Xueze Wen - Academia.edu (original) (raw)
Papers by Xueze Wen
Earthquake prediction practice and a large number of earthquake cases show that there may be abno... more Earthquake prediction practice and a large number of earthquake cases show that there may be abnormal images of small earthquake belts near the epicenter before strong earthquakes occur. For a static small earthquakes spatial distribution, due to the complexity of exhaustive algorithm, the fast automatic identification method of seismic belts has not yet been realized. Visual identification is still the main method of seismic belt discrimination. Based on the Delaunay triangulation, this paper presents a fast automatic identification method of seismic belts. The effectiveness of this method is proved by a 1000 random points test and an actual example of the 4-magnitude belts before the 2005 Jiujiang M5.7 Earthquake. The results show that: (1) Using Delaunay triangulation method, we can fast get the spatial relationship between two neighboring points; (2) using the two neighboring relationships, it can automatically extend to cluster, which carries the key information of seismic belt...
Physics of the Earth and Planetary Interiors, 2008
The eastern boundary of the Sichuan-Yunnan faulted-block in southwestern China, which contains fo... more The eastern boundary of the Sichuan-Yunnan faulted-block in southwestern China, which contains four major fault zones named Xianshuihe, Anninghe, Zemuhe, and Xiaojiang, behaves as a huge left-lateral strike-slip active fault system, where the most frequent seismicity in continental China occurs. To uncover the history of earthquake ruptures of this fault system, we developed an empirical relation between rupture extent and seismic intensity distribution based on data of those earthquakes whose rupture extents and intensity distributions are well known. Through analyzing various types of data, including distributions of damage or intensity of historical earthquakes as well as surface ruptures and aftershock zones of modern earthquakes, we determined systematically the locations and spatial extents of ruptures for 36 main earthquakes, and built up a spatial-temporal pattern of the rupture history of the fault system for the last several hundred years. The spatial-temporal rupture pattern contains information of multi-cycle and broad-scale ruptures, from which we find that for most fault segments, scales of segment-ruptures are time- or cycle-variable and only in two or three cases do scales of segment-ruptures in successive cycles seem to be characteristic. In infrequent cases, several adjacent and connecting fault units may rupture simultaneously, resulting in cascading ruptures. Triggering of ruptures is common along the fault system but differs in various periods even on a single fault zone. Triggered ruptures may not occur on fault-segments adjacent to a preceding rupture of major earthquake but on other segments at some distance away from the preceding rupture, implying that the rupture history determines whether a segment can be triggered or not. Recurrence intervals of major segment-ruptures are longer on the Anninghe and Zemuhe fault zones and on the southernmost segment of the Xiaojiang fault zone than that on the Xianshuihe fault zone and the northern and middle segments of the Xiaojiang fault zone, probably due to the partitioning of slip along major and secondary faults and their complicated fault geometry. Four seismic gaps along the fault system are recognized, where major earthquakes have been absent for a long time.
Описано нейронну мережу (НМ) неперервного часу типу "K-winners-take-all" (KWTA), яка ідентифікує ... more Описано нейронну мережу (НМ) неперервного часу типу "K-winners-take-all" (KWTA), яка ідентифікує К найбільші з-поміж N входів, де керуючий сигнал N K 1 < ≤. Мережа описується рівнянням стану із розривною правою частиною і вихідним рівнянням. Рівняння стану містить шлейф імпульсів, які описуються сумою дельта-функцій Дірака. Проаналізовано існування та єдиність робочих режимів мережі. Головною перевагою мережі порівняно з іншими близькими аналогами є розширення обмежень на швидкість збіжності до робочих режимів. Отримані теоретичні результати ілюструються прикладом комп'ютерного моделювання, який демонструє ефективність мережі. Ключові слова: мережа неперервного часу, нейронна мережа (НМ) типу "K-winnerstake-all" (KWTA), рівняння стану з розривною правою частиною, шлейф імпульсів, дельтафункція Дірака, існування та єдиність.
Science China Earth Sciences, 2011
The N-S trending Xiaojiang fault zone and the NW-SE trending Qujiang-Shiping fault zone are adjac... more The N-S trending Xiaojiang fault zone and the NW-SE trending Qujiang-Shiping fault zone are adjacent active fault systems and seismogenic zones associated with strong and major earthquakes in Yunnan, China. To understand the interaction of the two fault systems, and its probable influence on earthquake occurrences, this paper conducts a synthetic study based on data of active tectonics, historical earthquakes, relocated small earthquakes, GPS station velocities and focal mechanism resolutions. The study makes several conclusions. (1) The active southward motion of the western side of the Xiaojiang fault zone (i.e. the side of the Sichuan-Yunnan block) has a persistent and intensive effect on the Qujiang-Shiping fault zone. The later fault zone has absorbed and transformed the southward motion of the western side of the former fault zone through dextral strike-slip/shearing as well as transverse shortening/thrusting. (2) Along the Xiaojiang fault zone, the present sinistral strike-slip/shearing rate decreases from 10 and 8 mm/a on the northern, central and central-southern segments to 4 mm/a on the southern segment. The decreased rate has been adjusted in the area along and surrounding the Qujiang-Shiping fault zone through reverse-dextral faulting and distributed shearing and shortening. (3) The tectonic-dynamic relation between the Xiaojiang fault zone and the Qujiang-Shiping fault zone is also manifested by a close correlation of earthquake occurrences on the two fault zones. From 1500 to 1850 a sequence of strong and major earthquakes occurred along the Xiaojiang fault zone and its northern neighbor, the Zemuhe fault zone, which was characterized by gradually accelerating strain release, gradually shortening intervals between M⩾7 events, and major releases occurring in the mid to later stages of the sequence. As a response to this sequence, after an 88-year delay, another sequence of 383 years (from 1588 to 1970) of strong and major earthquakes occurred on the Qujiang-Shiping fault zone, and had the same features in accelerating strain release and its temporal course. (4) Since there has been no M⩾7 event for 177 years on the Xiaojiang fault zone, the potential risk of a strong or major earthquake occurring on this fault zone in the future should be noticed and studied further.
