2017年九寨沟地震所受历史地震黏弹性库仑应力作用及其后续对周边断层地震危险性的影响

首先对2017年九寨沟M_S7.0地震周边断裂活动和历史地震特征进行了阐述;然后利用黏弹性地壳模型,计算了1933年叠溪地震、1976年松潘震群和2008年汶川地震对2017年九寨沟地震的同震和震后库仑应力作用.该结果显示1933年叠溪地震对九寨沟地震具有延缓作用,而1976年松潘震群和2008年汶川地震对九寨沟地震的黏弹性库仑应力作用为正;随着下地壳和上地幔黏弹性物质的持续作用,前述几次地震总的黏弹性库仑应力在九寨沟地震破裂中心点处负的库仑应力逐渐减弱,而在破裂北段这些库仑应力逐渐转为正值,并促进了九寨沟地震的发生.本文也计算了九寨沟地震后对周边断层的库仑影响,并将此影响值转换为对断层能量积累的影响时间上,结果显示塔藏断裂带西段和中段在内的多条断裂带受到黏弹性库仑应力影响时间值超过10年.将库仑应力影响时间值加入到部分已知离逝时间的断层段上,也得到了这些断层段的未来30年特征地震发生概率.最终结果认为玛沁断裂带、玛曲断裂带、哈南—稻畦子断裂中段和西段等断层段的强震危险性需要重点关注.     

Paleoseismic indications along ‘aseismic’ fault segments in the guadalentín depression (SE Spain)

The Guadalentín Depression, located in SE Spain (Murcia Region), is bounded by two of the main NE-SW master faults of the Eastern Betics Cordilleras: The Lorca-Alhama and the Palomares left-lateral strike-slip faults. Available earthquake data indicate that, in the last 600 years, some sectors of the Lorca-Alhama Fault and the entire sector of the Palomares Fault have not been associated with significant historical seismicity. However, they show a wide range of diagnostic features of earthquake surface displacements on late Pleistocene and Holocene alluvial and colluvial surfaces. Aside from the left-lateral offsets recorded along 045–050 ° master fault strands of the Lorca-Alhama Fault, major paleoseismic surface displacements show different kinematics in relation to the broad orientation of the fault strands: (1) vertical normal displacements along 010–020 ° trending faults mainly preserved as degraded fault scarps of 2.5-1.8 m high (Aljibejo site); and (2) vertical reverse displacements, with average offsets of 0.2 – 1 m, along 065–080 ° subsidiary faults. In this last group, the younger one (Carraclaca Baths site) remains as a fault scarp of 0.8 m height affecting a cascade tufa which was active until the Spanish Roman Period (2nd Century B.C. to 6th Century A.D.). In other cases, reverse offsets resulted in smaller displacements (0.26 m) of paleosols, but show a recurrent behaviour (La Escarihuela site). The strongest earthquakes recorded in the study area did not exceed more than Mb 4.5 or MSK Intensity VIII (historical) with no evidence of coseismic rupture. Therefore, the preliminary data presented here seem to indicate that the paleoseismic activity on both faults is capable of producing coseismic surface displacements, probably reaching magnitudes of at least 6.5. These data show that paleoseismic studies based on geomorphological analyses are a useful tool in the assessment of the relative degree of activity of apparently ‘aseismic’ fault traces.     

Detailed assessment of structural characteristics of Turkish RC building stock for loss assessment models

