Preseismic deformation associated with the 2014 Ms7.3 Yutian earthquake derived from GPS data

Based on analysis of the GPS data during 1999-2007,2009-2011,and 2011-2013 mainly from the Crustal Motion Observation Network of China,we obtained the GPS horizontal velocity field,the GPS strain rate field,and the profiles across the southwestern segment of the Altyn Tagh Fault zone and its adjacent regions and identified the different characteristics of horizontal crustal deformation fields and profiles during different periods. The results show that,before the February 12,2014,Ms7. 3 Yutian earthquake,the laevorotation deformation along the southwestern segment of the Altyn Tagh Fault zone increased about 3. 3 mm /a during 2011-2013,relative to that in 2009-2011,and the GPS strain rate field distributed in the southeastern segment of the Altyn Tagh Fault during 2011-2013 increased obviously. These abnormal changes may be regarded as precursors to the Ms7. 3 Yutian earthquake.

Stress triggering effect on the 2022 Honghe M_(S)5.0 earthquake with historical strong earthquakes

The 2022 Honghe M_(S)5.0 seismic event is intriguing due to its occurrence in the south of the Red River Fault,an area historically lacking seismic activities greater than M_(S)5.0.To elucidate the seismogenic mechanism and scrutinize stress-triggered interactions,we calculated co-seismic and post-seismic Coulomb stress alterations induced by nine historical seismic events(M≥6.0).The analysis reveals that these substantial seismic events provoked co-seismic stress augmentations of 1.409 bar and postseismic stress increments of 0.159 bar.Noteworthy seismic events,such as the 1833 Songming,1877Shiping,1913 Eshan,and 1970 Tonghai earthquakes,catalyzed the occurrence of the Honghe earthquake.Areas of heightened future seismic risk include the southern region of the Red River Fault and the eastern segments of the Shiping-Jianshui and Qujiang faults.Additionally,we assessed the correlation between the spatial distribution of aftershocks and the Coulomb stress shift triggered by the mainshock,taking into account the influence of calculation parameter settings.

An SPH Framework for Earthquake-Induced Liquefaction Hazard Assessment of Geotechnical Structures

Earthquake-induced soil liquefaction poses significant risks to the stability of geotechnical structures worldwide.An understanding of the liquefaction triggering,and the post-failure large deformation behaviour is essential for designing resilient infrastructure.The present study develops a Smoothed Particle Hydrodynamics(SPH)framework for earthquake-induced liquefaction hazard assessment of geotechnical structures.The coupled flowdeformation behaviour of soils subjected to cyclic loading is described using the PM4Sand model implemented in a three-phase,single-layer SPH framework.A staggered discretisation scheme based on the stress particle SPH approach is adopted to minimise numerical inaccuracies caused by zero-energy modes and tensile instability.Further,non-reflecting boundary conditions for seismic analysis of semi-infinite soil domains using the SPH method are proposed.The numerical framework is employed for the analysis of cyclic direct simple shear test,seismic analysis of a level ground site,and liquefaction-induced failure of the Lower San Fernando Dam.Satisfactory agreement for liquefaction triggering and post-failure behaviour demonstrates that the SPH framework can be utilised to assess the effect of seismic loading on field-scale geotechnical structures.The present study also serves as the basis for future advancements of the SPH method for applications related to earthquake geotechnical engineering.

Holocene activities of the Taigu fault zone, Shanxi Province, and their relations with the 1303 Hongdong M=8 earthquake

The Taigu fault zone is one of the major 12 active boundary faults of the Shanxi fault-depression system, located on the eastern boundary of the Jinzhong basin. As the latest investigation indicated, the fault zone had dislocated gully terrace of the first order, forming fault-scarp in front of the loess mesa. It has been discovered in many places in ground surface and trenches that Holocene deposits were dislocated. The latest activity was the 1303 Hongdong earthquake M=8, the fault appeared as right-lateral strike-slip with normal faulting. During that earthquake, the Taigu fault together with the Mianshan western-side fault on the Lingshi upheaval and the Huoshan pediment fault on the eastern boundary of the Linfen basin was being active, forming a surface rupture belt of 160 km in length. Moreover, the Taigu fault were active in the mid-stage of Holocene and near 7 700 aB.P. From these we learnt that, in Shanxi fault-depression system, the run-through activity of two boundary faults of depression-basins might generate great earthquake with M=8.

