Recurrence Period Of Earthquakes Research Articles

The soil characterization of the region between the Maltepe-Beykoz Fault and the Marmara Sea in İstanbul (Türkiye) with the integrated HVSR (Nakamura technique) and MASW method

Completing the earthquake recurrence period of the Marmara segment, one of the two seismic gaps of the northern Anatolian fault zone, necessitates earthquake hazard studies for Istanbul, considering the population density. This study focuses on determining the soil properties of the study area in the Maltepe district of Istanbul. The Maltepe, with its large population density, stands very close to this fault zone and is vulnerable to earthquake damage. The soil properties such as Vs30, dominant period (T0), and amplification ratio (A0) were determined with the MASW from surface wave analysis methods at 48 points and the HVSR approach of microtremor analysis methods at 26 points. These point-based properties were mapped in the GIS environment, and spatial distribution maps were prepared. In addition, seismic vulnerability (Kg) and effective shear strain (γe) calculations for different acceleration values were carried out to detect deformation-failure on the surface. It was understood from the maps and the 2D cross-sections produced to examine the lateral and vertical changes that the soil conditions in the study area developed under the control of the Maltepe Beykoz fault (MBF). Accordingly, the two sides of the MBF lineament were determined with different geophysical outputs by their different geological origins. Namely, the alluvial part in the coastal part was defined by low Vs30, high period, and Kg values; on the contrary, the more rigid parts located at high elevations were described by relatively high Vs30, low period, and Kg values. In addition, it was understood that the deltaic sediments spread loosely and undulated in the alluvium at the SE part of the MBF lineament. These results obtained in the study are significant for predicting disaster damages and taking precautions before disasters. In addition, the scientific data potential of the outcomes of this study will make future studies, which are carried out to determine other parameters to be used during the taking of the precautions, more accessible.

Fractal Dimension Analysis and Earthquake Repeated Period Estimation in the Southern Part of Sumatra Subduction Zone (Bengkulu-Lampung-Sunda Segment)

DOI:10.17014/ijog.9.3.383-394An earthquake seismicity parameter study has been conducted in the southern part of the Sumatra Subduction Zone (SSZ) for the period of 1919 to 2019 with a hypocentre depth of 120 km and magnitude of ≥4Mw. The researched area is divided into three segments, Bengkulu, Lampung, and Sunda segments, respectively. This study aims to evaluate the seismicity parameters in the form of a-value, b-value, fractal dimension, and probabilities of earthquake recurrence period. Frequency-magnitude correlation statistical approach introduced by Gutenberg-Richter was used to calculate the seismicity parameters based on catalogue data obtained from USGS. An a-value variation of 5.11±1.84 to 5.85±2.46 obtained indicates the most dominant seismic intensity. b-value of 0.69±0,.17 to 0.83±0.35 correlates with high-stress levels, the level of spatial heterogeneity on the SFZ, and the probabilities of bigger earthquakes in the future. The calculation of fractal dimension of 1.4±0.33 to 1.7±0.71 indicates an earthquake distribution pattern was caused by a single fracture zone along the southern part of SSZ. The fracture zone is located on the left and right sides of the southern part of SSZ, which may not have been connected. In addition, the calculation result of earthquake recurrence period with magnitude ≥6.5Mw indicates that there will be an 5 - 6 earthquake event in the Bengkulu segment, 2 - 3 event in the Lampung segment, and 1 - 2 event in the Sunda segment, while the probabilities of an earthquake with magnitude ≥7.5Mw along the southern part of SSZ is 1 - 2 times.