Assessment of the seismic vulnerability of the building stock in the earthquake-prone Marmara region of Turkey is of growing importance since such information is needed for reliable estimation of the losses that possible future earthquakes are likely to induce. The outcome of such loss assessment exercises can be used in planning of urban/regional-scale earthquake protection strategies; this is a priority in Turkey, particularly following the destructive earthquakes of 1999. Considering the size of the building inventory, Istanbul and its surrounding area is a case for which it is not easy to determine the structural properties and characteristics of the building stock. In this paper, geometrical, functional and material properties of the building stock in the northern Marmara Region, particularly around Istanbul, have been investigated and evaluated for use in loss estimation models and other types of statistic- or probability-based studies. In order to do that, the existing reinforced concrete (RC) stock has been classified as ‘compliant’ or ‘non-compliant’ buildings, dual (frame-wall) or frame structures and emergent or embedded-beam systems. In addition to the statistical parameters such as mean values, standard deviations, etc., probability density functions and their goodness-of-fit have also been investigated for all types of parameters. Functionalities such as purpose of use and floor area properties have been defined. Concrete properties of existing and recently constructed buildings and also characteristics of 220 and 420 MPa types of steel have been documented. Finally, the financial effects of retrofitting operations and damage repair have been investigated.     

Rupture segmentation and assessment of probabilities of seismic potential on the Xiaojiang fault zone

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. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 322–330, 1993.     

鲜水河断裂带上特征地震的初步研究

特征地震是大地震原地重复的重要表现形式.现有资料的初步研究表明,鲜水河断裂带上大地震属特征地震模式,其地震破裂长度、同震位错量以及断层错动方式,在原地保持较长时间的一致性.由于大地震屡屡在原地重复发生,沿断裂特定地段累积位错分布与一次地震的位错相一致,从而导致断层滑动速率的同步变化.本文以1973年炉霍地震为例,研究了鲜水河断裂的特征地震现象.该段的地震活动属特征地震模式,不服从古登堡-里克特的线性震级频度关系.特征地震不仅对断错地貌、滑动速率有重要的影响,由于这种地震模式是以特定震级的大地震为主导,几乎没有中等震级地震发生,这对地震活动性研究也具有重要的意义.      

美国最近三代地震区划图中的断裂震源模型

活断层与古地震定量数据在美国近三代地震区划图中的应用基本上体现了各阶段活断层研究的最新成果,其中断裂震源模型起到了桥梁的作用,并不断得到完善。在1996年地震区划图中引入了特征地震模型与截断的G—R模型,用以表述断层的震级一频度分布关系。在2002年地震区划图中更明确地处理了参数的不确定性,并引入逻辑树概念,同时在特征地震模型中试用了多段破裂模型。在2008年地震区划图中引用了更为广泛的逻辑树来描述地震构造几何形态、地震震级和复发周期的不确定性,其中特征地震模型包括：单段破裂和多段破裂的特征地震模型,以及给定震级的浮动地震模型（或不固定分段模型）。这些经验值得在我国第五代地震区划图的编制工作中借鉴。     

Paleoseismology of the Gazikoy-Saros segment of the North Anatolia fault, northwestern Turkey: Comparison of the historical and paleoseismic records, implications of regional seismic hazard, and models of earthquake recurrence

We excavated five trenches across the North Anatolia fault zone (NAFZ)along the Ganos fault (Gazikoy-Saros segment), which last produced surfacerupture in 1912, near Kavakkoy where the fault enters the Gulf of Saros. The trenches exposed faulted sediments in a flood-plain environment withabundant detrital charcoal and scattered land-snail shells. Twenty-tworadiocarbon dates place constraints on the ages of the exposed sediments,which range from less than a few hundred years to about 6000 years inage. In two closely spaced trenches, we identified five discrete earthquakeevent horizons in the upper 2.5 m of stratigraphy based on abruptupward termination of shear zones, folding, fissuring, and abruptstratigraphic thickening, four of which may corresponded to historicallyrecorded large regional earthquakes. The earliest of the identified eventsoccurs below an unconformity and dates to about 4 ka B.P. The morerecent four events all occurred within the past 1000–1200 years and maycorrespond to large earthquakes in A.D. 824, ca 1354, 1509, 1766 and1912 (Ambraseys and Finkel, 1987, 1991, 1995). In another trench,we identified at least two events that have occurred during the past 500years and probably correspond to the large events of 1766 and 1912. These observations support an average return period of about 250–300years for the Gazikoy-Saros segment of the NAFZ. They also suggest thatthis segment, which is bound both to the east and west by large releasingstepovers, behaves in a quasi-periodic fashion, at least for the past severalsurface ruptures.Most of the 23 mm/yr of dextral shear between Anatolia and Europeobserved by GPS occurs on the North Anatolian fault. We use18 mm/yr and the 250–300 year recurrence rate, as determined fromour trenching and the historical record, to suggest that each of theearthquakes observed in our trenches produced several meters of slip,consistent with their inferred sizes from the extent of historical damage. Considering that Istanbul has not suffered a large nearby event in theMarmara Sea since 1766, we suggest that about 4 m of strain hasaccumulated across faults in the Marmara during these past centuries. Thisis similar to the average slip in many of the large earthquakes on the NorthAnatolian fault this century. If released seismically, this could result in anearthquake in the M 7.2–M 7.6 range, similar to the August and November,1999 earthquakes east of the Marmara Sea.     