Preliminary analysis on characteristics of coseismic deformation associated with M_S=8.1 western Kunlunshan Pass earthquake in 2001

Based on the analysis of coseismic deformation in the macroscopic epicentral region extracted by Differential Interferometric Synthetic Aperture Radar (D-InSAR), and combined with the seismic activity, focal mechanism solutions of the earthquake and field investigation, the characteristic of coseismic deformation of MS=8.1 western Kunlunshan Pass earthquake in 2001 was researched. The study shows that its epicenter lies in the northeast side of Hoh Sai Hu; and the seismogenic fault in the macroscopic epicentral region can be divided into two central deformation fields: the west and east segments with the lengths of 42 km and 48 km, respectively. The whole fault extends about 90 km. From the distribution of interferometry fringes, the characteristic of sinistral strike slip of seismogenic fault can be identified clearly. The deformations on both sides of the fault are different with an obviously higher value on the south side. In the vicinity of macroscopic epicenter, the maximum displacement in look direction is about 288.4 cm and the minimum is 224.0 cm; the maximum sinistral horizontal dislocation of seismogenic fault near the macroscopic epicenter is 738.1 cm and the minimum is 551.8 cm.

Numerical simulation of dynamic Coulomb stress changes induced by M6.5 earthquake in Wuding, Yunnan and its relationship with aftershocks

Based on the discrete wavenumber method, we calculate the fields of dynamic Coulomb rupture stress changes and static stress changes caused by M6.5 earthquake in Wuding, and study their relationship with the subsequent after- shocks. The results show that the spatial distribution patterns of the positive region of dynamic stress peak value and static stress peak value are similarly asymmetric, which are basically identical with distribution features of aftershock. The dynamic stress peak value and the static stress in the positive region are more than 0.1 MPa and 0.01 MPa of the triggering threshold, respectively, which indicates that the dynamic and static stresses are helpful for the occurrence of aftershock. This suggests that both influences of dynamic and static stresses should be con- sidered other than only either of them when studying aftershock triggering in near field.

A Characteristic Analysis of the Dynamic Evolution of Preseismic-Coseismic-Postseismic Interferometric Deformation Fields Associated with the M 7.9 Earthquake of Mani,Tibet in 1997

By using the D-InSAR technique, we have acquired the temporal-spatial evolution images of preseismic.cosesimci-postseismic interferometric deformation fields associated with the M 7.9 earthquake of Mani, Tibet on 8 November 1997. The analysis of these images reveals the relationships between the temporal-spatial evolution features of the interferometric deformation fields and locking, rupturing, and elastic restoring of the source rupture plane, which represent the processes of strain accumulation, strain release, and postseismic restoration. The result shows that 10 months prior to the Mani event, a left-lateral shear trend appeared in the seismic area, which was in accordance with the earthquake fault in nature. The quantity of local deformation on the north wall was slightly larger than that on the south wall, and the deformation distribution area of the north wall was relatively large. With the event impending, the deformation of the south wall varied increasingly, and the deformation center shifted eastward. Two and half monthd before the event, the west side of the fault was still locked while the east side began to slide, implying that the whole fault would rupture at any moment. These features can be regarded as short-term precursors to this earthquake. Within the period from 16 April 1996 to two and half months before the earthquake, the most remarkable deformation zones appeared in the north and south walls, which were parallel to and about 40 km apart from the fault, with accumulated local displacements of 344 mm and 251 mm on the north and south walls, respectively. The south wall was the active one with larger displacements. Five months after the earthquake, the distribution feature of interferometric fringes was just opposite to that prior to the event, expressing evident right-lateral shear. The recovered displacements are -179 mm on the north wall and -79 mm on the south wall, close to the east side of the fault. However, in the area of the south wall far from the fault there still existed a trend of sinistral motion. The deformation of the north wall was small but recovered fast in a larger area, while the active south wall began to recover from the east section of the fault toward the WSW.