Complex Slip Distribution of the 2021 Mw 7.4 Maduo, China, Earthquake: An Event Occurring on the Slowly Slipping Fault

Abstract The 21 May 2021 Maduo earthquake occurred on the Kunlun Mountain Pass–Jiangcuo fault (KMPJF), a seismogenic fault with no documented large earthquakes. To probe its kinematics, we first estimate the slip rates of the KMPJF and Tuosuo Lake segment (TLS, ∼75 km north of the KMPJF) of the East Kunlun fault (EKLF) based on the secular Global Positioning System (GPS) data using the Markov chain Monte Carlo method. Our model reveals that the slip rates of the KMPJF and TLS are 1.7 ± 0.8 and 7.1 ± 0.3 mm/yr, respectively. Then, we invert high-resolution GPS and Interferometric Synthetic Aperture Radar observations to decipher the fault geometry and detailed coseismic slip distribution associated with the Maduo earthquake. The geometry of the KMPFJ significantly varies along strike, composed of five fault subsegments. The most slip is accommodated by two steeply dipping fault segments, with the patch of large sinistral slip concentrated in the shallow depth on a simple straight structure. The released seismic moment is ∼1.5×1020 N·m, equivalent to an Mw 7.39 event, with a peak slip of ∼9.3 m. Combining the average coseismic slip and slip rate of the main fault, an earthquake recurrence period of ∼1250−400+1120 yr is estimated. The Maduo earthquake reminds us to reevaluate the potential of seismic gaps where slip rates are low. Based on our calculated Coulomb failure stress, the Maduo earthquake imposes positive stress on the Maqin–Maqu segment of the EKLF, a long-recognized seismic gap, implying that it may accelerate the occurrence of the next major event in this region.

Joint‐Rupture Pattern and Newly Generated Structure of Fault Intersections on the Northern Margin of the Linhe Basin, Northwestern Ordos Block, China

AbstractThe activity of major active faults around the Ordos Block is of great interest to seismologists, as at least fourM ≥ 8 earthquakes have been recorded. However, the Linhe Basin, which has the thickest Cenozoic sediments, has no record of large earthquakes. Does this basin have the structural conditions required for large earthquakes? The northern boundary fault of the Linhe Basin is composed of the NE‐striking Langshan piedmont fault (LPF), E‐W‐striking western section of the Seertengshan piedmont fault (WSPF), and NW‐striking eastern section of the Seertengshan piedmont fault (ESPF). Based on large‐scale active fault mapping, this article analyzes data from 23 trenches, using an unmanned aerial vehicle to measure the faulted landform, and combines these data with Quaternary dating methods to acquire the paleoearthquake sequences of the LPF, WSPF, and ESPF. Furthermore, this article explores their rupture modes and discusses the structural evolution of two intersection points. Through paleoseismic comparison, seven trenches revealed historical earthquakes from 7 BC, with a common magnitude ofM8.1. The trenches also revealed seven paleoseismic events since the Holocene, which conformed to the periodic model with a period of 1.37 ± 0.11 ka. The elapsed time since the latest event (2.0 ka) has exceeded the earthquake recurrence period; thus, the area is currently at risk of anM7.4–8.0 earthquake. The NE‐striking LPF and E‐W‐striking WSPF are connected by two left‐stepping small fault segments. The E‐W‐striking WSPF and NW‐striking ESPF are connected by a large triangular relay ramp.

Recurrence of earthquakes in the area of the Toktogul HPP cascade

A brief statistical analysis of the current seismicity of the Toktogul region of the Kyrgyz Republic is done. The analysis concerns the region where the Toktogul HPP cascade on the Naryn River is located, and covers the period from 1973 to 2021 years. The space-time distributions of earthquakes, accumulation characteristics, probability and recurrence of seismic events of various magnitudes are considered. According to the analysis results, the maximum magnitude of seismic events in the Toktogul region can be ∼ 7.4, and the recurrence period of earthquakes with a magnitude of M ≥ 7 and above T ≥ 10 years is equal.