FEATURES OF EARTHQUAKE CLUSTERING FROM CALCULATION OF COULOMB STRESS AROUND THE BAYAN HAR BLOCK,TIBETAN PLATEAU

Since 1997, several major earthquakes occurred around the Bayan Har block in the Tibetan plateau, providing an opportunity to further understanding the mechanism of intraplate earthquakes. What is the effect of interactions among these events on the earthquake occurrence pattern is an issue to be addressed. In this article, we use the visco-elastic Coulomb stress changes model to calculate the stress interactions among the historical events close to or large than M_S7.0 since 1893 in the Bayan Har block. We apply the relationships between the slip rate and stress accumulation rate to transform the Coulomb stress changes into the influenced time. Then we remove such influence time from the occurrence years, and analyze the effects of the earthquake interactions on the clustering patterns of the historical earthquakes in the Bayan Har block. The results show that the major earthquakes in the Bayan Har block are characterized by a quasi-period of about 16 years from 1893 to 1973 and a clustering occurrence time period from 1997 to present following a relatively long quiescence period. The Bayan Har block is still in the active period with high probabilities of major quakes. We calculate the conditional probabilities of the rupture segments that did not rupture since 1893 of the boundary faults of the Bayan Har block in the next 30 years. The following faults or fault sections seem to be of major risk:The Maqin segment and the Maqu fault of the East Kunlun fault zone, the Awanang fault, the Luocha segment of the Tazhong fault, the Moxi segment of the Xianshuihe fault, and the Dangjiang fault. Other Fault segments in the Bayan Har block without seismic events since 1893 probably also have hazard of M_S7 earthquakes in the future.     

Paleo-earthquake studies on the eastern section of the Kunlun fault

Introduction East Kunlun active fault is one of the largest sinistral slip fault zones in northern Tibetan Pla-teau. The fault tails primarily after the ancient eastern Kunlun suture zone, which was reactivatedby the northward subduction of the Indian plate beneath the Eurasian plate. The western end of thefault starts near the western flank of the Buxedaban peak in Qinghai Province. The fault then ex-tends eastwards through the Kusai Lake, Xidatan, Dongdatan, Alag Lake, Tuosuo Lak…     

Fractal analysis of normal faults in northwestern Aegean area, Greece

Normal faults within the Ptolemais coal field and large seismogenic faults in the northwestern Aegean remain fractal for displacement values larger than about 1m. The kinematic parameters on reverse drag profiles such as length of rollover, footwall uplift and wavelength of footwall uplift show that all three parameters have a power law relationship, expressed by a c exponent of about 1, with the maximum displacement which take place across the fault. Footwall uplift/hanging wall subsidence ratio is about 1/2.The displacement analysis help us to propose a growth model for larger seismogenic faults in the NW Aegean, as is the ‘Hepiros fault set’ and the ‘Aliakmon fault zone’. Faults within the ‘Aliakmon fault zone’ were independently developed, at the first stages of deformation, by tip line deformation and out-of plane bifurcation, whereas later, deformation continued by segment linkage. One of these faults the ‘Sarakina fault’ was reactivated during the 1995 earthquake to produce a 25 km long surface rupture. A long term slip rate of about 0.3 mm a⁻¹ has been estimated by taking into consideration that over the past 6 Ma a maximum displacement of 1700 m across this fault has taken place.     

