Strong ground motion characteristics observed in the February 6,2023 M_(W)7.7 Türkiye earthquake

Türkiye is located in a seismically active region,where the Anatolian,African,and Arabian tectonic plates converge.High seismic hazards cause the region to be struck repeatedly by major earthquakes.On February 06,2023,a devastating M_(W)7.7 earthquake struck Türkiye at 01:17 am local time(01:17 UTC).In this regard,near and far-field ground motion data within the distance of 120 km are compiled and later characterized to identify the key ground motion intensity measures.Additionally,the vertical components of ground motions were examined to capture the complete three-dimensional nature of the seismic event.Moreover,the effect of Pulse-Like(PL)and Non-Pulse-Like(NPL)ground motion on a representative RC frame structure built as per the Türkiye code was investigated.The results indicate that PL behavior was observed in both horizontal and vertical components of ground motions and PL behavior were noted both near the epicenter and at higher distances from the epicenter.Moreover,the ratio of the peak vertical acceleration to peak horizontal acceleration at certain stations was found to be close to 1.Finally,the non-linear time history analysis of the representative reinforced concrete frame structure for ground motions recorded at stations located equidistant from the epicenter,indicated that PL ground motions led to more significant damage compared to NPL ground motions.

Seismic characteristics near the epicenter of the 1303 Hongtong M=8 earthquake, Shanxi Province and its implication

In this paper, we calculated the seismic pattern of instrumental recorded small and moderate earthquakes near the epicenter of the 1303 Hongtong M=8 earthquake, Shanxi Province. According to the spatial distribution of small and moderate earthquakes, 6 seismic dense zones are delineated. Temporal distribution of ML2 earthquakes since 1970 in each seismic dense zone has been analyzed. Based on temporal distribution characteristics and historical earthquake activity, three types of seismicities are proposed. The relationship between seismic types and crustal medium is analyzed. The mechanism of three types is discussed. Finity of strong earthquake recurrence is pro-posed. Seismic hazard in mid-long term and diversity of earthquake disaster in Shanxi seismic belt are discussed.

Source rupture characteristics of the September 5,2022 Luding M_(S)6.8 earthquake at the Xianshuihe fault zone in southwest China

On September 5,2022,at Beijing time 12:52 p.m.,an M_(S)6.8 earthquake struck Luding County,GarzêTibetan Autonomous Prefecture,Sichuan Province.The epicenter of the earthquake was at the intersection of the Sichuan-Yunnan,Bayankala,and South China blocks.The tectonic background is extremely complex,and strong earthquakes occur frequently.Based on a predetermined focal location and focal mechanism solution for the earthquake,we reversed the focal depth and rupture process of the earthquake by fitting the teleseismic P and SH waves recorded by the global seismic network.The results show that the focal depth is 16 km,with the main rupture having a length of about 45 km near the epicenter,with a maximum displacement of 1.02 m.Although the rupture mainly propagates from the north–northwest(NNW)to the south–southeast(SSE)along the fault strike,there is a small-scale rupture slip zone at shallow depths in the north–northeast(NNE)direction along the epicenter of the seismogenic fault.This rupture image corresponds to the cluster distribution of aftershocks in the NNW and SSE directions starting from the epicenter,corresponding to the distribution of recorded landslides.The earthquake occurred on the Moxi fault,located in the southeastern section of the Xianshuihe fault.The major tectonic feature in this area is the southeastward movement of the Chuandian block relative to the Bayanhar block.

Tracing the Forecast of Earthquakes Based on the Seismicity Characteristics of the Chi-Chi Strong Earthquake Swarm Sequence

The data of earthquakes with M ≥3 0 during the 7 years from September 21, 1993 to September 20, 2000 recorded by the Taiwan Central Weather Bureau (CWB) show that there were 6 types of clear characteristics of seismicity during the Chi Chi strong earthquake swarm of September 21 These 6 types of characteristics are (1) foreshock types, (2) seismic gaps, (3) seismic bands, (4) clustering activity of foreshocks and signal shock, (5) quiescence before the main shock and (6) secondary aftershocks in the aftershock sequence. Using the procedures for analyzing the yearly strong earthquake tendency, further tracing based on the earthquake sequence characteristics, and taking the Chi Chi earthquake sequence as an example, tracing analysis of the earthquake tendency was attempted using the shorter time range of monthly rather than in a yearly time scale. An attempt was made to establish the procedures for tracing analysis of shallow focus earthquakes in the seismic belt of western Taiwan. It is hoped that this can provide an analystical method for approaching the short imminent time scale of seismometry based earthquake forecasting.