Journal of Earth Science, 2010
In this article, firstly, we calculated and analyzed the patterns of Coulomb stress changes induc... more In this article, firstly, we calculated and analyzed the patterns of Coulomb stress changes induced by a sequence of strong earthquakes that occurred in Songpan (松潘), Sichuan (四川) Province in 1973 and 1976, and discovered that the M s 8.0 Wenchuan (汶川) earthquake of 2008 was epicentered in a relevant Coulomb stress triggering zone. This suggests that the Coulomb stress on the middle and southern segments of the Longmenshan (龙门山) fault zone increased after the Songpan sequence of strong earthquakes, and the stress increment might cause the 2008 Wenchuan earthquake having already occurred somewhat ahead of time. Further, we calculated and analyzed Coulomb stress changes coinduced by both the Songpan sequence and the M s 8.0 Wenchuan mainshock. The result shows that the M s 6.4 Qingchuan (青川) earthquake of May 25, 2008 on the northeastern segment of the Longmenshan fault zone was triggered by the Wenchuan mainshock, and that the southwestern segment of the fault zone is also in the stress triggering zone. Besides, the Maoxian (茂县)-Wenchuan fault (i.e., the back-range fault of the Longmenshan fault zone), which extends parallel to the seismogenic fault of the Wenchuan earthquake, is in a shadow zone of the Coulomb stress changes, and therefore, its potential hazard for producing a strong or large earthquake in the near future could be reduced relatively.
Science China Earth Sciences, 2011
ABSTRACT The Kunlun Fault, an active fault on the border between the Bayan Har and Kunlun-Qaidam ... more ABSTRACT The Kunlun Fault, an active fault on the border between the Bayan Har and Kunlun-Qaidam blocks, is one of the major left lateral strike-slip faults in the Tibetan Plateau. Previous research has not reached a consensus on agreeable slip rates along much of its length and the slip rate gradient along the eastern part, both of which play critical roles in a range of models for the eastward extrusion and thickened crust of the Tibetan Plateau. New slip rates have been determined at sites along the eastern part of the Kunlun Fault by dating deposits and measuring atop displaced fluvial terrace risers. Field investigations and interpretation of satellite images reveal geometrical features of the fault and the late Quaternary offset, new earthquake ruptures and surface-rupturing segmentation, from which long-term slip rates and earthquake recurrence intervals on the fault are estimated. The tectonic geomorphology method has determined that the long-term horizontal slip rates on the Tuosuohu, Maqin and Maqu segments from west to east are 11.2±1, 9.3±2, and 4.9±1.3 mm/a while their vertical slip rates are 1.2±0.2, 0.7±0.1, and 0.3 mm/a in the late Quaternary. Results indicate that the slip rates regularly decrease along the eastern ~300 km of the fault from >10 to <5 mm/a. This is consistent with the decrease in the gradient such that at the slip rate break point is at the triple point intersection with the transverse fault, which in turn is transformed to the Awancang Fault. The vector decomposition for this tectonic transformation shows that the western and eastern branches of the Awancang Fault fit the slip-partitioning mode. The slip rate of the southwestern wall is 4.6 mm/a relative to the northeastern wall and the slip direction is 112.1°. The mid-eastern part of the Kunlun Fault can be divided into three independent segments by the A’nyêmaqên double restraining bend and the Xigongzhou intersection zone, which compose the surface rupture segmentation indicators for themselves as well as the ending point of the 1937 M7.5 Tuosuohu earthquake. The average recurrence interval of the characteristic earthquakes are estimated to be 500–1000 a, respectively. The latest earthquake ruptures occurred in AD 1937 on the western Tuosuohu segment, as compared to ~514–534 a BP on the Maqin segment, and ~1055 to 1524 a BP on the Maqu segment. This may indicate a unidirectional migration for surface rupturing earthquakes along the mid-eastern Kunlun Fault related to stress triggered between these segments. Meanwhile, the long-term slip rate is obtained through the single event offset and the recurrence interval, which turn out to be the same results as those determined by the offset tectonic geomorphology method, i.e., the decreasing gradient corresponds to the geometrical bending and the fault’s intersection with the transverse fault. Therefore, the falling slip rate gradient of the mid-eastern Kunlun Fault is mainly caused by eastward extension of the fault and its intersection with the transverse fault.
Our field investigation obtains new evidence of the later Quaternary activity and recent large ea... more Our field investigation obtains new evidence of the later Quaternary activity and recent large earthquake ruptures of the Garzê-Yushu fault. The average left-lateral slip-rate along the fault is determined to be (12 ± 2) mm/a for the last 50000 years from both offset landforms and ages of the correlative sediments. This result is very close to the estimated average left-lateral slip-rate for the Xianshuihe fault, suggesting that the horizontal movement along the northern boundary of the Sichuan-Yunnan active tectonic block and the northeastern boundary of the Qiangtang active tectonic block has been basically harmonious during the later Quaternary period. Remains of ground ruptures of recent large earthquakes have been discovered along all 3 segments of the fault, of which, the 1896 rupture on the northwestern segment is at least 70 km long, and its corresponding earthquake could be of moment magnitude 7.3. The latest rupture on the middle segment of the fault has a length of about 180 km, and was produced by an unknown-age large earthquake that could have a moment magnitude of about 7.7. Along the southeastern segment of the fault, the latest unknown-age rupture is about 65 km long and has a maximum left-lateral coseismic displacement of 5.3 m, and its corresponding earthquake is estimated to be as large as about 7.3 of moment magnitude. Based on relevant investigation, an inference has been drawn that the later two large earthquakes probably occurred in 1854 and 1866, respectively. These demonstrate that the individual segments of the studied Garzê-Yushu fault are all able to produce large earthquakes.
