Recurrence Interval Of Earthquakes Research Articles

Introducing stochastic recurrence interval to classification algorithms for identifying asperity patterns

The introduction of stochastic earthquake recurrence times in feature vector is attempted for the identification of asperities in the area of Hokkaido, Japan, using machine learning algorithms. Seismicity attributes, feature selection algorithms, and class balancing techniques were used. The stochastic attributes of earthquake density in space, b-value, and the earthquake recurrence intervals were set as asperity identifiers. The study area was divided into 422 subareas, and in each one of them the aforementioned attributes were estimated for each subarea. For increasing the method efficiency a feature selection algorithm was utilized to indicate which of the selected attributes have the potential to contribute to the identification of asperities. A feature vector is presented, combining the attributes mentioned above, and well-known machine learning algorithms were used to identify the asperities locations. The performance of the method was tested with the 10-fold cross-validation technique and was found sufficient in means of F1 score.

Microatolls document the 1762 and prior earthquakes along the southeast coast of Bangladesh

In order to understand the seismic hazard associated with the Sunda megathrust along SE Bangladesh, it is necessary to document geologic evidence for the 1762 Arakan earthquake (M8.5–8.8) and prior events. Historical records indicated that the 1762 earthquake caused extensive damage along the Arakan segment of the Sunda subduction system, but geologic evidence for the earthquake farther north is necessary to better understand its associated seismic hazard to the heavily populated nation of Bangladesh. To document the paleoseismic history and understand ongoing tectonic deformation, we conducted detailed analyses of corals and microatolls in Saint Martin's Island, SE Bangladesh. The coral growth bands were studied, dated using U/Th systematics and their elevation was measured using high-precision GPS with RTX™ capability. The U/Th dating and >2 m of elevation differences between dead and living corals provide strong evidence of the coseismic uplift of 1762 Arakan earthquake. Based on annual banding patterns and reconstruction of the highest level of survival, coral microatolls indicate a tectonic subsidence rate of 2.2 ± 0.8 mm/yr prior to their uplift, consistent with elastic strain accumulation before the earthquake. In contrast, annual growth bands of a living coral microatoll indicate that Saint Martin's Island is presently experiencing uplift, at a rate of 1.8 ± 0.1 mm/yr. This suggests that the anticline underlying Saint Martin's Island is actively deforming following the earthquake. Our study also provides evidence for two additional earthquakes taking place in ~700 and ~1140 CE. These findings suggest a preliminary earthquake recurrence interval of ~500 years. Based on our results, the 1762 rupture can be extended from Faul Island (18°N) to Saint Martin's Island in SE Bangladesh (20.6°N). The motions documented from the corals suggest that this segment of the Arakan collision zone is storing sufficient energy to cause a future earthquake of M > 8.

Effect of large-scale surface water level fluctuations on earthquake recurrence interval under strike-slip faulting

While tectonic motion is seen as a primary cause of the earthquakes, the effects of water level fluctuations on geological rates of seismicity have not been studied in depth. Can fluctuations of tens to hundreds of meters significantly perturb local fault systems and modify the behaviour of their seismic cycles? Our novel theoretical modelling can explain variability in the paleoseismic rates of large earthquakes rupturing strike-slip faults, by large-scale water level fluctuations in basins overlying the faults. We demonstrate that water level increase can significantly affect effective stresses at the faults, generate immediate and delayed seismic responses, and accelerate seismic events under strike-slip faulting regime. Both, water level induced stress change and hence seismic recurrence interval, are significantly affected by an interplay between hydro-mechanical properties of the fault zone. Our modelling demonstrates that water level fluctuation of historic water bodies in the tectonic depression of the Dead Sea fault could have triggered changes in the paleo-seismic rates.

Constraining Central Washington’s Potential Seismic Hazard

Fault geometry and slip rate analyses show deformation in the Yakima Fold Province accelerated in the Pleistocene and has remained elevated, offering new insights into earthquake recurrence intervals.