安宁河断裂带北段的最新地面活断层与地震潜在能力研究

从最新地面活断层的不连续性,断层滑动速率以及古地震研究的角度讨论安宁河断裂带北段的地震潜在能力,认为不连续的活断层可能成为各自独立的地震破裂单元,从而决定了地震的潜在能力,其中,野鸡洞破裂段的潜在地震能力最强,可达7级。上次地震至今的平静时间已接近古地震的平均重现间隔,因而具有高度的地震危险性     

郯庐断裂带中段全新世活断层的特征滑动行为与特征地震

郯庐断裂带中段全新世活断层由３个独立的破裂段组成。从各破裂段的运动性质、位移分布看，断层的运动属特征地震型滑动。地震活动以强震活动为主，强震具有周期性原地重复发生的特点，且其强度基本相同；中强地震缺失或很少发生；ｂ值在高震级范围内具低ｂ值的非线性关系。这些特点正是特征地震的典型表现．根据郯庐断裂带中段活断层全新世以来的活动特点看，未来该区仍然以特征地震方式活动．按郯庐带的强震复发间隔和各段的最新一次活动时代推算，未来一段时期内新沂－宿迁段复发大震的可能性较大，安丘段次之，莒县－郯城段复发大震的可能性则很小。     

Seismotectonics of the Median Tectonic Line in southwest Japan: Implications for coupling among major fault systems

The relationship between the slip activity and occurrence of historical earthquakes along the Median Tectonic Line (MTL), together with that of the fault systems extending eastward has been examined. The MTL is divided into three segments, each containing diagnostic active faults. No historical earthquakes have been recorded along the central segment, although the segment has faster Quaternary slip rates compared with the other segments that have generated historical earthquakes. This discrepancy between earthquake generation and slip rate can be explained by a microplate model of southwest Japan. The microplate model also provides spatial and temporal coupling of slip on adjacent fault systems. In the context of this model, slip on adjacent faults reduces the normal stress on the MTL. Historical data and paleoseismic evidence indicate that slip on this segment occurs without significant strong ground motion. We interpret this as indicating anomalously slow seismic slip or aseismic slip. Slip on the central segment of the MTL creates transpressional regions at the eastern and western segments where historical earthquakes were recorded. Alternatively, the earthquakes at the eastern and western segments were triggered and concentrated shear stress at the edge of the segments resulted in postseismic slip along the central segment. The sequence of historical events suggests that the MTL characteristically does not produce great earthquakes. The microplate model also provides a tectonic framework for coupling of events among the MTL, the adjacent fault systems and the Nankai trough.     

Seismic Hazard Evaluation in Western Turkey as Revealed by Stress Transfer and Time-dependent Probability Calculations

