthquake faces towards the satellite about 95 cm along the LOS(line of sight) direction, and the northern block is away from the satellite by ~ 74 cm, consistent with the characteristic of left-lateral strike-slip motion. In this study, InSAR coseismic deformation data and farfield waveform data were used to jointly invert the earthquake rupture process, and a four-segment finite fault model was constructed by referring to the surface deformation. The inversion results show that the focal depth of the Menyuan earthquake is about 7 km, and the strike of the seismogenic fault is 89.0°, 104.0°, 119.0°and 131.0°from west to east, respectively. It is a high-dip left-lateral strike-slip earthquake event lasting about 14 s. The rupture propagation mode is a bilateral extension. The maximum slip along the fault is about 380 cm, and the seismic moment magnitude is 6.7. The surface rupture length is about 24 km, which is consistent with that measured in the field survey. The detailed seismic source model can provide basic data for the aftershock trend determination and seismic risk analysis of the adjacent active faults.

Propagation of crust deformation anomalies related to the Menyuan M_(S) 6.9 earthquake

Decoding the variation laws of the deformation field before strong earthquakes has long been recognized as an essential issue in earthquake prediction research. In this paper, the temporal and spatial distribution characteristics of deformation anomalies in the northeastern margin of the Qinghai-Tibetan Plateau before and after the Menyuan M_(S)6.9 earthquake were studied by using the Fisher statistical test method. By analyzing the characteristics of these anomalies, we found that: 1) The deformation anomalies are mainly distributed in the marginal front area of the Qinghai-Tibetan Plateau, where short-term deformation anomalies are prone to occur due to a high gradient of gravity;2) The deformation anomalies along the northeastern margin of the Qinghai-Tibetan Plateau are characterized by spatial propagation, and the migration rate is about 2.4 km/d. The propagation pattern is counterclockwise, consistent with the migration direction of M_(S)≥ 6.0 earthquakes;3) The time and location of the Menyuan earthquake are related to the group migration of earthquakes with M_(S)≥ 6.0. Finally,based on the results of gravity field variation and the theory of crust stress wave, the law of deformation anomaly distribution was discussed. We suggest that both the deformation propagation along the northeastern margin of the Qinghai-Tibetan Plateau and the earthquake migration are possibly associated with the variation of the stress field caused by subsurface mass flow.

GPS station short-term dynamic characteristics of micro displacement before Menyuan M6.4 earthquake

Continuous observation data from 24 GPS stations are selected in the area(33.0N-41.0N,95.0E-105.0E) for this study(the period is from Jan.1, 2015 to Jan.20, 2016). Three components, NS, EW and UD, of the daily solutions are filtered by the Hilberte Huang transform(HHT) with frequency band of 5.787 × 10^(-7)-7.716 × 10^(-8)Hz(20-150 days in period). And short-term dynamic characteristics of micro displacement before Menyuan M6.4 earthquake are studied by using the temporal dependencies and cross spectrum analysis. The results show that before the earthquake the horizontal undulatory motions are higher than the average level in the series data which indicate the disturbance feature of regional stress before the earthquake. Three GPS stations on Qinghai-Tibet Plateau with their setting perpendicular to the seismogenic fault have consistent movement. The increase of amplitude of the horizontal micro motion observed before the quake is conducive to the earthquake occurrence. However, we could not be sure if the undulatory motion triggered the earthquake. It is quite necessary to build more GPS continuous observation stations and optimize the monitoring network so as to improve the understanding of the shortterm dynamic crustal variation before earthquake.

Gravity variations before the Menyuan Ms6.4 earthquake

In order to study the relationship between gravity variation and Menyuan Ms6.4 earthquake, gravity variation characteristics in mid-eastern of Qilian Mountain were analyzed based on the 2012-2015 relative gravity datasets. The results indicated that the gravity changes in mid-eastern of Qilian Mountain increased gradually, while gravity changes around Menyuan remarkably. Besides, great positive-negative gravity changing gradients appeared along the Lenglongling Fault which was located at the north of Menyuan, and the 2016 Menyuan Ms6.4 earthquake occurred near the junction of positive and negative gravity changes.