A Statistical Model for Earthquake Recurrence Based on the Assimilation of Paleoseismicity, Historic Seismicity, and Instrumental Seismicity

AbstractPaleoearthquakes and historic earthquakes are the most important source of information for the estimation of long‐term earthquake recurrence intervals in fault zones, because corresponding sequences cover more than one seismic cycle. However, these events are often rare, dating uncertainties are enormous, and missing or misinterpreted events lead to additional problems. In the present study, I assume that the time to the next major earthquake depends on the rate of small and intermediate events between the large ones in terms of a “clock change” model. Mathematically, this leads to a Brownian passage time distribution for recurrence intervals. I take advantage of an earlier finding that under certain assumptions the aperiodicity of this distribution can be related to the Gutenberg‐Richter b value, which can be estimated easily from instrumental seismicity in the region under consideration. In this way, both parameters of the Brownian passage time distribution can be attributed with accessible seismological quantities. This allows to reduce the uncertainties in the estimation of the mean recurrence interval, especially for short paleoearthquake sequences and high dating errors. Using a Bayesian framework for parameter estimation results in a statistical model for earthquake recurrence intervals that assimilates in a simple way paleoearthquake sequences and instrumental data. I present illustrative case studies from Southern California and compare the method with the commonly used approach of exponentially distributed recurrence times based on a stationary Poisson process.

Temporal slip-rate stability and variations on the Hope Fault, New Zealand, during the late Quaternary

The Hope Fault transfers slip from Hikurangi subduction to the Alpine Fault in the northern South Island of New Zealand. It accommodates mainly dextral strike slip and currently carries the highest slip rate in the Marlborough Fault System. Displacements, displacement rates and earthquake recurrence intervals have been determined using a combination of high resolution LiDAR for 59 dextral displacements (~2.5–200 m) together with calibrated radiocarbon ages (~130 yr to 13,000 yr) for abandoned stream channels, terrace risers and alluvial fans. Mean single-event displacement (SED) of 3 ± 0.6 m (2.2 to 4.6 m for 21 measurements) and mean recurrence interval of ~266 ± 100 yr (range 128 to 560 yr) have been determined for the five most recent surface-rupturing earthquakes. On time scales ≥2300 yr the dextral slip rate is uniform at 12.2 ± 2.4 mm/yr, however, when averaged over time intervals of ~230 to 1700 yr slip rates range from ~4 to 46.4 mm/yr. This order-of-magnitude variability in slip rate over shorter timescales cannot be fully attributed to errors in displacement and age data, and is at least partly due to variations in earthquake recurrence interval and inferred SED. Short-term non-characteristic earthquake behaviour may be due to changes in fault loading arising from stress interactions between different segments of the Hope Fault and nearby faults.

Active faulting in the central Betic Cordillera (Spain): Palaeoseismological constraint of the surface-rupturing history of the Baza Fault (Central Betic Cordillera, Iberian Peninsula)

This paper on the Baza Fault provides the first palaeoseismic data from trenches in the central sector of the Betic Cordillera (S Spain), one of the most tectonically active areas of the Iberian Peninsula.With the palaeoseismological data we constructed time-stratigraphic OxCal models that yield probability density functions (PDFs) of individual palaeoseismic event timing. We analysed PDF overlap to quantitatively correlate the walls and site events into a single earthquake chronology. We assembled a surface-rupturing history of the Baza Fault for the last ca. 45,000 years. We postulated six alternative surface rupturing histories including 8–9 fault-wide earthquakes. We calculated fault-wide earthquake recurrence intervals using Monte Carlo. This analysis yielded a 4750–5150 yr recurrence interval. Finally, compared our results with the results from empirical relationships.Our results will provide a basis for future analyses of more of other active normal faults in this region. Moreover, our results will be essential for improving earthquake-probability assessments in Spain, where palaeoseismic data are scarce.

The Problems of Seismic Risk Prediction for the Territory of the Lower Amur Region: Paleoseismogeological and Seismological Analysis