Lessons from a Small Local Earthquake (Mw 3.2) That Produced the Highest Acceleration Ever Recorded in Mexico City

AbstractA reliable estimation of seismic hazard-facing Mexico City from local earthquakes has suffered from poor seismic instrumentation, complex crustal structure, large and variable site amplification, and lack of knowledge of recurrence period of earthquakes on the mapped faults. Owing to recent improvement in local seismic networks, an earthquake swarm activity, which occurred in June–August 2019, was well recorded. The largest event of the sequence, an Mw 3.2 earthquake, caused panic in the city and produced peak ground acceleration (PGA) exceeding 0.3g at the closest station (MHVM) about 1 km away. An analysis of the event shows that it had normal-faulting focal mechanism, consistent with northeast–southwest-oriented mapped faults in the region. It was located at a depth of ∼1 km and had a low stress drop (∼0.1 MPa). We find that the high PGA for this low stress-drop event resulted from high-frequency amplification at MHVM (about factor of ∼6 around 13 Hz), likely due to topographic site effects, superimposed on a pervasive broadband amplification of seismic waves at hill-zone sites in the Valley of Mexico (up to ∼10 in the frequency band of 0.2–10 Hz). Simulation of ground motion for a scenario Mw 5.0 earthquake, using an empirical Green’s function technique, reveals that such an event may give rise to significant seismic intensities in the lake-bed zone of Mexico City. The results emphasize the need to re-evaluate the seismic hazard to Mexico City from local crustal earthquakes in the Valley of Mexico.

Geological and geomorphic evidence for activity of the Mengzi fault along the southeastern margin of the Tibetan Plateau

Few studies have been conducted on the activity of the Mengzi fault system, which is located to the southeast of the Sichuan-Yunnan block. The Mengzi fault is distributed along the eastern margin of the Mengzi basin. However, little is known about the location, length, and activity of the fault or the occurrence of paleo-earthquakes during the late Quaternary. This paper studies the geometric distribution and activity of the fault via remote sensing imagery interpretation, fault outcrops in the area, faulted landforms and chronological analyses. The results show that the Mengzi fault extends from Nandong (Kaiyuan basin) in the north through the eastern margin of the Mengzi basin to Pingbian in the southeast, eventually intersecting with the Honghe fault. The Mengzi fault is approximately 250 km long and is characterized as a reverse strike-slip fault. We survey and calculate the offset gullies and terraces dislocated by the fault; combined with sample dating, we calculate the horizontal slip rate of the fault since 30 ka BP to be 0.91–1.56 mm/a. Three paleo-events since 30–40 ka BP are observed with a 10-ka major earthquake recurrence period. We analyze the relationships among the Mengzi fault, southern Xiaojiang fault, and Qujiang-Jianshui fault and note a slip rate loss of ≥8 mm/a from the southern Xiaojiang fault that was absorbed by reverse dextral strike-slip faulting and lateral shortening of the Qujiang-Jianshui fault and the Mengzi fault. The Mengzi fault plays an important role in the adjustment of the large slip rate reduction along the southern Xiaojiang fault. Moreover, the Mengzi fault has a similar tectonic position to the seismogenic faults of the 2008 Wenchuan earthquake, 2013 Lushan earthquake and 2014 Ludian earthquake, and the Mengzi fault and southern Xiaojiang fault both accumulate the energy generated by the southeastward movement of the Sichuan-Yunnan block. Studies on the Mengzi fault are helpful for renewing our understanding of the tectonic patterns of the southeastern Sichuan-Yunnan block and delimiting the boundary of the southeastern block margin. Furthermore, because the cities of Mengzi and Kaiyuan are located along the Mengzi fault, this study has practical significance for earthquake disaster mitigation.