Western Turkey has a long history of destructive earthquakes that are responsible for the death of thousands of people and which caused devastating damage to the existing infrastructures, and cultural and historical monuments. The recent earthquakes of Izmit (Kocaeli) on 17 August, 1999 (M _w  = 7.4) and Düzce (M _w  = 7.2) on 12 November, 1999, which occurred in the neighboring fault segments along the North Anatolian Fault (NAF), were catastrophic ones for the Marmara region and surroundings in NW Turkey. Stress transfer between the two adjacent fault segments successfully explained the temporal proximity of these events. Similar evidence is also provided from recent studies dealing with successive strong events occurrence along the NAF and parts of the Aegean Sea; in that changes in the stress field due to the coseismic displacement of the stronger events influence the occurrence of the next events of comparable size by advancing their occurrence time and delimiting their occurrence place. In the present study the evolution of the stress field since the beginning of the twentieth century in the territory of the eastern Aegean Sea and western Turkey is examined, in an attempt to test whether the history of cumulative changes in stress can explain the spatial and temporal occurrence patterns of large earthquakes in this area. Coulomb stress changes are calculated assuming that earthquakes can be modeled as static dislocations in elastic half space, taking into account both the coseismic slip in large (M ≥ 6.5) earthquakes and the slow tectonic stress buildup along the major fault segments. The stress change calculations were performed for strike-slip and normal faults. In each stage of the evolutionary model the stress field is calculated according to the strike, dip, and rake angles of the next large event, whose triggering is inspected, and the possible sites for future strong earthquakes can be assessed. A new insight on the evaluation of future seismic hazards is given by translating the calculated stress changes into earthquake probability using an earthquake nucleation constitutive relation, which includes permanent and transient effects of the sudden stress changes.     

Study on Integrated Recurrence Behaviors of Strong Earthquakes Along Entire Active Fault Zones in the Sichuan-Yunnan Region, China

Based on historical earthquake data, we use statistical methods to study integrated recurrence behaviors of strong earthquakes along 7 selected active fault zones in the Sichuan-Yunnan region. The results show that recurrences of strong earthquakes in the 7 fault zones display near-random, random and clustering behaviors. The recurrence processes are never quasiperiodic, and are neither strength-time nor time-strength dependent. The more independent segments for strong earthquake rupturing a fault zone has, the more complicated the corresponding recurrence process is. And relatively active periods and quiescent periods for earthquake activity occur alternatively. Within the active periods, the distribution of recurrence time intervals between earthquakes has relatively large discretion, and can be modelled well by a Weibull distribution. The time distribution of the quiescent periods has relatively small discretion, and can be approximately described by some distributions as the normal. Both the durations of the active periods and the numbers of strong earthquakes within the active periods vary obviously cycle by cycle, leading to the relatively active periods having never repeated quasi-periodically. Therefore, the probabilistic assessment for middle- and longterm seismic hazard for entireties of active fault zones based on data of historical strong earthquakes on the fault zones still faces difficulty.     

Inverse analysis of deformation mechanism by geodetic surveys−a case study

In 1988 two large earthquakes with magnitude of Ms 7.6 and Ms 7.2 occurred in Lancang-Genma area, Southwest China. This paper discusses the determination of the spatial distribution of fault slip caused by the earthquakes using geodetic surveys. The prior information obtained from geological surveys and seismological investigations was used to determine the geometry of the fault plane and the average fault slip. The smooth constraints on the fault slips have been described by a normal distribution with hyperparameters, which are incorporated in the inversion analysis with a Bayesian model. Akaike’s Bayesian Information Criterion (ABIC) is used to get the optimal values of hyperparameters. Once the hyperparameters are determined, the maximum likelihood method is employed to estimate the patterns of a fault slip. Based on the results of inverse analysis monitoring geodetic surveys can be properly designed and conducted to obtain crust deformations and predict potential earthquake sources.     

断层横向构造在逆冲型地震破裂中的作用——以汶川地震小鱼洞断层为例

大地震破裂大多由横向构造(如阶区、弯曲和分叉)所分割的多个段落组成.2008年5·12汶川地震破裂沿北东走向上穿过了多个横向构造部位,特别在震中北东45 km的位置,小鱼洞断层、北川断层和彭灌断层三者之间呈现复杂的断裂切割相交关系.复杂断层几何结构对破裂的扩展是有抑制还是促进的作用？在相交的断裂段之间是否存在最优的破裂顺序？本文以库仑应力分析为手段,探讨在汶川同震破裂初始30 s内,破裂在多分支断裂中选择扩展路径时的可能应力相互作用.库仑应力分析显示:如果北川断层先发生破裂,其滑动对小鱼洞断层和彭灌断层均产生强烈负应力的抑制作用,而彭灌断层的滑动却反而对小鱼洞断层和北川断层浅部有强烈正应力的促进作用.因此,从准静态应力分析角度,彭灌断层先于北川断层发生破裂的可能性较大,这一破裂顺序与小鱼洞断层参与同震破裂过程的事实相符.此外,小鱼洞断层在链接北川和彭灌断层的同震位移中可能起到桥梁作用,但非静态应力的影响.横向构造在逆冲型地震破裂扩展过程中起到的牵引作用使得逆冲型地震破裂能够比走滑型地震跨越更宽的阶区.横向构造是逆冲断裂带内广泛发育的构成单元,因此在地震危险性分析的最大潜在震级测算中应该考虑其作用.     