The studied region is located at the junction between the Pacific and Central Asian seismoactive belts. Macroseismic data on earthquakes of this region are available for the last 150 years, while instrumental seismological observations began in the mid-20th century; however, the recurrence interval of strong earthquakes can be up to several centuries and even thousands of years. In this respect, many areas of the Amur region had been believed to be nearly aseismic until earthquakes occurred there. Paleoseismogeological studies of recent years have allowed the character of Holocene displacements to be estimated for some of the main regional structures. As a result, the main tendencies of the Late Quaternary geological evolution of the region remain uncertain and the potential seismogenerating structures are not completely known. Therefore the problem of revealing new zones and periods of seismic activity is topical for the entire Amur region. The importance of this problem is related to the weak degree of study of the region by contemporary methods of active tectonics, the intensive development of engineering infrastructure, which is vulnerable to seismic impacts, and the necessity of long-term seismic forecasting. The present work provides the results of paleoseismogeological studies of the active faults in the Amur region. On the basis of new data on the magnitude potential of seismogenerating structures based on the magnitudes of historical earthquakes and instrumentally recorded ones, we have estimated the seismic effects from strong deep-focus earthquakes and the attenuation coefficients and calculated radii of the first three isoseismals for crustal earthquakes. By using the methods of statistical modeling, we distinguish the periods when seismic effects increased from earthquakes with 2 ≤ M ≤ 6. It is shown that seismic hazard assessment should take into account the dynamics of the seismic regime, caused by the change of the earthquake source depth. It is found that the epicenters of earthquakes with 5 ≤ M ≤ 6 form non-crossing seismic zones in different phases of changes in the Earth’s annual rotation.

U/Th Dating of the Akhüyük Fissure Ridge Travertines in Ereğli, Konya (Central Anatolia, Turkey): Their Relationship to Active Tectonics

Fissure ridge travertines that form the Akhuyuk travertine mass are located in Central Anatolia and are exposed in an area of 1.5 km $$^{2}$$ with N30 $$^{\circ }$$ W direction. These fissure ridge travertines have ages determined between 3345 ± 105 yr and 47850 ± 980 yr by U-series dating methods. Development of the travertines can be correlated with faults that have been active since the late Pleistocene. The dilation rate in the Eregli (Konya) basin was determined using age data and the widths of the banded travertines at the opening center of the fissure ridge travertines. The dilation rate for the formation of Akhuyuk travertines yields 0.025–0.05 mm yr $$^{-1}$$ on average. When considering positions and extension directions of fissure ridge travertines, they are consistent with the Tuz Golu Fault Zone which is one of the most important structures in the region. The maximum earthquake intensity potential in this region is estimated to be $$M_\mathrm{s}$$ 6.3, when the dilation rate of the fissure ridge travertines is taken to be 0.05 mm yr $$^{-1}$$ and with a 10,000-year earthquake recurrence interval.

Recurrence interval of strong earthquakes in the se Altai, Russia revealed by tree-ring analysis and radiocarbon dating

Abstract This paper presents the results of paleoseismogeological investigations including tree-ring analysis and radiocarbon dating in pleistoseist zone of the 2003 Chuya earthquake, SE Altai, Russia. Twenty-five radiocarbon dates of previously unknown evidences of prehistoric earthquakes along the fault bounders of the Chagan-Uzun massif, North Chuya and South Chuya ranges are reported. Perspectives of applying dendroseismological approach within the high mountainous seismically active southeastern part of Russian Altai are demonstrated. In addition to estimating the germination ages of trees growing on the bare surfaces of seismically triggered landslides, analysis of wood penetrating injuries in the individual tree ring series was applied for dating paleorock-falls. Analysis of distribution patterns of tree-ring anomalies and injured trees suggests a criterion of recognizing seismic origin of past rock-falls. Dendrochronologically obtained dates of abrupt intensifications of rock-falls can be considered as supposed dates of past earthquakes, which should be verified by alternative proxy data. Obtained results argue for the high regional seismicity in the second half of the Holocene. Strong earthquakes occurred here AD 1532, and 600–700, 1300–1500, 2400–2700, 3400–3700, 3800–4200 cal BP. This data clarifies the chronology of seismic events within the SE Altai. The specified recurrence interval of strong earthquakes is about 400 years during the last 4000 years.

Mid- to late-Holocene marine inundations inferred from coastal deposits facing the Nankai Trough in Nankoku, Kochi Prefecture, southern Japan

This study investigates the Holocene sedimentary history of a small coastal lowland in Nankoku, Kochi Prefecture, on the coast of southern Japan facing the Nankai Trough. The sedimentary fill of the lowland area consists mainly of marine-brackish clay overlain by beds of freshwater clay and peat. We found four laterally extensive sand sheets, one directly underlying the freshwater deposits and the other three interbedded with them. Radiocarbon dates show that these sand sheets were deposited between 5970 and 2440 cal. BP. Although the sand sheets contained few marine-brackish diatoms, they were concentrated in the seaward part of the study site, suggesting that they were deposited by marine inundations. These sand sheets were formed as a result of tsunamis or unusually large storm surges. The apparent frequency of marine inundations during 5970–2440 cal. BP was much lower than that of megathrust earthquakes along the Nankai Trough recorded during the last 1300 years. Event deposits were absent between 2440 and 960 cal. BP, a gap that we attribute to the development of beach ridges. The new marine inundation records reported here will aid efforts to reconstruct the timing and recurrence intervals of megathrust earthquakes in the western Nankai Trough.