3D seismogenic model of the 2015 Gorkha earthquake and subsequent seismic risk

On April 25th, 2015, the moment magnitude (M-w) 7. 8 Gorkha earthquake, Nepal occurred in Himalaya orogenic belt, which seems insufficient to release the accumulated energy as suggested previously. The following seismic risk assessments are mostly based on the two dimensional or pseudo-three dimensional inversions of tectonic deformation. Here we analyze the relationship between the main shock and biggest aftershock of the 2015 Gorkha earthquake sequence, and its unevenness in time and space. Combining focal mechanism solutions, crustal velocity structure, relocated aftershocks, and inversion results from InSAR, we construct a three dimensional model which changes along both the strike and dip directions of the Main Himalayan Thrust. The finite element method with nonlinear friction is used to calculate the fault behavior and block deformation in one earthquake recurrence period. Comparison between the forward calculation results and the co-seismic deformation observed from InSAR, and co-seismic slip inverted from deformation observations, and time-space evolution of historical earthquakes revealed that the three dimension model is close to the reality. The results suggest two potential seismic risk regions in the future: a big earthquake might be located in the east of the 1934 Bihar-Nepal M-w similar to 8. 1 earthquake, and a moderate to major event might take place to the southeast of the aftershock M(w)7. 3 earthquake.

Control spectra for Quito

Abstract. The Metropolitan District of Quito is located on or very close to segments of reverse blind faults, Puengasí, Ilumbisí–La Bota, Carcelen–El Inca, Bellavista–Catequilla and Tangahuilla, making it one of the most seismically dangerous cities in the world. The city is divided into five areas: south, south-central, central, north-central and north. For each of the urban areas, elastic response spectra are presented in this paper, which are determined by utilizing some of the new models of the Pacific Earthquake Engineering Research Center (PEER) NGA-West2 program. These spectra are calculated considering the maximum magnitude that could be generated by the rupture of each fault segment, and taking into account the soil type that exists at different points of the city according to the Norma Ecuatoriana de la Construcción (2015). Subsequently, the recurrence period of earthquakes of high magnitude in each fault segment is determined from the physical parameters of the fault segments (size of the fault plane and slip rate) and the pattern of recurrence of type Gutenberg–Richter earthquakes with double truncation magnitude (Mmin and Mmax) is used.

Kinematic analysis and palaeoseismology of the Edremit Fault Zone: evidence for past earthquakes in the southern branch of the North Anatolian Fault Zone, Biga Peninsula, NW Turkey

The Edremit Fault Zone (EFZ) forms one of the southern segments of the North Anatolian Fault Zone (NAFZ) at the northern margin of the Edremit Gulf (Biga Peninsula, South Marmara Region, Turkey). Stratigraphic, structural and kinematic results indicate that basinward younging of the fault zone, in terms of a rolling-hinge mechanism, has resulted in at least three discrete Miocene to Holocene deformational phases: the oldest one (Phase 1) directly related to the inactive Kazdağ Detachment Fault, which was formed under N–S trending pure extension; Phase 2 is characterised by a strike-slip stress condition, probably related to the progression of the NAFZ towards the Edremit area in the Plio–Quaternary; and Phase 3 is represented by the high-angle normal faulting, which is directly interrelated with the last movement of the EFZ. Our palaeoseismic studies on the EFZ revealed the occurrence of three past surface rupture events; the first one occurred before 13178 BC, a penultimate event that may correspond to either the 160 AD or 253 AD historical earthquakes, and the youngest one can be associated with the 6 October 1944 earthquake (Mw = 6.8). These palaeoseismic data indicate that there is no systematic earthquake recurrence period on the EFZ.

Seismites in the Pleistocene succession and recurrence period of large earthquakes in the Kathmandu Valley, Nepal

Kathmandu Valley, which is a rapidly growing place in Nepal, was largely damaged by the earthquakes of April 25 (Mw 7.8) and May 12 (Mw 7.3). For taking measures against future large earthquakes, knowledge of the long-term earthquake history is crucial for future disaster prevention or disaster reduction. Twelve seismites thicker than 0.2 m were identified from the Tokha Formation, the major part of which was deposited at about 20 – 17 ka (calibrated 14C ages). Some seismites show evidence of sliding occurred on the delta plain. The reconstructed earthquake recurrence period is ca. 0.25 ka or shorter. Six of the seismites show evidence of sliding when deformation structures were formed. This was probably due to the tilting of the surface in the studied site, where a buried flexure was discovered nearby. The discovery of the seismites with sliding in the delta plain deposit suggests the possibility of sliding by future large earthquakes and requirement of risk management for the plain area of the Kathmandu Valley.