Science in China Series D: Earth Sciences, 2005
The Litang fault zone (LFZ) is an active fault zone within the northwestern Sichuan sub-block. Fi... more The Litang fault zone (LFZ) is an active fault zone within the northwestern Sichuan sub-block. Field investigation reveals new evidence for its late Quaternary offset, neoteric earthquake ruptures and surface-rupturing segmentation, from which long-term slip-rates, characteristic earthquake magnitudes and recurrence intervals on the fault zone are estimated. This study shows that the LFZ consists of three subordinate faults, and they are the northern Maoyaba fault, Litang fault and Kangga-Dewu fault, respectively. All of them are dominated by left-lateral strike-slip with reverse dip-slip component on different segments. Based on offset landforms and ages of relevant deposits collected from seven sites, it is estimated that the average left-lateral slip-rate on the LFZ reaches 4.0±1.0 mm/a in the past 14 ka BP, and vertical (reverse) dip-slip rate in the range of 0.1-1.8 mm/a. Three subordinate faults are independent earthquake rupturing segments, on which the maximum moment magnitude of the characteristic earthquakes is estimated to be 7.0-7.3, and their average recurrence interval to be 500-1000 a. The latest earthquake ruptures occurred 119±2 years ago on the northern Maoyaba fault, about 1890 AD on the Litang fault, and in 1948 AD on the Kangga-Dewu fault, and this may indicate a unidirectional migration for surface rupturing earthquakes along the Litang fault zone, related to stress triggering between the segments.
Science in China Series D: Earth Sciences, 2008
Re-measured GPS data have recently revealed that a broad NE trending dextral shear zone exists in... more Re-measured GPS data have recently revealed that a broad NE trending dextral shear zone exists in the eastern Bayan Har block about 200 km northwest of the Longmenshan thrust on the eastern margin of the Qinghai-Tibet Plateau. The strain rate along this shear zone may reach up to 4-6 mm/a. Our interpretation of satellite images and field observations indicate that this dextral shear zone corresponds to a newly generated NE trending Longriba fault zone that has been ignored before. The northeast segment of the Longriba fault zone consists of two subparallel N54°±5°E trending branch faults about 30 km apart, and late Quaternary offset landforms are well developed along the strands of these two branch faults. The northern branch fault, the Longriqu fault, has relatively large reverse component, while the southern branch fault, the Maoergai fault, is a pure right-lateral strike slip fault. According to vector synthesizing principle, the average right-lateral strike slip rate along the Longriba fault zone in the late Quaternary is calculated to be 5.4±2.0 mm/a, the vertical slip rate to be 0.7 mm/a, and the rate of crustal shortening to be 0.55 mm/a. The discovery of the Longriba fault zone may provide a new insight into the tectonics and dynamics of the eastern margin of the Qinghai-Tibet Plateau. Taken the Longriba fault zone as a boundary, the Bayan Har block is divided into two sub-blocks: the Ahba sub-block in the west and the Longmenshan sub-block in the east. The shortening and uplifting of the Longmenshan sub-block as a whole reflects that both the Longmenshan thrust and Longriba fault zone are subordinated to a back propagated nappe tectonic system that was formed during the southeastward motion of the Bayan Har block owing to intense resistance of the South China block. This nappe tectonic system has become a boundary tectonic type of an active block supporting crustal deformation along the eastern margin of the Qinghai-Tibet Plateau from late Cenozoic till now. The Longriba fault zone is just an active fault zone newly-generated in late Quaternary along this tectonic system.
Science in China Series D: Earth Sciences, 2008
Pure and Applied Geophysics, 2004
Western Sichuan is among the most seismically active regions in southwestern China and is charact... more Western Sichuan is among the most seismically active regions in southwestern China and is characterized by frequent strong (M ‡ 6.5) earthquakes, mainly along the Xianshuihe fault zone. Historical and instrumental seismicity show a temporal pattern of active periods separated by inactive ones, while in space a remarkable epicenter migration has been observed. During the last active period starting in 1893, the sinistral strike-slip Xianshuihe fault of 350 km total length, was entirely broken with the epicenters of successive strong earthquakes migrating along its strike. This pattern is investigated by resolving changes of Coulomb failure function (DCFF) since 1893 and hence the evolution of the stress field in the area during the last 110 years. Coulomb stress changes were calculated assuming that earthquakes can be modeled as static dislocations in an elastic halfspace, and taking into account both the coseismic slip in strong (M ‡ 6.5) earthquakes and the slow tectonic stress buildup associated with major fault segments. The stress change calculations were performed for faults of strike, dip, and rake appropriate to the strong events. We evaluate whether these stress changes brought a given strong earthquake closer to, or sent it farther from, failure. It was found that all strong earthquakes, and moreover, the majority of smaller events for which reliable fault plane solutions are available, have occurred on stress-enhanced fault segments providing a convincing case in which Coulomb stress modeling gives insight into the temporal and spatial manifestation of seismic activity. We extend the stress calculations to the year 2025 and provide an assessment for future seismic hazard by identifying the fault segments that are possible sites of future strong earthquakes.
Journal of Geophysical Research, 2008
Unwanted water, amounting more than 1 million m3, has been injected intermittently at a pumping p... more Unwanted water, amounting more than 1 million m3, has been injected intermittently at a pumping pressure of 2.1–2.9 MPa (over hydrostatic) at 2.6–2.9 km depth within the Rongchang gas field, western Chongqing, China, since July 1988. The injections have induced more than 32,000 surface-recorded earthquakes, including 2 of ML ≥ 5, 14 of ML ≥ 4, and more than 100
Journal of Asian Earth Sciences, 2007
The Ms8.1 Kokoxili, China, earthquake on 14 November, 2001, occurred on the western portion of th... more The Ms8.1 Kokoxili, China, earthquake on 14 November, 2001, occurred on the western portion of the Kunlun fault. By analyzing data from geological surveys and records of historical and modern earthquakes, we know that at least 8 Ms6.9–8.1 earthquakes occurred along the Kunlun fault from 1879 AD to 2000 AD. The spatial arrangement of these ruptures indicates the existence of
Geophysical Journal International, 2007
We performed a numerical simulation of seismic activity along the Xianshuihe fault, a highly acti... more We performed a numerical simulation of seismic activity along the Xianshuihe fault, a highly active strike-slip fault approximately 350 km long, located along the eastern margin area of the Tibetan plateau, southwestern China. Historical earthquake data over the last 300 yr indicate repeated periods of seismic activity, and migration of large earthquakes along the fault during active seismic periods. To understand the characteristics of historical seismicity and to obtain insight into seismic potential, we performed a numerical simulation of slip behaviour along the fault using a 2-D elastic plate model. The friction on the model fault obeys a laboratory-derived rate-and state-dependent friction law, while the long-term slip rates along the fault are assumed to be consistent with geologically and geodetically estimated slip rates. To simulate segmented rupture behaviour we introduced non-uniformity into friction parameters along the fault. The simulation results indicate that seismic rupture is arrested in regions with frictional properties that are highly velocity-strengthening or large values of characteristic slip distance over which frictional stress evolves. In the regions where seismic rupture is arrested, post-seismic sliding occurs, causing time-dependent stress transfer along the fault. Post-seismic slip histories in highly velocity-strengthening regions are well approximated by logarithmic time functions, while those in regions with large characteristic slip distances increase more rapidly in the initial stages of post-seismic sliding. This difference in post-seismic sliding produces the difference in time-dependent stress transfer and, in consequence, the statistical characteristics of earthquake recurrence. Fault interactions near a fault branch point produce complexity in the simulated earthquake sequence. Simulated rupture commonly triggers additional rupture in a neighbouring segment with a time delay of several years. The simulated seismic activity shows good agreement with observational data with respect to the following statistical features: (1) successive seismically active periods are separated by periods of relative quiescence of 100-200 yr duration (2) and the duration of active period is a few tens of years. Strictly speaking, neither the time-nor slip-predictable models are able to describe the simulated local slip history for each fault segment. The ratio of the standard deviation to the average value of the recurrence intervals of simulated earthquakes ranges from 0.05 to 0.22, depending on the fault segment. The cumulative distribution function of the recurrence intervals of simulated earthquakes at each segment approximately obeys a Brownian passage time distribution or a lognormal distribution, which is commonly used in the statistical evaluation of earthquake occurrence.