Seismic risk assessment and design of tourism buildings using probability analysis

The average recurrence interval of major earthquakes is approximately a century. Consequently, the existing data are insufficient for an accurate estimation of average losses. The main objective of this research is to study the disaster-prone characteristics of hotels by using modern concepts of risk management (i.e., loss exceedance probability analysis, seismic hazard analysis and so on) and then combine the relevant basic research data from domestic and foreign sources to develop a seismic risk assessment and management system suitable for the hospitality industry. The proposed seismic risk management and risk evaluation system will also provide governments, hotel asset owners, insurance companies and banks in Taiwan that have similar regional characteristics with the necessary seismic risk information to help the tourism industry effectively evaluate and manage the natural disaster risk.

Seismic risk assessment and design of tourism buildings using probability analysis

The average recurrence interval of major earthquakes is approximately a century. Consequently, the existing data are insufficient for an accurate estimation of average losses. The main objective of this research is to study the disaster-prone characteristics of hotels by using modern concepts of risk management (i.e., loss exceedance probability analysis, seismic hazard analysis and so on) and then combine the relevant basic research data from domestic and foreign sources to develop a seismic risk assessment and management system suitable for the hospitality industry. The proposed seismic risk management and risk evaluation system will also provide governments, hotel asset owners, insurance companies and banks in Taiwan that have similar regional characteristics with the necessary seismic risk information to help the tourism industry effectively evaluate and manage the natural disaster risk.

Seismic hazard assessment of Koyna region, Peninsular India: using geospatial approach

BackgroundEarthquake-prone regions from the stable continental regions (like Peninsular India) warrant total seismic hazard estimation from possible sources — reservoir induced or tectonic. The Koyna region falls in the so-called stable continental region, though previously considered as aseismic because of its location in the Peninsular India, which was argued to be the continental Shield region; however, it is seismically active ever since the December 10, 1967, strong earthquake (M6.5) which killed around 200 people and damaged properties. The event was initially attributed to reservoir-induced seismicity. The present study aims at mapping the spatial distribution of hazard intensity in terms of peak ground acceleration and damage potential expressed as Modified Mercalli Intensity (MMI) levels owing to the scenario earthquakes (M4.0 to M6.9) from the linear sources and background seismicity in the Koyna region. For the seismic source model, geospatial integration approach is used. To delineate the source boundaries we perform spatial analysis of seismicity attributes and assigning weights based on the geological information. In addition, spatial buffering of thematic layers of faults and lineaments is applied to truncate the spatial uncertainties. Thematic attribute layers are integrated over the SRTM-DEM-derived geomorphic features and spatial seismicity pattern to define the possible linear seismic source zones. We employ ArcGIS® to perform geospatial analysis and to integrate thematic spatial information finally to prepare the seismic hazard and damage potential zones for the Koyna region.ResultsWe present the probabilistically estimated seismic hazard and damage potential estimates for the Koyna region. Spatial mapping of the hazard parameters is performed on Geographic Information System (GIS) platform. Along with the historical and instrumental earthquake data, we incorporate updated and relocated seismic events from circa 1618 to 2017 covering ~ 400 years period, for analyzing the mean annual rates of seismicity and earthquake recurrence intervals. The anticipated recurrence intervals of earthquakes ~ M5.5 is around 100 ± 10 years. The estimated peak ground acceleration (PGA) for 10% probability being exceeded in 50 years (i.e. 500 years of return period) is greater than 21% g is anticipated for the area located (~30 km radius) between the Koyna and Warna Reservoirs.ConclusionsThe hazard estimates for the 500 years return period earthquake scenarios (M4.0 to M6.9) are based on the bedrock level estimation. Estimated PGA-values are grouped into three categories that are relatively defined as high, moderate, and low hazard zones, respectively. Slightly damaging intensity (MMI-VII level) expected in 50 years has ~ 40% probability and PGA greater than 21% g for the area which is located between Koyna and Warna Reservoirs, which is identified as high hazard zone.

