The features of multiple fractures associated with the great Haiyuan 8.5 magnitude earthquake of 1920

It is deduced on the basis of field investigation that the total length of the stratigraphic fault associated with the great Haiyuan 8.5 magnitude earthquake of 1920 was 225 km. This fault was formed by 6 secondary faults with different geometric parameters, which align regularly inen echelon arrangement. Each secondary fault can be divided into three segments with different characteristics of deformation where the middle segment was mainly of the horizontal strike—slip fault while another two segments the vertical deformation as shown by the features of reverse or normal faults. It is also shown by the data of vertical and horizontal displacements that the horizontal displacement approached a maximum at the middle segment for each secondary fault and gradually decreased toward and finally disappeared at both ends of each segment while in contrast the vertical displacement was minimum at the middle and became large at both ends of the segment. The feature of the multiple peaks appeared in the deformation as shown by the earthquake displacements along the whole fault. This feature indicates that the 6 secondary faults associated with the great Haiyuan earthquake were the horizontal interrupted planes (i.e., dislocation surface) which were independent on each other, and hence each dislocation surface may represent an independent secondary fracture event of the earthquake. We thus think that the 6 relatively independent secondary events which occurred successfully might result in the great 8.5 magnitude Haiyuan earthquake. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 21–31, 1991. This project is sponsored by the Chinese Joint Seismological Science Foundation.     

Foundation–structure systems over a rupturing normal fault: Part II. Analysis of the Kocaeli case histories

Motivated by the observed (successful and unsuccessful) performance of numerous structures on top of, or immediately next to a normal fault that ruptured during the Kocaeli 1999 earthquake, this paper: (i) develops a two-step finite element methodology to study the propagation of a fault rupture through soil and its interplay with the foundation–structure system, denoted hereafter “Fault Rupture–Soil– Foundation–Structure Interaction” (FR–SFSI), (ii) provides validation of the developed methodology through successful Class “A” predictions of centrifuge model tests, and (iii) applies the centrifuge-validated methodology to study one-by-one the Kocaeli case histories of the first paper (Part I). It is shown that the presence of a structure on top of an outcropping fault may have a significant influence on the rupture path: with heavy structures founded on continuous and rigid foundations, the fault rupture diverts substantially and may avoid rupturing underneath the structure. The latter undergoes rigid body rotation, with its foundation sometimes loosing contact with the bearing soil, but in most cases retaining its structural integrity. In stark contrast, buildings on isolated footings and, perhaps surprisingly, piles exert a smaller diversion of the rupture which is thus likely to outcrop between the footings or pile caps; the latter may thus undergo devastating differential displacements. It is shown that structures in the vicinity of faults can be designed to survive significant dislocations. The “secret” of successful performance lies on the continuity, stiffness, and rigidity of the foundation.     

Relation of surface movements in West Bohemia to earthquake swarms

GPS observations in the Western Bohemia/Vogtland earthquake swarm region revealed indications of horizontal displacements of low amplitude, and no clear long-term trend in 1993–2007. On the other hand, in 1998–2001 there was relatively significant active movement along NNE-SSW oriented line that we called the “Cheb-Kraslice GPS Boundary” (ChKB), identical with an important limitation of earthquake activity. The most impressive were dextral (right-lateral) movements in the 1998–1999 period followed by reverse sinistral (left-lateral) movements in 1999–2000 that correlate with prevailing motion defined by fault plane solutions of the Autumn 2000 earthquake swarm. Before the February 2004 micro-swarm, two points located on opposite sides of the Mariánské Lázně fault showed extension in the order of about 7 mm in the same NNE-SSW direction of ChKB. The new NOKO permanent GPS station in Novy Kostel showed the peak-to-peak vertical changes up to 10 mm before and during the February 2007 micro-swarm. Annual precise levelling campaigns in the local network around Novy Kostel revealed regular vertical displacements during the 1994, 1997 and 2000 earthquake swarms. The points around the Novy Kostel seismological station showed uplift during the active periods, including the micro-swarm February 2004. However, no such indication was observed on levelling points in the period of the February 2007 swarm. Long-term vertical displacements depend on the same direction NNE-SSW (ChKB) as the GPS displacements. Both geodetic techniques have revealed oscillating displacements, GPS horizontal, and levelling vertical, rather than any long-term trends in the study period 1993–2007. The displacements exhibited significant spatial and temporal relation to tectonic activity (earthquake swarms) including their coincidence with the seismologically determined sense of motion along the fault plane during earthquakes.     