Acta Seismologica Sinica, 1993
Spatial distribution of sources of strong and large earthquakes on the Xiaojiang fault zone in ea... more Spatial distribution of sources of strong and large earthquakes on the Xiaojiang fault zone in eastern Yunnan is studied according to historical earthquake data. 7 segments of relatively independent sources or basic units of rupture along the fault zone have been identified preliminarily. On every segment, time intervals between main historical earthquakes are generally characterized by "time-predictable" recurrence behavior with indetermination. A statistic model for the time intervals between earthquakes of the fault zone has been preliminarily established. And a mathematical method has been introduced into this paper to reckon average recurrence interval between earthquakes under the condition of having known the size of the last event at a specific segment. Based on these, ranges of the average recurrence intervals given confidence have been estimated for events of various sizes on the fault zone. Further, the author puts forward a real-time probabilistic model that is suitable to analyze seismic potential for individual segments along a fault zone on which earthquake recurrence intervals have been characterized by quasi-time-predictable behavior, and applies this model to calculate conditional probabilities and probability gains of earthquake recurring on the individual segments of the Xiaojiang fault zone during the period from 1991 to 2005. As a consequence, it has shown that two parts of this fault zone, from south of Dongchuan to Songming and from Chengjiang to Huaning, have relatively high likelihoods for strong or large earthquake recurring in the future.
Acta Seismologica Sinica, 2001
This study reveals preliminarily the earthquake behavior of variable rupture-scale on active faul... more This study reveals preliminarily the earthquake behavior of variable rupture-scale on active faults of the Chinese mainland, that is that on an individual fault portion earthquake’s rupture-scale varies cycle to cycle, and hence earthquake’s strength changes with time. The tendency of this variation has no necessity. On defining relative size of rupture scales, a statistical result shows that it is of the lowest probability that ruptures with the same scale occur in two successive cycles. While the rupture’s scale in the preceding cycle is “small”, the probability of the following rupture’s scale being "large" is as many as 0.48. While the rupture’s scale in the preceding cycle is "middle", the probability of the succeeding rupture being "small" or "large" scale is 0.69 or 0.25. While the rupture’s scale in the preceding cycle is "large", the probability must be zero for the following rupture with "large" scale, and is 0.36 or 0.64 for the following rupture with "small" or "middle" scale. The author introduces and improves the cascade-rupturing model, and uses it to describe the variability and complexity of rupture scale on individual fault portions. Basic features of some active strike-slip faults on which cascade ruptures have occurred are summarized. Basing on these features the author proposes principles of cascade-rupture segmentation for this type of faults. As an example to application, the author segments one portion of the Anninghe fault zone, western Sichuan, for its future cascade rupture, and further assesses the probable strength and its corresponding probability of the coming earthquake.
Acta Seismologica Sinica, 1999
To investigate the recurrence behaviors of segment-rupturing earthquakes on active faults of the ... more To investigate the recurrence behaviors of segment-rupturing earthquakes on active faults of the Chinese mainland, this paper analyzes quantitatively earthquake history of 19 fault segments based on earthquake data of multi-cycle recurrences. The result shows that, for these fault segments, earthquake recurring at previous locations is mainly characterized by both quasi-periodic (in a ratio of about 9/19) and time-predictable (in a ratio of about 12/19) behaviors. For the first behavior, intrinsic uncertainty of recurrence interval accounts for 0.15–0.40 of the average interval, and magnitudes of event vary from cycle to cycle within the range of the mean magnitude �0.5. For the second behavior, intrinsic uncertainty of recurrence interval ranges mostly from 0.19 to 0.40 of the average interval, and for successive two cycles the maximum change of event magnitudes is as much as 1.7 magnitude-units. In addition, for a few cases the first behavior coexists along with either the second or the slip-predictable behaviors.
Acta Seismologica Sinica, 1999
For the two main recurrence behaviors of segment-rupturing earthquakes on active faults of the Ch... more For the two main recurrence behaviors of segment-rupturing earthquakes on active faults of the Chinese mainland,this paper establishes corresponding empirical distributions forearthquake recurrence interval. The results show that, for the time-predictable recurrence, the normalized recurrence interval, T/Tt, obeys very well the lognormal distributions: LN (μ1=0.00, σ21 =0. 152), where, T is an observed recurrence interval, and Tt is the average recurrence interval that is correlative with the size of the preceding event. For the quasi-periodic recurrence, the normalized recurrence interval, T/T, follows the lognormal distribution : LN(μq=0.00, σ2q=0.242), where, T is the median of recurrence intervals for various cycles. A statistical test suggests that, there is no significant difference between the latter distribution, built by this paper, and the recurrence interval distribution for the characteristic earthquakes of the Circum-Pacific Plate boundaries (NB model). Accordingly, this paper combines these two distributions into one and obtains a more stable lognormal distribution :LN (μ = 0.00, σ2 = 0.222), for the quasi-periodic recurrence interval.