Representative value of cross-fault in the northeastern margin of the Qinghai-Tibet block and case analysis of the 2016 Menyuan Ms6.4 earthquake

The equation for determining cross-fault representative value is calculated based on hanging wall and foot wall reference level surfaces. The cross-fault data reliability are analyzed base on the stability of reference datum and observation points, thereby facilitating plotting of the representative value curves after removing interference. The spatial and temporal characteristics of fault deformation abnormalities before the 2016 Menyuan Ms6.4 earthquake, as well as the fault-movement characteristics reflected by representative value, are summarized. The results show that many site trends had changed 1-3 years before the Menyuan Ms6.4 earthquake in the Qilian Fault, reflecting certain background abnormalities. The short-term abnormalities centrally had appeared in the 6 months to 1 year period before the earthquake near and in the neighborhood of the source region,demonstrating a significantly increased number of short-term abnormalities. Many sites near and in the neighborhood of the source region had strengthened inverse activities or had changed from positive to inverse activities in the most recent 2-3 years, which reflect stress-field enhancements or adjustment features.

Field source characteristic of gravity variation in Hexi region before Menyuan Ms6.4 earthquake based on the Euler deconvolution

This study adopted the Euler deconvolution method to conduct an inversion and interpretation of the depth and spatial distribution pattern of field source that lead to gravity variation. For this purpose, mobile gravity data from four periods in the Hexi region between 2011 and 2015 were obtained from an observation network. With a newly established theoretical model, we acquired the optimum inversion parameters and conducted calculation and analysis with the actual data. The results indicate that one is the appropriate value of the structure index for the inversion of the mobile gravity data. The inversion results of the actual data showed a comparable spatial distribution of the field source and a consistent structural trend with observations from the Qilian-Haiyuan Fault zone between 2011 and 2015. The distribution was in a blocking state at the epicenter of the Menyuan earthquake in 2016. Our quantitative study of the field source provides new insights into the inversion and interpretation of signals of mobile gravity variation.

Regional fault deformation characteristics before and after the Menyuan Ms6.4 earthquake

This study analyzes data regarding cross-fault deformations within the seismogenic zone of the 2016 Qinghai Menyuan Ms6.4 earthquake and its surrounding area. The results showed that the tendency anomaly sites near the epicenter had relatively long anomaly durations prior to the earthquake, while sudden-jumping anomaly sites started to increase in the middle eastern Qilian Mountains approximately a year before the earthquake and continued to increase and migrate towards the vicinity of the epicenter two to six months before the earthquake. Intensive observations a few days after the earthquake indicated that abnormal returns and turns before the earthquake were significant, but all had small amplitudes, and the coseismic effect was generally minor. In addition, the post-seismic tendency analysis of individual cross faults in the Qilian Mountain fault zone revealed an accelerating thrust tendency at all cross-fault sites in the middle Qilian Mountains after the 2008 Wenchuan Ms8.0 earthquake. This indicates that the Wenchuan mega-earthquake exerted a great impact on the dynamic environment of the northeastern margin of the Qinghai-Tibet plate and significantly enhanced the extrusion effect of the Indian plate on the middle Qilian Mountains, generating favorable conditions for the occurrence of Menyuan thrust earthquakes.

Characteristics of regional crustal deformation before 2016 Menyuan Ms6.4 earthquake

On January 21, 2016, a strong earthquake with a magnitude of Ms6.4 happened at Menyuan,Qinghai Province of China. In almost the same place, there was another strong earthquake happened in 1986, with similar magnitude and focal mechanism. In this paper, we analyze the characteristics of regional crustal deformation before the 2016 Menyuan Ms6.4 earthquake by using the data from 10 continuous Global Positioning System(GPS) stations and 74 campaign-mode GPS stations within 200 km of this event:(a) Based on the velocity field from over ten years GPS observations, a regional strain rate field is calculated. The results indicate that the crustal strain rate and seismic moment accumulation rate of the QilianHaiyuan active fault, which is the seismogenic tectonics of the event, are significantly higher than the surrounding regions. In a 20 km × 20 km area around the seismogenic region, the maximum and minimum principal strain rates are 21.5 nanostrain/a(NW-SE extension) and -46.6 nanostrain/a(NE-SW compression), respectively, and the seismic moment accumulation rates is 17.4 Nm/a. The direction of principal compression is consistent with the focal mechanism of this event.(b) Based on the position time series of the continuous GPS stations for a time-span of about 6 years before the event, we calculate the strain time series. The results show that the dilatation of the seismogenic region is continuously reduced with a "non-linear" trend since 2010, which means the seismogenic region has been in a state of compression. However, about 2-3 months before the event,both the dilatation and maximum shear strain show significant inverse trends. These abnormal changes of crustal deformation may reflect the non-linear adjustment of the stressestrain accumulation of the seismogenic region, when the accumulation is approaching the critical value of rupture.