SIMULATION OF SEISMIC RISK IN THE DALIANGSHAN SUB-BLOCK AND ADJACENT AREAS USING THE NONLINEAR FRICTION FEM METHOD

Most earthquakes result from fault activity under heterogeneous loading and complex physical properties, also affected by fault structure and interaction between faults. Such a complicated mechanism makes often failures of the "seismic gap" theory in the effort of medium-and long-term earthquake prediction. This study attempts to address this issue using the finite element method(FEM).The friction behavior of faults can be used to simulate the non-uniformity of rupture processes of the seismogenic structure. So we use the FEM containing non-linear friction to simulate fault ruptures in the Daliangshan sub-block and adjacent areas, and compare the results with time-space evolution of historical M_S ≥ 7 earthquakes since 1840 in this region. In the simulation, the sequence of large-batch fault contact nodes change from "stick state" to "slip state" in short time, which mimics the sudden fault slip and the occurrence of major earthquakes. The results show that the fault breaking lengths from simulation are largely consistent with the magnitudes of historical earthquakes in the study area, such as the 1850 Puge-Xichang M_S7.5, and 1887 Shiping M_S7.0 earthquakes. The simulation also shows the development of seismic gaps and "gap breaks" by major earthquakes on the Xianshuihe fault, such as 1955 Kangding M_S7.5 earthquake. Especially, the results illustrated the very long time of the seismogenic process of the 2008 Wenchuan M_S8.0 earthquake, and the corresponding sudden big rupture along the Longmenshan Fault, which is very similar to the observed surface rupture and very long incubation time and sudden co-seismic process. Then, this simulation is further applied to long-term earthquake prediction for the study area by calculation on a much longer time. The simulation results suggest that the Xiaojiang fault and the Zemuhe fault have relatively higher seismic risk, while moderate-sized earthquakes might occur on the Daliangshan fault and the Aninghe fault, and major earthquakes might rupture the northern segment of the Xianshuihe fault in a much longer time.     

Detecting co-seismic displacements in glaciated regions: An example from the great November 2002 Denali earthquake using SPOT horizontal offsets

We use SPOT image pairs to determine horizontal offsets associated with the Mw 7.9 November 2002 Denali earthquake in the vicinity of Slate Creek, AK. Field measurements and aerial photographs are used to further characterize the geometry of the surface rupture. Aerial photographs show that shear localization occurs where the rupture trace is linear, and distributed off-fault deformation is common at fault bends and step-overs, or at geologic contacts between rock, glacial sediments, and ice. The displacement field is generated using a sub-pixel cross correlation technique between SPOT images taken before and after the earthquake. We identify the effects of glacier motion in order to isolate the tectonic displacements associated with the Denali earthquake. The resulting horizontal displacement field shows an along-strike variation in dextral shear, with a maximum of approximately 7.5 m in the east near 144° 52′W, which decreases to about 5 m to the west near 145° 45′W. If the November 2002 earthquake represents the long-term behavior of the Denali fault, it implies a westward decrease in the long-term dextral slip rate. A possible mechanism to accommodate the westward decreasing slip on the Denali fault is to transfer fault slip to adjacent east-trending contractional structures in the western region of the central Alaskan Range.