Earthquake prediction practice and a large number of earthquake cases show that there may be abno... more Earthquake prediction practice and a large number of earthquake cases show that there may be abnormal images of small earthquake belts near the epicenter before strong earthquakes occur. For a static small earthquakes spatial distribution, due to the complexity of exhaustive algorithm, the fast automatic identification method of seismic belts has not yet been realized. Visual identification is still the main method of seismic belt discrimination. Based on the Delaunay triangulation, this paper presents a fast automatic identification method of seismic belts. The effectiveness of this method is proved by a 1000 random points test and an actual example of the 4-magnitude belts before the 2005 Jiujiang M5.7 Earthquake. The results show that: (1) Using Delaunay triangulation method, we can fast get the spatial relationship between two neighboring points; (2) using the two neighboring relationships, it can automatically extend to cluster, which carries the key information of seismic belt...
Physics of the Earth and Planetary Interiors, 2008
The eastern boundary of the Sichuan-Yunnan faulted-block in southwestern China, which contains fo... more The eastern boundary of the Sichuan-Yunnan faulted-block in southwestern China, which contains four major fault zones named Xianshuihe, Anninghe, Zemuhe, and Xiaojiang, behaves as a huge left-lateral strike-slip active fault system, where the most frequent seismicity in continental China occurs. To uncover the history of earthquake ruptures of this fault system, we developed an empirical relation between rupture extent and seismic intensity distribution based on data of those earthquakes whose rupture extents and intensity distributions are well known. Through analyzing various types of data, including distributions of damage or intensity of historical earthquakes as well as surface ruptures and aftershock zones of modern earthquakes, we determined systematically the locations and spatial extents of ruptures for 36 main earthquakes, and built up a spatial-temporal pattern of the rupture history of the fault system for the last several hundred years. The spatial-temporal rupture pattern contains information of multi-cycle and broad-scale ruptures, from which we find that for most fault segments, scales of segment-ruptures are time- or cycle-variable and only in two or three cases do scales of segment-ruptures in successive cycles seem to be characteristic. In infrequent cases, several adjacent and connecting fault units may rupture simultaneously, resulting in cascading ruptures. Triggering of ruptures is common along the fault system but differs in various periods even on a single fault zone. Triggered ruptures may not occur on fault-segments adjacent to a preceding rupture of major earthquake but on other segments at some distance away from the preceding rupture, implying that the rupture history determines whether a segment can be triggered or not. Recurrence intervals of major segment-ruptures are longer on the Anninghe and Zemuhe fault zones and on the southernmost segment of the Xiaojiang fault zone than that on the Xianshuihe fault zone and the northern and middle segments of the Xiaojiang fault zone, probably due to the partitioning of slip along major and secondary faults and their complicated fault geometry. Four seismic gaps along the fault system are recognized, where major earthquakes have been absent for a long time.
Описано нейронну мережу (НМ) неперервного часу типу "K-winners-take-all" (KWTA), яка ідентифікує ... more Описано нейронну мережу (НМ) неперервного часу типу "K-winners-take-all" (KWTA), яка ідентифікує К найбільші з-поміж N входів, де керуючий сигнал N K 1 < ≤. Мережа описується рівнянням стану із розривною правою частиною і вихідним рівнянням. Рівняння стану містить шлейф імпульсів, які описуються сумою дельта-функцій Дірака. Проаналізовано існування та єдиність робочих режимів мережі. Головною перевагою мережі порівняно з іншими близькими аналогами є розширення обмежень на швидкість збіжності до робочих режимів. Отримані теоретичні результати ілюструються прикладом комп'ютерного моделювання, який демонструє ефективність мережі. Ключові слова: мережа неперервного часу, нейронна мережа (НМ) типу "K-winnerstake-all" (KWTA), рівняння стану з розривною правою частиною, шлейф імпульсів, дельтафункція Дірака, існування та єдиність.
Science China Earth Sciences, 2011
The N-S trending Xiaojiang fault zone and the NW-SE trending Qujiang-Shiping fault zone are adjac... more The N-S trending Xiaojiang fault zone and the NW-SE trending Qujiang-Shiping fault zone are adjacent active fault systems and seismogenic zones associated with strong and major earthquakes in Yunnan, China. To understand the interaction of the two fault systems, and its probable influence on earthquake occurrences, this paper conducts a synthetic study based on data of active tectonics, historical earthquakes, relocated small earthquakes, GPS station velocities and focal mechanism resolutions. The study makes several conclusions. (1) The active southward motion of the western side of the Xiaojiang fault zone (i.e. the side of the Sichuan-Yunnan block) has a persistent and intensive effect on the Qujiang-Shiping fault zone. The later fault zone has absorbed and transformed the southward motion of the western side of the former fault zone through dextral strike-slip/shearing as well as transverse shortening/thrusting. (2) Along the Xiaojiang fault zone, the present sinistral strike-slip/shearing rate decreases from 10 and 8 mm/a on the northern, central and central-southern segments to 4 mm/a on the southern segment. The decreased rate has been adjusted in the area along and surrounding the Qujiang-Shiping fault zone through reverse-dextral faulting and distributed shearing and shortening. (3) The tectonic-dynamic relation between the Xiaojiang fault zone and the Qujiang-Shiping fault zone is also manifested by a close correlation of earthquake occurrences on the two fault zones. From 1500 to 1850 a sequence of strong and major earthquakes occurred along the Xiaojiang fault zone and its northern neighbor, the Zemuhe fault zone, which was characterized by gradually accelerating strain release, gradually shortening intervals between M⩾7 events, and major releases occurring in the mid to later stages of the sequence. As a response to this sequence, after an 88-year delay, another sequence of 383 years (from 1588 to 1970) of strong and major earthquakes occurred on the Qujiang-Shiping fault zone, and had the same features in accelerating strain release and its temporal course. (4) Since there has been no M⩾7 event for 177 years on the Xiaojiang fault zone, the potential risk of a strong or major earthquake occurring on this fault zone in the future should be noticed and studied further.