Subarea characteristics of earthquake types in Yunnan

Studies on the earthquake sequences and the source mechanisms of the strong earthquakes show that Yurman has more obvious subarea characteristics of earthquake type. Strike-slip seismic fault and mainshock-aftershock earthquake sequences are dominant in whole Yunnan area. Considering the ratio of non strike-slip faults and non mainshock-aftershock, Yurman area can be divided into four subareas with different characteristics, which are strike-slip mainshock-aftershock in central Yunnan （A1）, incline-slip swarm in northwestern Yunnan （A2）, strike-slip double shocks in western Yunnan （B1） and quasi-strike-slip mainshock-aftershock in southwestern Yunnan （BE）, respectively.

Analysis on Characteristics of the Hazards of the 2015 Pishan Ms 6.5 Earthquake in Xinjiang

The disaster area of the Pishan M_S6.5 earthquake in 2015 is located in the southern margin of the Tarim Basin,where the natural condition are harsh,and the economy is extremely backward.Moreover,because of a large number of residential housing with poor seismic performance in the disaster area,the damage and economic losses are serious.Since the most disaster area is located in the piedmont overflow,with poor site conditions such as shallow groundwater level and soil foundation,the magnifying effect of ground motion has a significant impact on the damage.In conclusion,we believe that investment in antiearthquake housing projects should be increased in post disaster reconstruction.Furthermore,for the north of the disaster area,with the dense population,poor conditions like soft soil foundation and poor engineering geological conditions,we recommend that in the future construction of anti-earthquake housing projects,more attention should be paid to strengthen the foundation treatment and precaution measures.

Multifractal characteristics of spatiotemporal distribution of earthquakes in intraplate and interplate regions

This paper analyzes the multifractal characteristics of spatio-temporal distribution of generalized strain release of earthquakes （GSRE） occurred in the eastern and western Chinese mainland （as an instance of intraplate region）, Taiwan region and New Zealand （as an instance of interplate region）. The results show that the multifractal characteristics of GSRE are closely related to the geodynamic environment. For the temporal distribution of strong events, the clustering feature is more evident in the interplate regions than that in the intraplate regions, while for small and moderate events, this difference is ambiguous. For the spatial distribution of strong earthquakes, the clustering feature is usually clearer in the intraplate regions than that in the interplate regions, while for small and moderate events, the case is just opposite.

The Characteristics of Earthquake Swarms in and around Jiangsu Province

This paper systematically analyzed 36 earthquake swarms in and around Jiangsu Province, summarized their characteristics and discussed the relationship between earthquske swarms and subsequent strong earthquakes. It also analyzed the judgment criteria for precursory earthquake swarms. Earthquake swarms in Jiangsu Province are concentrated in several areas. Most of them were of magnitude ML2.0～3.9. For most earthquake swarms, the number of earthquakes was less than 30. Time duration for about 55% of earthquake swarms was less than 15 days. The biggest magnitude of one earthquake swarm was not proportional to the number of earthquakes and time duration. There are 78% of earthquake swarms corresponded to the forthcoming earthquakes of M>4.6 in which there're 57% occured in one year, This shows a medium-and short-term criterion. Distance between earthquake swarm and future earthquake was distributed dispersedly. There were no earthquakes occurring in the same location as earthquake swarms. There was no good correlation between the magnitude and the corresponding rate of future earthquakes and the intensity of earthquake swarms. There was also no good correlation between the number of earthquakes in an earthquake swarm and the corresponding rate. The study also shows that it's better to use U-p or whole-combination to determine the type of earthquake swarm.