Seismicity and seismotectonics of the Red Sea Region

The historical seismicity of the Red Sea region between latitudes 13 and 30° N and longitudes 32 and 46° E has been revised. It is found that during the last 1400 years, some 88 historical earthquakes have occurred with magnitudes M ≥ 5.6. Only two M = 7.0 are reported, one in each of the northern and southern Red Sea regions, followed by two and one 6.8 in the northern and southern regions, respectively. During the period 1960–2010, some 1310 instrumental earthquakes have occurred in the region with M ≥ 4.0. The largest (M = 7.1) occurred in the Gulf of Aqaba, followed by a 6.9 in the entrance of the Gulf of Suez, followed by a 6.7 and a 6.4 that occurred in the southern Red Sea region. All others had M ≤ 6.2. More than 90 % of the seismicity has occurred in the form of sequences and swarms and are believed to be volcanic related. Thus, the seismic hazard of the study region remains quite limited. Both northern and southern parts of the Red Sea region are of comparable seismic activities, while that of the central part is of lower activity. The historical and instrumental seismicity data show excellent correlation with the general tectonics of the study region. These also show that earthquake activity has fluctuated with time from one region to the other. In the Red Sea proper, more than 83 % of the seismic moment is associated with the regional faults of the axial trough with noticeable concentration of activity where the NE trending strike-slip faults cross this trough. Published fault plane solutions for the largest instrumental earthquakes of the last few decades show that both normal and strike-slip faults are active in support of a divergent environment between the Arabian and African plates. Shallow seismicity is a characteristic feature of this region. The data indicates that lithospheric deformations beneath the gulfs area are restricted to the upper part of the crust, while beneath the Red Sea south of latitude 27.8°, these appear to concentrate partially within the crust down to 10 km depth and much more within the uppermost mantle, mostly from 20.1 to 40 km depths. Very little earthquakes occur at depths deeper than 60 km. Frequency-magnitude results of both historic and instrumental data gave the expected b value close to 1.0. The calculated recurrence periods for earthquakes with M = 6, 6.5 and 7 are 30 ± 2 years, 150 ± 10 years and 600 ± 20 years, respectively. The data show that the threshold magnitude for the study region is 4.0, and slightly more for the axial trough.

Decomposition and Evolution of Intracontinental Strike‐Slip Faults in Eastern Tibetan Plateau