Journal of Earth Science, 2010
In this article, firstly, we calculated and analyzed the patterns of Coulomb stress changes induc... more In this article, firstly, we calculated and analyzed the patterns of Coulomb stress changes induced by a sequence of strong earthquakes that occurred in Songpan (松潘), Sichuan (四川) Province in 1973 and 1976, and discovered that the M s 8.0 Wenchuan (汶川) earthquake of 2008 was epicentered in a relevant Coulomb stress triggering zone. This suggests that the Coulomb stress on the middle and southern segments of the Longmenshan (龙门山) fault zone increased after the Songpan sequence of strong earthquakes, and the stress increment might cause the 2008 Wenchuan earthquake having already occurred somewhat ahead of time. Further, we calculated and analyzed Coulomb stress changes coinduced by both the Songpan sequence and the M s 8.0 Wenchuan mainshock. The result shows that the M s 6.4 Qingchuan (青川) earthquake of May 25, 2008 on the northeastern segment of the Longmenshan fault zone was triggered by the Wenchuan mainshock, and that the southwestern segment of the fault zone is also in the stress triggering zone. Besides, the Maoxian (茂县)-Wenchuan fault (i.e., the back-range fault of the Longmenshan fault zone), which extends parallel to the seismogenic fault of the Wenchuan earthquake, is in a shadow zone of the Coulomb stress changes, and therefore, its potential hazard for producing a strong or large earthquake in the near future could be reduced relatively.
Science China Earth Sciences, 2011
ABSTRACT The Kunlun Fault, an active fault on the border between the Bayan Har and Kunlun-Qaidam ... more ABSTRACT The Kunlun Fault, an active fault on the border between the Bayan Har and Kunlun-Qaidam blocks, is one of the major left lateral strike-slip faults in the Tibetan Plateau. Previous research has not reached a consensus on agreeable slip rates along much of its length and the slip rate gradient along the eastern part, both of which play critical roles in a range of models for the eastward extrusion and thickened crust of the Tibetan Plateau. New slip rates have been determined at sites along the eastern part of the Kunlun Fault by dating deposits and measuring atop displaced fluvial terrace risers. Field investigations and interpretation of satellite images reveal geometrical features of the fault and the late Quaternary offset, new earthquake ruptures and surface-rupturing segmentation, from which long-term slip rates and earthquake recurrence intervals on the fault are estimated. The tectonic geomorphology method has determined that the long-term horizontal slip rates on the Tuosuohu, Maqin and Maqu segments from west to east are 11.2±1, 9.3±2, and 4.9±1.3 mm/a while their vertical slip rates are 1.2±0.2, 0.7±0.1, and 0.3 mm/a in the late Quaternary. Results indicate that the slip rates regularly decrease along the eastern ~300 km of the fault from >10 to <5 mm/a. This is consistent with the decrease in the gradient such that at the slip rate break point is at the triple point intersection with the transverse fault, which in turn is transformed to the Awancang Fault. The vector decomposition for this tectonic transformation shows that the western and eastern branches of the Awancang Fault fit the slip-partitioning mode. The slip rate of the southwestern wall is 4.6 mm/a relative to the northeastern wall and the slip direction is 112.1°. The mid-eastern part of the Kunlun Fault can be divided into three independent segments by the A’nyêmaqên double restraining bend and the Xigongzhou intersection zone, which compose the surface rupture segmentation indicators for themselves as well as the ending point of the 1937 M7.5 Tuosuohu earthquake. The average recurrence interval of the characteristic earthquakes are estimated to be 500–1000 a, respectively. The latest earthquake ruptures occurred in AD 1937 on the western Tuosuohu segment, as compared to ~514–534 a BP on the Maqin segment, and ~1055 to 1524 a BP on the Maqu segment. This may indicate a unidirectional migration for surface rupturing earthquakes along the mid-eastern Kunlun Fault related to stress triggered between these segments. Meanwhile, the long-term slip rate is obtained through the single event offset and the recurrence interval, which turn out to be the same results as those determined by the offset tectonic geomorphology method, i.e., the decreasing gradient corresponds to the geometrical bending and the fault’s intersection with the transverse fault. Therefore, the falling slip rate gradient of the mid-eastern Kunlun Fault is mainly caused by eastward extension of the fault and its intersection with the transverse fault.
Our field investigation obtains new evidence of the later Quaternary activity and recent large ea... more Our field investigation obtains new evidence of the later Quaternary activity and recent large earthquake ruptures of the Garzê-Yushu fault. The average left-lateral slip-rate along the fault is determined to be (12 ± 2) mm/a for the last 50000 years from both offset landforms and ages of the correlative sediments. This result is very close to the estimated average left-lateral slip-rate for the Xianshuihe fault, suggesting that the horizontal movement along the northern boundary of the Sichuan-Yunnan active tectonic block and the northeastern boundary of the Qiangtang active tectonic block has been basically harmonious during the later Quaternary period. Remains of ground ruptures of recent large earthquakes have been discovered along all 3 segments of the fault, of which, the 1896 rupture on the northwestern segment is at least 70 km long, and its corresponding earthquake could be of moment magnitude 7.3. The latest rupture on the middle segment of the fault has a length of about 180 km, and was produced by an unknown-age large earthquake that could have a moment magnitude of about 7.7. Along the southeastern segment of the fault, the latest unknown-age rupture is about 65 km long and has a maximum left-lateral coseismic displacement of 5.3 m, and its corresponding earthquake is estimated to be as large as about 7.3 of moment magnitude. Based on relevant investigation, an inference has been drawn that the later two large earthquakes probably occurred in 1854 and 1866, respectively. These demonstrate that the individual segments of the studied Garzê-Yushu fault are all able to produce large earthquakes.
Science in China Series D: Earth Sciences, 2005
The Litang fault zone (LFZ) is an active fault zone within the northwestern Sichuan sub-block. Fi... more The Litang fault zone (LFZ) is an active fault zone within the northwestern Sichuan sub-block. Field investigation reveals new evidence for its late Quaternary offset, neoteric earthquake ruptures and surface-rupturing segmentation, from which long-term slip-rates, characteristic earthquake magnitudes and recurrence intervals on the fault zone are estimated. This study shows that the LFZ consists of three subordinate faults, and they are the northern Maoyaba fault, Litang fault and Kangga-Dewu fault, respectively. All of them are dominated by left-lateral strike-slip with reverse dip-slip component on different segments. Based on offset landforms and ages of relevant deposits collected from seven sites, it is estimated that the average left-lateral slip-rate on the LFZ reaches 4.0±1.0 mm/a in the past 14 ka BP, and vertical (reverse) dip-slip rate in the range of 0.1-1.8 mm/a. Three subordinate faults are independent earthquake rupturing segments, on which the maximum moment magnitude of the characteristic earthquakes is estimated to be 7.0-7.3, and their average recurrence interval to be 500-1000 a. The latest earthquake ruptures occurred 119±2 years ago on the northern Maoyaba fault, about 1890 AD on the Litang fault, and in 1948 AD on the Kangga-Dewu fault, and this may indicate a unidirectional migration for surface rupturing earthquakes along the Litang fault zone, related to stress triggering between the segments.