Late Holocene slip rate and average recurrence interval of great earthquakes on the Shangzhi segment of the Yilan‐Yitong Fault Zone, northeastern China: Constraints from paleo‐earthquakes and historical written records

AbstractThe Yilan‐Yitong Fault Zone (YYFZ) is considered to be the key branch of the Tancheng‐Lujiang Fault Zone (TLFZ) in northeastern China. Although the Mesozoic and early Cenozoic deformation of the YYFZ has been studied intensively over the past century, few estimates of slip rate and recurrence interval of large earthquakes in the late Quaternary, which are the two most important parameters for understanding the potential seismic hazard of this crucial structure, were obtained. Based on integrated interpretations of high resolution satellite images and detailed geologic and geomorphic mapping, linear landforms were identified, including fault scarps and troughs, along the Shangzhi segment of the YYFZ, which exceeds 25 km in length. Synthesized results of trench excavations and differential GPS measurements of terrace surfaces indicate that two events (E1, E2) occurred along the Shangzhi segment during the late Holocene, which resulted in 3.2 ±0.1 m of total vertical co‐seismic displacement with clear features of thrust motion. 14C dating of samples suggests that event E1 occurred between 440 ±30 years BP and 180 ±30 years BP and that event E2 occurred between 4 090 ±30 years BP and 3 880 ±30 years BP, which indicates that the minimum vertical slip rate of the Shangzhi segment of the YYFZ has been approximately 0.8 ±0.03 mm/year during the late Holocene. Constraints from paleo events and the slip rate suggest that the average recurrence interval of major earthquakes on the YYFZ is 3 800 ±200 years. Historical documents in Korea show that event E1 possibly corresponds to the earthquake that occurred in AD 1810 (the Qing Dynasty in Chinese history) in the Ningguta area, which had surface‐wave magnitude (Ms) of 6.8–7.5. Studies of kinematics show that the right‐lateral strike‐slip with a reverse component has been dominant along the YYFZ during the late Holocene.

Earthquake cycle simulations with rate-and-state friction and power-law viscoelasticity

We simulate earthquake cycles with rate-and-state fault friction and off-fault power-law viscoelasticity for the classic 2D antiplane shear problem of a vertical, strike-slip plate boundary fault. We investigate the interaction between fault slip and bulk viscous flow with experimentally-based flow laws for quartz-diorite and olivine for the crust and mantle, respectively. Simulations using three linear geotherms (dT/dz=20, 25, and 30K/km) produce different deformation styles at depth, ranging from significant interseismic fault creep to purely bulk viscous flow. However, they have almost identical earthquake recurrence interval, nucleation depth, and down-dip coseismic slip limit. Despite these similarities, variations in the predicted surface deformation might permit discrimination of the deformation mechanism using geodetic observations. Additionally, in the 25 and 30K/km simulations, the crust drags the mantle; the 20K/km simulation also predicts this, except within 10km of the fault where the reverse occurs. However, basal tractions play a minor role in the overall force balance of the lithosphere, at least for the flow laws used in our study. Therefore, the depth-integrated stress on the fault is balanced primarily by shear stress on vertical, fault-parallel planes. Because strain rates are higher directly below the fault than far from it, stresses are also higher. Thus, the upper crust far from the fault bears a substantial part of the tectonic load, resulting in unrealistically high stresses. In the real Earth, this might lead to distributed plastic deformation or formation of subparallel faults. Alternatively, fault pore pressures in excess of hydrostatic and/or weakening mechanisms such as grain size reduction and thermo-mechanical coupling could lower the strength of the ductile fault root in the lower crust and, concomitantly, off-fault upper crustal stresses.