Abstract:Little attention had been paid to the intracontinental strike‐slip faults of the Tibetan Plateau. Since the discovery of the Longriba fault using re‐measured GPS data in 2003, an increasing amount of attention has been paid to this neglected fault. The local relief and transverse swath profile show that the Longriba fault is the boundary line that separates the high and flat tomography of the Tibet plateau from the high and precipitous tomography of Orogen. In addition, GPS data shows that the Longriba fault is the boundary line where the migratory direction of the Bayan Har block changed from eastward to southeastward. The GPS data shows that the Longriba fault is the boundary fault of the sub‐blocks of the eastern Bayan Har block We built three‐dimensional models containing the Longriba fault and the middle segment of the Longmenshan fault, across the Bayan Har block and the Sichuan Basin. A nonlinear finite element method was used to simulate the fault behavior and the block deformation of the Eastern Tibetan Plateau. The results show that the low resistivity and low velocity layer acts as a detachment layer, which causes the overlying blocks to move southeastward. The detachment layer also controls the vertical and horizontal deformation of the rigid Bayan Har block and leads to accumulation strain on the edge of the layer where the Longmenshan thrust is located. After a sufficient amount of strain has been accumulated on the Longmenshan fault, a large earthquake occurs, such as the 2008 Wenchuan earthquake. The strike slip activity of the Longriba fault, which is above the low resistivity and low velocity layer, partitions the lateral displacements of the Bayan Har block and adjusts the direction of motion of the Bayan Har block, from the eastward moving Ahba sub‐block in the west to southeastward moving Longmenshan sub‐block in the east. Four models with different depths to the Longriba fault were constructed: (1) a shallow fault with a depth of only 4 km, (2) a deeper fault that is half as deep as the Longmenshan fault, (3) a deep fault that is 2 km shallower than the low resistivity and low velocity layer, and (4) a fault that is as deep as the low resistivity and low velocity layer. The activity and influence of the Longriba fault with different development stage under this tectonic system were shown: in one Earthquake recurrence period, the rupture region of the fault increases with the depth of the fault, and the lateral slip partition by the fault also changes with the fault depth. It suggests that the Longriba fault is a newly generated fault that developed after the quick uplift in Late Cenozoic along this tectonic setting and gradually extended from the northwest to southeast. The calculations provide the characteristic of block deformation and fault behaviors of intra‐continental strike‐slip fault and major boundary thrust faults in the eastern margin of the Tibet plateau. Although the low resistivity and low velocity layer controls the deformation of the Bayan Har block and the uplift of the Longmenshan thrust, the partition of the Longriba fault has an important influence on the intra‐plate deformation and modern geomorphic evolution.

Employing Cantor sets for earthquake time series analysis in two zones of western Turkey

In this study, a fractal approach is employed to analyze the seismic history of Fethiye and Simav zones in the West of Turkey. In this scope, a database, including the set of earthquakes in two seismogenic zones, is compiled. Applying fractal dimension and probability concepts, it is aimed to find out the occurrence probability of earthquakes having magnitudes equal to or greater than a threshold level. The results are analyzed in detail and relationships among the fractal dimension, threshold magnitude, probability intercept, and critical time scale are presented. The analyses revealed that activities in the Fethiye Zone are more frequent and continuous than those in the Simav Zone. As mentioned in previous studies, the critical time scales at certain magnitude thresholds can be referred to as the lower limit of the recurrence period of earthquakes in these zones.

The hazard potential of the western segment of the Makran subduction zone, northern Arabian Sea

Evaluating the hazard potential of the Makran subduction zone requires understanding the previous records of the large earthquakes and tsunamis. We address this problem by searching for earthquake and tectonic proxies along the Makran Coast and linking those observations with the available constraints on historical seismicity and the tell-tale characteristics of sea floor morphology. The earthquake of Mw 8.1 of 1945 and the consequent tsunami that originated on the eastern part of the Makran are the only historically known hazardous events in this region. The seismic status of the western part of the subduction zone outside the rupture area of the 1945 earthquake remains an enigma. The near-shore shallow stratigraphy of the central part of Makran near Chabahar shows evidence of seismically induced liquefaction that we attribute to the distant effects of the 1945 earthquake. The coastal sites further westward around Jask are remarkable for the absence of liquefaction features, at least at the shallow level. Although a negative evidence, this possibly implies that the western part of Makran Coast region may not have been impacted by near-field large earthquakes in the recent past—a fact also supported by the analysis of historical data. On the other hand, the elevated marine terraces on the western Makran and their uplift rates are indicative of comparable degree of long-term tectonic activity, at least around Chabahar. The offshore data suggest occurrences of recently active submarine slumps on the eastern part of the Makran, reflective of shaking events, owing to the great 1945 earthquake. The ocean floor morphologic features on the western segment, on the contrary, are much subdued and the prograding delta lobes on the shelf edge also remain intact. The coast on the western Makran, in general, shows indications of progradation and uplift. The various lines of evidence thus suggest that although the western segment is potentially seismogenic, large earthquakes have not occurred there in the recent past, at least during the last 600 years. The recurrence period of earthquakes may range up to 1,000 years or more, an assessment based on the age of the youngest dated coastal ridge. The long elapsed time points to the fact that the western segment may have accumulated sufficient slip to produce a major earthquake.