Science in China Series D: Earth Sciences, 2008
Re-measured GPS data have recently revealed that a broad NE trending dextral shear zone exists in... more Re-measured GPS data have recently revealed that a broad NE trending dextral shear zone exists in the eastern Bayan Har block about 200 km northwest of the Longmenshan thrust on the eastern margin of the Qinghai-Tibet Plateau. The strain rate along this shear zone may reach up to 4-6 mm/a. Our interpretation of satellite images and field observations indicate that this dextral shear zone corresponds to a newly generated NE trending Longriba fault zone that has been ignored before. The northeast segment of the Longriba fault zone consists of two subparallel N54°±5°E trending branch faults about 30 km apart, and late Quaternary offset landforms are well developed along the strands of these two branch faults. The northern branch fault, the Longriqu fault, has relatively large reverse component, while the southern branch fault, the Maoergai fault, is a pure right-lateral strike slip fault. According to vector synthesizing principle, the average right-lateral strike slip rate along the Longriba fault zone in the late Quaternary is calculated to be 5.4±2.0 mm/a, the vertical slip rate to be 0.7 mm/a, and the rate of crustal shortening to be 0.55 mm/a. The discovery of the Longriba fault zone may provide a new insight into the tectonics and dynamics of the eastern margin of the Qinghai-Tibet Plateau. Taken the Longriba fault zone as a boundary, the Bayan Har block is divided into two sub-blocks: the Ahba sub-block in the west and the Longmenshan sub-block in the east. The shortening and uplifting of the Longmenshan sub-block as a whole reflects that both the Longmenshan thrust and Longriba fault zone are subordinated to a back propagated nappe tectonic system that was formed during the southeastward motion of the Bayan Har block owing to intense resistance of the South China block. This nappe tectonic system has become a boundary tectonic type of an active block supporting crustal deformation along the eastern margin of the Qinghai-Tibet Plateau from late Cenozoic till now. The Longriba fault zone is just an active fault zone newly-generated in late Quaternary along this tectonic system.
Science in China Series D: Earth Sciences, 2008
Pure and Applied Geophysics, 2004
Western Sichuan is among the most seismically active regions in southwestern China and is charact... more Western Sichuan is among the most seismically active regions in southwestern China and is characterized by frequent strong (M ‡ 6.5) earthquakes, mainly along the Xianshuihe fault zone. Historical and instrumental seismicity show a temporal pattern of active periods separated by inactive ones, while in space a remarkable epicenter migration has been observed. During the last active period starting in 1893, the sinistral strike-slip Xianshuihe fault of 350 km total length, was entirely broken with the epicenters of successive strong earthquakes migrating along its strike. This pattern is investigated by resolving changes of Coulomb failure function (DCFF) since 1893 and hence the evolution of the stress field in the area during the last 110 years. Coulomb stress changes were calculated assuming that earthquakes can be modeled as static dislocations in an elastic halfspace, and taking into account both the coseismic slip in strong (M ‡ 6.5) earthquakes and the slow tectonic stress buildup associated with major fault segments. The stress change calculations were performed for faults of strike, dip, and rake appropriate to the strong events. We evaluate whether these stress changes brought a given strong earthquake closer to, or sent it farther from, failure. It was found that all strong earthquakes, and moreover, the majority of smaller events for which reliable fault plane solutions are available, have occurred on stress-enhanced fault segments providing a convincing case in which Coulomb stress modeling gives insight into the temporal and spatial manifestation of seismic activity. We extend the stress calculations to the year 2025 and provide an assessment for future seismic hazard by identifying the fault segments that are possible sites of future strong earthquakes.
Journal of Geophysical Research, 2008
Unwanted water, amounting more than 1 million m3, has been injected intermittently at a pumping p... more Unwanted water, amounting more than 1 million m3, has been injected intermittently at a pumping pressure of 2.1–2.9 MPa (over hydrostatic) at 2.6–2.9 km depth within the Rongchang gas field, western Chongqing, China, since July 1988. The injections have induced more than 32,000 surface-recorded earthquakes, including 2 of ML ≥ 5, 14 of ML ≥ 4, and more than 100
Journal of Asian Earth Sciences, 2007
The Ms8.1 Kokoxili, China, earthquake on 14 November, 2001, occurred on the western portion of th... more The Ms8.1 Kokoxili, China, earthquake on 14 November, 2001, occurred on the western portion of the Kunlun fault. By analyzing data from geological surveys and records of historical and modern earthquakes, we know that at least 8 Ms6.9–8.1 earthquakes occurred along the Kunlun fault from 1879 AD to 2000 AD. The spatial arrangement of these ruptures indicates the existence of
Geophysical Journal International, 2007
We performed a numerical simulation of seismic activity along the Xianshuihe fault, a highly acti... more We performed a numerical simulation of seismic activity along the Xianshuihe fault, a highly active strike-slip fault approximately 350 km long, located along the eastern margin area of the Tibetan plateau, southwestern China. Historical earthquake data over the last 300 yr indicate repeated periods of seismic activity, and migration of large earthquakes along the fault during active seismic periods. To understand the characteristics of historical seismicity and to obtain insight into seismic potential, we performed a numerical simulation of slip behaviour along the fault using a 2-D elastic plate model. The friction on the model fault obeys a laboratory-derived rate-and state-dependent friction law, while the long-term slip rates along the fault are assumed to be consistent with geologically and geodetically estimated slip rates. To simulate segmented rupture behaviour we introduced non-uniformity into friction parameters along the fault. The simulation results indicate that seismic rupture is arrested in regions with frictional properties that are highly velocity-strengthening or large values of characteristic slip distance over which frictional stress evolves. In the regions where seismic rupture is arrested, post-seismic sliding occurs, causing time-dependent stress transfer along the fault. Post-seismic slip histories in highly velocity-strengthening regions are well approximated by logarithmic time functions, while those in regions with large characteristic slip distances increase more rapidly in the initial stages of post-seismic sliding. This difference in post-seismic sliding produces the difference in time-dependent stress transfer and, in consequence, the statistical characteristics of earthquake recurrence. Fault interactions near a fault branch point produce complexity in the simulated earthquake sequence. Simulated rupture commonly triggers additional rupture in a neighbouring segment with a time delay of several years. The simulated seismic activity shows good agreement with observational data with respect to the following statistical features: (1) successive seismically active periods are separated by periods of relative quiescence of 100-200 yr duration (2) and the duration of active period is a few tens of years. Strictly speaking, neither the time-nor slip-predictable models are able to describe the simulated local slip history for each fault segment. The ratio of the standard deviation to the average value of the recurrence intervals of simulated earthquakes ranges from 0.05 to 0.22, depending on the fault segment. The cumulative distribution function of the recurrence intervals of simulated earthquakes at each segment approximately obeys a Brownian passage time distribution or a lognormal distribution, which is commonly used in the statistical evaluation of earthquake occurrence.