Variational characteristics of shear-wave splitting on the 2001 Shidian earthquakes in Yunnan, China

In 2001 three earthquakes occurred in Shidian in Yunnan Province, which were the MS=5.2 on April 10, the MS=5.9 on April 12 and the MS=5.3 on June 8. Based on the data from the station Baoshan of Yunnan Telemetry Digital Seismograph Network, the variational characteristics of shear-wave splitting on these series of strong earthquakes has been studied by using the systematic analysis method (SAM) of shear-wave splitting. The result shows the time delays of shear-wave splitting basically increase with earthquake activity intensifying. However the time delays abruptly decrease immediately before strong aftershocks. It accords with the stress relaxation before earthquakes, which was found recently in study on shear-wave splitting. The result suggests it is significant for reducing the harm degree of earthquakes to develop the stress-forecasting on earthquake in strong active tectonic zones and economic developed regions or big cities under the danger of strong earthquakes.

Crustal Motion Characteristics in the Eastern Margin of the Tibetan Plateau and Adjacent Regions after the Wenchuan Earthquake

The Wenchuan earthquake has altered the crustal motion characteristics in the eastern margin of the Tibetan Plateau and adjacent regions.Using discontinuous GPS survey data for 2008–2012, the velocity field for the Eurasia reference framework has been obtained, and the general trend of contemporary crustal motion after the occurrence of the Wenchuan earthquake has been studied.In addition, using the velocity field, the block movement velocity has been estimated by least-squares fitting.Furthermore, the properties and displacement rates of main faults have been obtained from the differences in velocity vectors of the blocks on both sides of the faults.The results reveal that there are no obvious changes in the general characteristics of crustal motion in this area after the Wenchuan earthquake.The earthquake mainly changed the rate of the movement of the Chuan-Qing block and caused variation in the movement direction of the South China block.The effect of the earthquake on faults is mainly reflected in variations in fault displacement velocity; there is no fundamental change in the properties of fault activity.The displacement rates of the Xianshuihe fault decreased by 3–4 mm/a, the Longmenshan fault increased by 9–10 mm/a, and the northern segment of the Anninghe fault increased by approximately 9 mm/a.Furthermore, the displacement rates of the Minjiang, Xueshan, Huya, Longquanshan, and Xinjin faults increased by 2–3 mm/a.This implies that the effects of the Wenchuan earthquake on crustal movement can mainly be observed in the Chuan-Qing, South China, and N-Chuan-Dian blocks and their internal faults, as well as the Xianshuihe and Longmenshan faults and the northern section of the Anninghe fault.The reason for this is that the Wenchuan earthquake disturbed the kinematic and dynamic balance in the region.

Frequency characteristics and far-field effect of gravity perturbation before earthquake

We used high-pass filtering and the Fourier transform to analyze tidal gravity data prior to five earthquakes from four superconducting gravity stations around the world. A stable gravitational perturbation signal is received within a few days before the earthquakes. The gravitational perturbation signal before the Wenchuan earthquake on May 12, 2008 has main frequency of 0.1–0.3 Hz, and the other four have frequency bands of 0.12-0.17 Hz and 0.06-0.085 Hz. For earthquakes in continental and oceanic plate fault zones, gravity anomalies often appear on the superconducting gravimeters away from the epicenter, whereas the stations near the epicenter record small or no anomalies. The results suggest that this kind of gravitational perturbation signals correlate with earthquake occurrence, making them potentially useful earthquake predictors. The far-field effect of the gravitational perturbation signals may reveal the interaction mechanisms of the Earth’s tectonic plates. However, owing to the uneven distribution of gravity tide stations, the results need to be further confirmed in the future.

Bi-normalized response spectral characteristics of the 1999 Chi-Chi earthquake

To develop uniform and seismic environment-dependent design spectrum,common acceleration response spectral characteristics need to be identified.In this paper,a bi-normalized response spectrum (BNRS) is proposed,which is defined as a spectrum of peak response acceleration normalized with respect to peak acceleration of the excitation plotted vs.the natural period of the system normalized with respect to the spectrum predominant period,Tp.Based on a statistical analysis of records from the 1999 Chi-Chi earthquake,the conventionally normalized response spectrum(NRS) and the BNRS are examined to account for the effects of soil conditions,epicentral distance,hanging wall and damping.It is found that compared to the NRS the BNRS is much less dependent on these factors.Finally,some simple relationships between the BNRS for a specified damping ratio and that for a damping ratio of 5%,and between the spectra predominant period and epicentral distance for different soil types are provided.