Late Quaternary paleoseismicity and seismic potential of the Yilan-Yitong Fault Zone in NE China

The Yilan-Yitong Fault Zone (YYFZ), which is composed of two nearly parallel branches with a spacing of 5–30 km and a length of ∼1100 km, is considered to be the key branch of the Tancheng-Lujiang Fault Zone (TLFZ) in NE China. It was traditionally believed that the YYFZ experienced weak activity or was inactive during the Late Quaternary, without the capability to generate strong earthquakes (M ≥ 7), based on the absence of typical outcrops and large historical or instrumental earthquakes (M > 6). However, our paleoseismic study shows that the YYFZ is the primary seismotectonic structure (M ≥ 7) that poses significant earthquake threats to NE China. The synthesis of data collected from geologic investigations, geomorphic mapping, trench logging and the dating of samples indicates that the YYFZ is an active structure that has undergone segmented strong tectonic deformation since the Late Quaternary with a characteristic assemblage of landforms, including linear scarps and troughs, offset or deflected streams, linear sag ponds, small horsts and grabens. The latest ruptures of the YYFZ migrated from previous boundary faults into the basin interior, forming a left-stepping en echelon pattern in plain view, and the kinematics of these events in the Late Quaternary were dominated by reverse dextral slipping. Multi-segment cluster faulting might have occurred during three cluster periods, i.e., ∼34750–35812 a BP, ∼21700–22640 a BP, and ∼4000 a BP-present, which implies that the recurrence interval of large earthquakes along the YYFZ may be as long as tens of thousands of years.

Millennium Recurrence Interval of Morphogenic Earthquakes on the Seismogenic Fault Zone That Triggered the 2016 Mw 7.1 Kumamoto Earthquake, Southwest Japan

Millennium Recurrence Interval of Morphogenic Earthquakes on the Seismogenic Fault Zone That Triggered the 2016 Mw 7.1 Kumamoto Earthquake, Southwest Japan

Silica precipitation potentially controls earthquake recurrence in seismogenic zones

Silica precipitation is assumed to play a significant role in post-earthquake recovery of the mechanical and hydrological properties of seismogenic zones. However, the relationship between the widespread quartz veins around seismogenic zones and earthquake recurrence is poorly understood. Here we propose a novel model of quartz vein formation associated with fluid advection from host rocks and silica precipitation in a crack, in order to quantify the timescale of crack sealing. When applied to sets of extensional quartz veins around the Nobeoka Thrust of SW Japan, an ancient seismogenic splay fault, our model indicates that a fluid pressure drop of 10–25 MPa facilitates the formation of typical extensional quartz veins over a period of 6.6 × 100–5.6 × 101 years, and that 89%–100% of porosity is recovered within ~3 × 102 years. The former and latter sealing timescales correspond to the extensional stress period (~3 × 101 years) and the recurrence interval of megaearthquakes in the Nankai Trough (~3 × 102 years), respectively. We therefore suggest that silica precipitation in the accretionary wedge controls the recurrence interval of large earthquakes in subduction zones.

Paleoearthquakes on the Anninghe and Zemuhe fault along the southeastern margin of the Tibetan Plateau and implications for fault rupture behavior at fault bends on strike-slip faults

Fault bends can serve as fault segment boundaries and are used in seismic hazard assessment. Recent studies addressing whether rupture propagation would be arrested at such structural complexities have commonly focused on computational modeling. However, multi-cycle paleoseismic rupture observations through fault bends have seldom been reported. In this study, we used trenching and radiocarbon dating to reveal paleoseismic rupture histories on the southern segment of the Anninghe fault (ANHF) along the southeastern margin of the Tibetan Plateau to explore multi-cycle surface rupture behavior at an extensional fault bend (with an angle of about 30°) at Xichang between the ANHF and Zemuhe fault (ZMHF). Specifically, nine trenches were opened in a fault depression at Maoheshan site and five paleoseismic events were identified. These have been named E1 through E5 respectively corresponding to events at 1400–935BCE, 420–875CE, 830–1360CE, 1295–1715CE, and 1790CE–Present. After comparison with the historical records of earthquakes around Xichang and previous paleoseismic results, we suggest that the five seismic events are constrained at: 1365BCE–935BCE, 814CE, 950CE- 1145CE, 1536CE and 1850CE, respectively. The average recurrence interval of earthquakes along the southern segment of the ANHF is about 700–800yr. Furthermore, the evidence indicates that surface-faulting events along the southern segment of the ANHF appear to be unevenly spaced in time. Moreover, based on comparisons of seismic events along the ANHF and ZMHF, we find that two fault segments simultaneous ruptured during the 814CE and 1850CE earthquakes, event E3 and the 1536CE earthquake ruptured the ANHF but not rupture the ZMHF. We suggest that the Xichang fault bend is not a persistent fault boundary, indicating that extensional fault bends with an angle of about 30° may not effectively terminate seismic ruptures on strike-slip faults.