The Effect of Two Fault Segments Sliding Velocity on Strong Earthquakes

For researching the strong earthquake recurrence period of Kusai Lake and Xidatan fault segment in different sliding velocities, we apply the spring-block model (or BK model) controlled by the velocity and state depended frictional constitutive. Through numerically solving the one order differential equations picturing the block (or fault segment) motion, the parameter charactering the fault segment motion is achieved. Finally, we find the recurrence period of strong earthquake is shorter in fast sliding velocity than that in slow one. The 0.1 mm changing of fault segment sliding velocity per year will make the several hundreds years of variation in strong earthquake recurrence period.

A Developing Plate Boundary: Tianshan-Baikal Active Tectonic Belt

It is obvious that a great amount of strong earthquakes in central Asia occurred densely along Tianshan-Baikal belt; however, none of huge continuous fault has been revealed on the surface along the belt. It caused academic argument related to their relationship. The authors analyzed its seismic activity in terms of seismicity in time-space domain, zoning feature, stress field, and recurrence period of earthquakes. In addition, we studied the Bouguer gravity and isostatic anomaly, and calculated the distribution of density and shear wave velocity in the upper mantle. It is found that there is a gradient belt of density and velocity along NE direction at the depths of 70–250 km, which is actually a Cenozoic boundary of cold mantle and hot mantle, and has an overpass relation with the structure existing in the upper lithosphere. It is inferred that this gradient belt in the upper mantle played an important role in controlling present tectonic movement and stress field in Eurasia continent. As far as the earthquake nature in this belt is concerned, it is neither an interplate earthquake nor an intraplate one in the traditional sense. Such kind of earthquake caused by overpass structure actually belongs to the structural earthquake, and is of interplate within a continent. In this paper, the overpass relation and mirror relation in time-space domain between deep and shallow structures are discussed briefly. It is also noted that the overpass structures shown in the areas of both north-south seismic belt of China and eastern seismic belt of Iran are related to a special structure in the upper mantle. We conclude that the Tianshan-Baikal active tectonic belt is a developing boundary of plates, a typical tectonic within a continent, which separates Eurasian plate into two parts, i.e., the stable Russian-Siberia subplate to the north and the active China-Southeast Asia subplate to the south.

Experimental Study of the Earthquake Recurrence Period and the Trend of Post-seismic Development

In order to study the earthquake recurrence and the characteristics of earthquake series, rupture tests of rock samples and plexiglass samples were made. On rock samples, a number of acoustic emission (AE) and strain measuring points were deployed; the load was one side direct shear. The variation characteristics of AE and strain at different detecting points around the extra large fracture were observed and studied. On plexiglass samples, a series of inclined cracks were prefabricated by a small-scale compressive testing machine. The samples were then loaded on a shockproof platen, when the samples were loaded, the stress intensity factor (SIF) was determined by the laser interferometric technique and shadow optical method of caustics. The fracture conditions such as material toughness around the extra large fracture were also studied. From those experimental results and the theory of fracture mechanics, the earthquake recurrence period and the trend of post-seismic development were studied.

Tectonic stress field and large earthquake recurrence period in China

Tectonic stress field and large earthquake recurrence period in China

Kinematic features of the seismogenic fault of the Tangshan earthquake and the recurrence period of large earthquakes

By the inversion method of uneven slippage of faults in the depths (Liu et al., 1995) and using the crustal deformation data of six phases, the movement states of seismic fault of the Tangshan earthquake in five time periods before, during and after that earthquake are computed. The result of computation has revealed the movement process of seismic fault, during which the fault moved at an increasing rate before the quake, slipped suddenly during the quake, and became relaxed, adjusted and stabilized gradually after the quake. Moreover, the recurrence period of earthquakes in Tangshan is computed using the relation that the slippage of seismic fault bears with strain energy.