Relation between the characteristics of strong earthquake activities in Chinese mainland and the Wenchuan earthquake

This paper studies the relations between the great Wenchuan earthquake and the active-quiet periodic characteristics of strong earthquakes, the rhythmic feature of great earthquakes, and the grouped spatial distribution of Ms8.0 earthquakes in Chinese mainland. We also studied the relation between the Wenchuan earthquake and the stepwise migration characteristics of Ms≥7.0 earthquakes on the North-South seismic belt, the features of the energy releasing acceleration in the active crustal blocks related to the Wenchuan earthquake and the relation between the Wenchuan earthquake and the so called second-arc fault zone. The results can be summarized as follows： ① the occurrence of the Wenchuan earthquake was consistent with the activequiet periodic characteristics of strong earthquakes; ② its occurrence is consistent with the features of grouped occurrence of Ms8.0 earthquakes and follows the 25 years rhythm （each circulation experiences the same time） of great earthquakes; ③ the Wenchuan Ms8.0 earthquake follows the well known stepwise migration feature of strong earthquakes on the North-South seismic belt; ④ the location where the Wenchuan Ms8.0 earthquake took place has an obvious consistency with the temporal and spatial characteristic of grouped activity of Ms≥7.0 strong earthquakes on the second-arc fault zone; ⑤ the second-arc fault zone is not only the lower boundary for earthquakes with more than 30 km focal depth, but also looks like a lower boundary for deep substance movement; and ⑥ there are obvious seismic accelerations nearby the Qaidam and Qiangtang active crustal blocks （the northern and southern neighbors of the Bayan Har active block, respectively）, which agrees with the GPS observation data.

Recurrence Characteristics of Major Earthquakes in the Tangshan area,North China

The Tangshan area lies in the North China plain where an Ms 7.8 earthquake occurred in 1976, which is associated with a hidden active fault. To reveal the recurrence characteristics of major quakes in this area over a relatively long time, we have conducted a comprehensive study using geological investigations, shallow seismic exploration, boreholes, trench observations and geological dating. Five paleoearthquakes were recognized in a 6.4m-deep trench west to the Tangshan Asylum. Among them, the former three events occurred between 56.78 ＋ 4.83ka and 89.39 ~ 7.60 ka, and the fourth event occurred around 6.9 ka, respectively, and then followed by the fifth in 1976. Seven boreholes were deployed crossing the ground fissure formed by the 1976 Tangshan earthquake at the site of No. 10 Middle School, where we have identified 25 liquefaction events in the boreholes TZC6-5 and 6-7. By the comprehensive analysis of the trench, the liquefaction events from the boreholes and the depth-time curves of drill cores, we suggest a new recurrence model of major quakes in this area. It is not a constant recurring cycle since 210 ka, instead consisting of six alternating seismically quiet and active stages. Of them, stage I （〉177 ka） was a quiescent period in seismicity, stage II （from 143 ka to 177 ka） was an active one, stage III （from 102 ka to 143 ka） was quiescent again, stage IV （from 56 ka to 102 ka） had many quakes, stage V （from 6.9 ka to 56 ka） became quiet, and stage VI （from 6.9 ka to now） was the beginning of a new seismically active period.

A priliminary study on the sequence characteristics and focal mechanism solution of the Jiashi strong earthquake swarm

The sequence characteristics and focal mechanism solution of the Jiashi, Xinjiang strong earthquake swarm are analyzed and studied in this paper. The result shows that before the M S=6.6 earthquake, value h of sequence frequency attenuation coefficient was less than 1, then value h was more than 1. Before occurrence of M S6.0 earthquakes the energy is released either in a continuously strengthened way or a sharply strengthened way, and before M S5.0 earthquakes the sequence frequency shows calm. The study on the focal mechanism solution of the strong earthquake swarm shows that the source faults are mainly in a right lateral, strike slip way and the faults have characteristics of tensor shear.