Diurnal characteristics of geoelectric fields and their changes associated with the Alxa Zuoqi M_S5.8 earthquake on 15 April 2015(Inner Mongolia)

In China, efforts are being made to monitor geoelectric fields through a large network of stations deployed and managed by the China Earthquake Administration. The diurnal variations in the geoelectric field waveforms were similar in the quiet magnetic periods when K〈5 （generally, K〈3 indicates a quiet time）. The arrival time points of the maxima in the geoelectric field waveforms exhibited differences in local time related to geographic longitude. The amplitude of diurnal variation was several to 16.6 mV/km and decreased with increasing latitude. Further, the amplitude of diurnal variation, which was related to seasonal changes, was larger in summer and autumn than in spring and winter. The periods of diurnal changes during quiet days were 24, 12, 8, 6, 4 hours and several minutes over large areas. Finally, the observed diurnal variations in geoelectric field prior to the Alxa Zuoqi Ms5.8 earthquake on 15 April 2015 were studied, and pronounced changes in the spectral values of the geoelectric fields were found to be associated with the Alxa Zuoqi earthquake in Inner Mongolia.

Seismic relocation,focal mechanism and crustal seismic anisotropy associated with the 2010 Yushu M_S7.1 earthquake and its aftershocks

The 2010 Yushu MsT.1 earthquake occurred in Ganzi-Yushu fault, which is the south boundary of Bayan Har block. In this study, by using double difference algorithm, the locations of mainshock （33.13°N, 96.59°E, focal depth 10.22 km） and more than 600 aftershocks were obtained. The focal mechanisms of the mainshock and some aftershocks with Ms〉3.5 were estimated by jointly using broadband velocity waveforms from Global Seismic Network （GSN） and Qinghai Seismic Network as well. The focal mechanisms and relocation show that the strike of the fault plane is about 125° （WNW-ESE）, and the mainshock is left-laterally strikeslip. The parameters of shear-wave splitting were obtained at seismic stations of YUS and L6304 by systematic analysis method of shear-wave splitting （SAM） method. Based on the parameters of shear-wave splitting and focal mechanism, the characteristics of stress field in seismic source zone were analyzed. The directions of polarization at stations YUS and L6304 are different. It is concluded that after the mainshock and the Ms6.3 aftershock on April 14, the stress-field was changed.

The ultra-low-frequency magnetic disturbances associated with earthquakes

The ultra-low-frequency （ULF） electromagnetic emission is recently recognized as one of the most promising candidates for short-term earthquake （EQ） prediction. This paper reviews previous convincing evidence on the presence of ULF emissions before three major EQs. Then, we present further statistical study on the ULF occurrence, our networks of ULF monitoring in different spatial scales in Japan and finally we present several signal processings to identify the seismogenic emissions by showing latest results for recent large EQs.

Preliminary analysis on characteristics of coseismic deformation associated with MS=8.1 western Kunlunshan Pass earthquake in 2001

Based on the analysis of coseismic deformation in the macroscopic epicentral region extracted by Differential Interferometric Synthetic Aperture Radar (D-InSAR), and combined with the seismic activity, focal mechanism solutions of the earthquake and field investigation, the characteristic of coseismic deformation of MS=8.1 western Kunlunshan Pass earthquake in 2001 was researched. The study shows that its epicenter lies in the northeast side of Hoh Sai Hu; and the seismogenic fault in the macroscopic epicentral region can be divided into two central deformation fields: the west and east segments with the lengths of 42 km and 48 km, respectively. The whole fault extends about 90 km. From the distribution of interferometry fringes, the characteristic of sinistral strike slip of seismogenic fault can be identified clearly. The deformations on both sides of the fault are different with an obviously higher value on the south side. In the vicinity of macroscopic epicenter, the maximum displacement in look direction is about 288.4 cm and the minimum is 224.0 cm; the maximum sinistral horizontal dislocation of seismogenic fault near the macroscopic epicenter is 738.1 cm and the minimum is 551.8 cm.

Earthquake damage and loss estimation with Geographic Information System

The present paper first includes a brief discussion of GIS technology. Next, the various steps in a regional earthquake damage and loss analysis are discussed, with emphasis on their implementation in the GIS environment. Lastly, a software of WorldRisk which was completed recently are presented to illustrate GIS based global earthquake damage and loss estimation.

