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.
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.
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.
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
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
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.
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.
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.
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.
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.
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
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
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.
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.
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.
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Papers by Xueze Wen