Temporal distribution characteristics of GNSS ionospheric occultation data and its effects in earthquake-ionosphere anomaly detection

The temporal distribution characteristics of COSMIC occultation data are analyzed in detail, and the limitations in earthquake-ionosphere anomaly detection caused by the temporal distribution characteristics of COSMIC occultation data are discussed using the example of the Wenchuan earthquake. The results demonstrate that there is no fixed temporal resolution for COSMIC occultation data when compared with other ionospheric observation techniques. Therefore, occultation data cannot currently be independently utilized in research studies but can only be used as a complement to other ionospheric observation techniques for applications with high temporal resolution demands, such as earthquake-ionosphere anomaly detection.

New characteristics of intensity assessment of Sichuan Lushan “4.20” M_s7.0 earthquake

The post-earthquake rapid accurate assessment of macro influence of seismic ground motion is of significance for earthquake emergency relief,post-earthquake reconstruction and scientific research. The seismic intensity distribution map released by the Lushan earthquake field team of the China Earthquake Administration(CEA) five days after the strong earthquake(M7.0) occurred in Lushan County of Sichuan Ya’an City at 8:02 on April 20,2013 provides a scientific basis for emergency relief,economic loss assessment and post-earthquake reconstruction. In this paper,the means for blind estimation of macroscopic intensity,field estimation of macro intensity,and review of intensity,as well as corresponding problems are discussed in detail,and the intensity distribution characteristics of the Lushan '4.20' M7.0 earthquake and its influential factors are analyzed,providing a reference for future seismic intensity assessments.

Information characteristics of ground fluid precursors of strong continental earthquakes

It has become seismologist's common view to attach importance to the study of the characteristics about the relationship among the space distribution of precursory anomalous stations, active structure, deep rock character, and different kinds of earthquakes. In this paper, the information characteristics of ground fluid precursors are analyzed with a few examples of earthquakes. The result shows that information characteristics of ground fluid precursors mainly demonstrate, temporally stage and acceleration pattern, specially, swarm and concurrence feature. It is a key scientific problem, we propose, to give deep study on the stage and concurrence pattern for realizing the seismogenic process as well as making relatively correct prediction to the potential earthquake focus and the occurrence time.

Research on Characteristics of Focal Rupture of the Zhangbei-Shangyi Earthquake by Means of Deformation Field Obtained by Spaceborne D-INSAR

In the last ten years, the D_InSAR (Differential Interferometric Synthetic Aperture Radar) technique has proved very useful; it has been a new space observation technique with great potential. Investigating seismic focus rupture information using D_InSAR is a scientific issue to which more attention is being paid. In this paper, the basic theory of seismic focus dislocation models is discussed briefly. Based on a map of the interferometric deformation field of the Zhangbei_Shangyi earthquake from Jan.10, 1998, and applying the seismic focus dislocation model within elastic half_space medium; some geometrical and kinematical characteristics of the main seismic fault are deduced. Results were as follows: the seismic break surface of the Zhangbei_Shangyi earthquake is left_slip and thrust fault, striking in SEE_NWW 272°with dip angle 46°; rupture direction is unilateral faulting from SEE to NWW; length of rupture zone is 9km, width is 8km, and depth is 8km, the displacement vector of three directions are 290mm, 560mm and 0mm.

Seismic Damage Characteristics of the Wenchuan Great Earthquake on May 12,2008 and Suggestions for Disaster Prevention

The paper introduces the tectonic background, focal mechanism and distribution of aftershock of the Wenchuan earthquake on May 12,2008. The earthquake is considered to be the result of long-term interaction between the eastward movement of the Bayan Har Block and the Sichuan Basin. Most of the earthquake energy was released in an area （the seismic source body） 330kin long,52km wide and 20km deep over 100s. Energy release in the source body was extremely uneven, and strong ground motion in the epicenter area shows obvious asymmetrical character in the time and space scale. The high-intensity area is distributed along the source body, and the intensity distribution bears an obvious anomalous characteristic. The investigation results indicate that more than 90 percent of casualties caused by this earthquake were in the areas of intensity IX or above. Houses, schools and hospitals etc. suffered serious damage. Lifelines such as transportation, water conservation etc. also suffered significant damage. Besides, earthquake-triggered avalanches, landslides, mud-rock flows and so on were extremely serious. The tremendous earthquake disaster highlighted the deficiencies in disaster prevention and mitigation management, scientific earthquake research, technology and application of earthquake disaster prevention, and publicity of earthquake preparedness and disaster reduction.