Rock Damage Structure of the South Longmen-Shan Fault in the 2008 M8 Wenchuan Earthquake Viewed with Fault-Zone Trapped Waves and Scientific Drilling

This article is to review results from scientific drilling and fault-zone trapped waves （FZTWs） at the south Longman-Shan fault （LSF） zone that ruptured in the 2008 May 12 M8 Wenchuan earthquake in Sichuan,China.Immediately after the mainshock,two Wenchuan Fault Scientific Drilling （WFSD） boreholes were drilled at WFSD-1 and WFSD-2 sites approximately 400 m and 1 km west of the surface rupture along the Yinxiu-Beichuan fault （YBF）,the middle fault strand of the south LSF zone.Two boreholes met the principal slip of Wenchuan earthquake along the YBF at depths of 589-m and 1230-m,respectively.The slip is accompanied with a 100-200-m-wide zone consisting of fault gouge,breccia,cataclasite and fractures.Close to WFSD-1 site,the nearly-vertical slip of ～4.3-m with a 190-m wide zone of highly fractured rocks restricted to the hanging wall of the YBF was found at the ground surface after the Wenchuan earthquake.A dense linear seismic array was deployed across the surface rupture at this venue to record FZTWs generated by aftershocks.Observations and 3-D finite-difference simulations of FZTWs recorded at this cross-fault array and network stations close to the YBF show a distinct low-velocity zone composed by severely damaged rocks along the south LSF at seismogenic depths.The zone is several hundred meters wide along the principal slip,within which seismic velocities are reduced by ～30-55％ from wall-rock velocities and with the maximum velocity reduction in the ～200-m-wide rupture core zone at shallow depth.The FZTW-inferred geometry and physical properties of the south LSF rupture zone at shallow depth are in general consistent with the results from petrological and structural analyses of cores and well log at WFSD boreholes.We interpret this remarkable low-velocity zone as being a break-down zone during dynamic rupture in the 2008 M8 earthquake.We examined the FZTWS generated by similar earthquakes before and after the 2008 mainshock and observed that seismic velocities within fault core zone was reduced by ～10％ due to severe damage of fault rocks during the M8 mainshock.Scientific drilling and locations of aftershocks generating prominent FZTWs also indicate rupture bifurcation along the YBF and the Anxian-Guangxian fault （AGF）,two strands of the south LSF at shallow depth.A combination of seismic,petrologic and geologic study at the south LSF leads to further understand the relationship between the fault-zone structure and rupture dynamics,and the amplification of ground shaking strength along the low-velocity fault zone due to its waveguide effect.

Comparison of the earthquake detection abilities of PhaseNet and EQTransformer with the Yangbi and Maduo earthquakes

PhaseNet and EQTransformer are two state-of-the-art earthquake detection methods that have been increasingly applied worldwide.To evaluate the generaliz-ation ability of the two models and provide insights for the development of new models,this study took the sequences of the Yunnan Yangbi M6.4 earthquake and Qinghai Maduo M7.4 earthquake as examples to compare the earthquake detection effects of the two abovementioned models as well as their abilities to process dense seismic sequences.It has been demonstrated from the corresponding research that due to the differences in seismic waveforms found in different geographical regions,the picking performance is reduced when the two models are applied directly to the detection of the Yangbi and Maduo earthquakes.PhaseNet has a higher recall than EQTransformer,but the recall of both models is reduced by 13%-56%when compared with the results rep-orted in the original papers.The analysis results indicate that neural networks with deeper layers and complex structures may not necessarily enhance earthquake detection perfor-mance.In designing earthquake detection models,attention should be paid to not only the balance of depth,width,and architecture but also to the quality and quantity of the training datasets.In addition,noise datasets should be incorporated during training.According to the continuous waveforms detected 21 days before the Yangbi and Maduo earthquakes,the Yangbi earthquake exhibited foreshock,while the Maduo earthquake showed no foreshock activity,indicating that the two earthquakes’nucleation processes were different.