Acta Seismologica Sinica, 1993
Spatial distribution of sources of strong and large earthquakes on the Xiaojiang fault zone in ea... more Spatial distribution of sources of strong and large earthquakes on the Xiaojiang fault zone in eastern Yunnan is studied according to historical earthquake data. 7 segments of relatively independent sources or basic units of rupture along the fault zone have been identified preliminarily. On every segment, time intervals between main historical earthquakes are generally characterized by "time-predictable" recurrence behavior with indetermination. A statistic model for the time intervals between earthquakes of the fault zone has been preliminarily established. And a mathematical method has been introduced into this paper to reckon average recurrence interval between earthquakes under the condition of having known the size of the last event at a specific segment. Based on these, ranges of the average recurrence intervals given confidence have been estimated for events of various sizes on the fault zone. Further, the author puts forward a real-time probabilistic model that is suitable to analyze seismic potential for individual segments along a fault zone on which earthquake recurrence intervals have been characterized by quasi-time-predictable behavior, and applies this model to calculate conditional probabilities and probability gains of earthquake recurring on the individual segments of the Xiaojiang fault zone during the period from 1991 to 2005. As a consequence, it has shown that two parts of this fault zone, from south of Dongchuan to Songming and from Chengjiang to Huaning, have relatively high likelihoods for strong or large earthquake recurring in the future.
Acta Seismologica Sinica, 2001
This study reveals preliminarily the earthquake behavior of variable rupture-scale on active faul... more This study reveals preliminarily the earthquake behavior of variable rupture-scale on active faults of the Chinese mainland, that is that on an individual fault portion earthquake’s rupture-scale varies cycle to cycle, and hence earthquake’s strength changes with time. The tendency of this variation has no necessity. On defining relative size of rupture scales, a statistical result shows that it is of the lowest probability that ruptures with the same scale occur in two successive cycles. While the rupture’s scale in the preceding cycle is “small”, the probability of the following rupture’s scale being "large" is as many as 0.48. While the rupture’s scale in the preceding cycle is "middle", the probability of the succeeding rupture being "small" or "large" scale is 0.69 or 0.25. While the rupture’s scale in the preceding cycle is "large", the probability must be zero for the following rupture with "large" scale, and is 0.36 or 0.64 for the following rupture with "small" or "middle" scale. The author introduces and improves the cascade-rupturing model, and uses it to describe the variability and complexity of rupture scale on individual fault portions. Basic features of some active strike-slip faults on which cascade ruptures have occurred are summarized. Basing on these features the author proposes principles of cascade-rupture segmentation for this type of faults. As an example to application, the author segments one portion of the Anninghe fault zone, western Sichuan, for its future cascade rupture, and further assesses the probable strength and its corresponding probability of the coming earthquake.
Acta Seismologica Sinica, 1999
To investigate the recurrence behaviors of segment-rupturing earthquakes on active faults of the ... more To investigate the recurrence behaviors of segment-rupturing earthquakes on active faults of the Chinese mainland, this paper analyzes quantitatively earthquake history of 19 fault segments based on earthquake data of multi-cycle recurrences. The result shows that, for these fault segments, earthquake recurring at previous locations is mainly characterized by both quasi-periodic (in a ratio of about 9/19) and time-predictable (in a ratio of about 12/19) behaviors. For the first behavior, intrinsic uncertainty of recurrence interval accounts for 0.15–0.40 of the average interval, and magnitudes of event vary from cycle to cycle within the range of the mean magnitude �0.5. For the second behavior, intrinsic uncertainty of recurrence interval ranges mostly from 0.19 to 0.40 of the average interval, and for successive two cycles the maximum change of event magnitudes is as much as 1.7 magnitude-units. In addition, for a few cases the first behavior coexists along with either the second or the slip-predictable behaviors.
Acta Seismologica Sinica, 1999
For the two main recurrence behaviors of segment-rupturing earthquakes on active faults of the Ch... more For the two main recurrence behaviors of segment-rupturing earthquakes on active faults of the Chinese mainland,this paper establishes corresponding empirical distributions forearthquake recurrence interval. The results show that, for the time-predictable recurrence, the normalized recurrence interval, T/Tt, obeys very well the lognormal distributions: LN (μ1=0.00, σ21 =0. 152), where, T is an observed recurrence interval, and Tt is the average recurrence interval that is correlative with the size of the preceding event. For the quasi-periodic recurrence, the normalized recurrence interval, T/T, follows the lognormal distribution : LN(μq=0.00, σ2q=0.242), where, T is the median of recurrence intervals for various cycles. A statistical test suggests that, there is no significant difference between the latter distribution, built by this paper, and the recurrence interval distribution for the characteristic earthquakes of the Circum-Pacific Plate boundaries (NB model). Accordingly, this paper combines these two distributions into one and obtains a more stable lognormal distribution :LN (μ = 0.00, σ2 = 0.222), for the quasi-periodic recurrence interval.