Probing the lower ionospheric perturbations associated with earthquakes by means of subionospheric VLF/LF propagation

There have been reports for many years that the ionosphere is very sensitive to seismic effects, and the detection of ionospheric perturbations associated with earthquakes （EQs） attracts a lot of attention as a very promising candidate for short-term EQ prediction. In this review we present a possible use of VLF/LF （very low frequency （3-30 kHz）/low frequency （30-300 kHz）） radio sounding of seismo-ionospheric perturbations. In order to avoid the overlapping with my own previous reviews, we first show some pioneering results for the Kobe EQ and we try to present the latest results including the statistical evidence on the correlation between the VLF/LF propagation anomalies （ionospheric perturbations） and EQs （especially with large magnitude and with shallow depth）, medium-distance （6-8 Mm） propagation anomalies, the fluctuation spectra of subionospheric VLF/LF data （the effect of atmospheric gravity waves, the effect of Earth＇s tides, etc.）, and the mechanism of lithosphere-atmosphere-ionosphere coupling. Finally, we indicate the present situation of this kind of VLF/LF activities going on in different parts of the globe and we suggest the importance of international collaboration in this seismo-electromagnetic study.

Temporal gravity changes before the 2008 Yutian Ms7.3 earthquake

Based on the data of the repeated gravity observation network in Chinese mainland since 1998, we analyzed the temporal changes of regional gravity field before the 2008 Yutian Ms7.3 earthquake. The result shows some mid-to-long term （two to ten years） changes during the earthquake＇ s preparation. Notable fea- tures are a gravity increase lasting several years and a relatively large-scaled gradient zone of gravity change, the former indicating a continuous energy accumulation and the latter a possible location of seismic rupture. These gravity changes showed a trend of increase-accelerated increase-decelerated increase, similar to that of the Tangshan Ms7.8 earthquake in 1976. The maximum accumulated gravity change related to the earthquake reached 200 × 10 -8 ms -2.

Different earthquake patterns for two neighboring fault segments within the Haiyuan Fault zone

Characteristic slip and characteristic earthquake models have been proposed for several decades. Such models have been supported recently by high-resolution offset measurements. These models suggest that slip along a fault recurs via similarly sized, large earthquakes. The inter-event strain accumulation rate(ratio of earthquake slip and preceding interseismic time period) is used here to test the characteristic earthquake model by linking the slip and timing of past earthquakes on the Haiyuan Fault. We address how the inter-event strain accumulation rate varies over multiple seismic cycles by combining paleoearthquake studies with high-resolution airborne light detection and ranging(Li DAR) data to document the timing and size of paleoearthquake displacements along the western and middle segments of the Haiyuan Fault. Our observations encompass 5 earthquake cycles. We find significant variations over time and space along the Haiyuan Fault. We observe that on the middle segment of the Haiyuan Fault the rates slow down or increase as an anticorrelated function of the rates of preceding earthquakes. Here, we propose that the inter-event strain accumulation rates on the middle segment of the Haiyuan Fault are oscillating both spatially and temporally. However, along the western segment, the inter-event strain accumulation rate is both spatially and temporally steady, which is in agreement with quasi-periodic and slip-predictable models. Finally,we propose that different fault segments within a single fault zone may behave according to different earthquake models.

Rapid repair of severely earthquake-damaged bridge piers with flexural-shear failure mode

An experimental study was conducted to investigate the feasibility of a proposed rapid repair technique for severely earthquake-damaged bridge piers with flexural-shear failure mode. Six circular pier specimens were first tested to severe damage in flexural-shear mode and repaired using early-strength concrete with high-fluidity and carbon fiber reinforced polymers （CFRP）. After about four days, the repaired specimens were tested to failure again. The seismic behavior of the repaired specimens was evaluated and compared to the original specimens. Test results indicate that the proposed repair technique is highly effective. Both shear strength and lateral displacement of the repaired piers increased when compared to the original specimens, and the failure mechanism of the piers shifted from flexural-shear failure to ductile flexural failure. Finally, a simple design model based on the Seible formulation for post-earthquake repair design was compared to the experimental results. It is concluded that the design equation for bridge pier strengthening before an earthquake could be applicable to seismic repairs after an earthquake if the shear strength contribution of the spiral bars in the repaired piers is disregarded and 1.5 times more FRP sheets is provided.

Holocene activities of the Taigu fault zone,Shanxi Province, and their relations with the 1303 Hongdong M=8 earthquake

No abstract available

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.