Geological setting of the 8 October 2005 Kashmir earthquake

The source of the 8 October 2005 earthquake of M 7.6 was the northwest-striking Balakot–Bagh (B–B) fault, which had been mapped by the Geological Survey of Pakistan prior to the earthquake but had not been recognized as active except for a 16-km section near Muzaffarabad. The fault follows the Indus–Kohistan Seismic Zone (IKSZ); both cut across and locally offset the Hazara–Kashmir Syntaxis defined by the Main Boundary and Panjal thrusts. The fault has no expression in facies of the Miocene–Pleistocene Siwalik Group but does offset late Pleistocene terrace surfaces in Pakistan-administered Jammu-Kashmir. Two en-échelon anticlines near Muzaffarabad and Balakot expose Precambrian Muzaffarabad Limestone and are cut by the B–B fault on their southwest sides, suggesting that folding and exposure of Precambrian rocks by erosion accompanied Quaternary displacement along the fault. The B–B fault has reverse separation, northeast side up; uplift of the northeast side accompanied displacement, producing higher topography and steeper stream gradients northeast of the fault. No surface expression of the B–B fault has been found northwest of the syntaxis, although the IKSZ and steeper stream gradients continue at least as far as the Indus River, the site of the Pattan earthquake of M 6.2 in 1974. To the southeast, northwest-striking faults were mapped by the Geological Survey of Pakistan. One of these faults, the Riasi thrust, cuts across the southwest flank of an anticline exposing Precambrian limestone. Farther southeast, in Indian-administered territory, Holocene activity on the Riasi thrust has been described. In the Kangra reentrant still farther southeast, active faulting may follow the Soan thrust, along which Holocene and Pleistocene offsets have been described. The Soan thrust, rather than the south flank of the Janauri anticline, may represent the surface projection of the 1905 Kangra earthquake of M 7.8.     

Surface rupture zone of the 1303 Hongtong M=8 earthquake, Shanxi Province

Based on the latest displacement of Huoshan piedmont fault, Mianshan west-side fault and Taigu fault obtained from the beginning of 1990‘s up to the present, the characteristics of distribution and displacement of surface rupture zone of the 1303 Hongtong M = 8 earthquake, Shanxi Province are synthesized and discussed in the paper. If Taigu fault, Mianshan west-side fault and Huoshan piedmont fault were contemporarily active during the 1303 Hongtong M = 8 earthquake, the surface rupture zone would be 160 km long and could be divided into 3 segments, that is, the 50-km-long Huoshan piedmont fault segment, 35-km-long Mianshan west-side fault segment and 70-km-long Taigu fault segment, respectively. Among them, there exist 4 km and 8 km step regions. The surface rupture zone exhibits right-lateral features. The displacements of northern and central segments are respectively 6～7 m and the southern segment has the maximum displacement of 10 m. The single basin-boundary fault of Shanxi fault-depression system usually corresponds to M ≈ 7 earthquake, while this great earthquake (M = 8) broke through the obstacle between two basins. It shows that the surface rupture scale of great earthquake is changeable.     

Spatio-temporal evolution of Yellowstone deformation between 1992 and 2009 from InSAR and GPS observations

In this study, the spatio-temporal evolution of Yellowstone deformation between 1992 and 2009 is monitored using interferometric synthetic aperture radar (InSAR) data acquired by the European Remote-Sensing Satellites (ERS-1 and ERS-2) and the Environmental Satellite (ENVISAT). These data are combined with continuous global positioning system (GPS) measurements to identify four discrete episodes of caldera subsidence and uplift, these episodes are: 1992–1995 (subsidence of 2.7 cm/year), 1996–2000 (subsidence of 0.5 cm/year, with local uplift of 1.7 cm/year at Norris), 2000–2004 (subsidence of 0.7 cm/year, with local uplift of 0.6 cm/year at Norris), and 2004–2009 (uplift of 3–8 cm/year, with local subsidence of 1–4 cm/year at Norris). We construct the full three-dimensional velocity field of Yellowstone deformation for 2005–2006 from ascending and descending ENVISAT orbits. The InSAR three-dimensional velocity field and three-component GPS measurements indicate that the majority of the observed deformation (3–8 cm/year) across the Yellowstone caldera and near Norris Geyser Basin (NGB) occurred in the vertical direction between the summers of 2005 and 2006. During this time, significant lateral displacements of 3–7 cm/year also occurred in the east–west direction at the southeastern and western rims of the Yellowstone caldera and in the area between Hebgen Lake and NGB. Minor north–south displacements of about 0.2 cm/year also occurred, however, in the southwestern section of the caldera and near Yellowstone Lake during the same period. The calculated three-dimensional velocity field for 2005–2006 implies the existence of two pressure-point sources, beneath the two structural resurgent domes in the Yellowstone caldera, connected by a planar conduit, rather than a single, large sill as proposed in previous studies. Furthermore, no measurable displacements occurred along any fault zone across the caldera during the entire period of observation (1992–2009). Therefore, we infer that magmatic and hydrothermal processes beneath the Yellowstone caldera and NGB were the main sources of deformation.     

Fault rupture–foundation interaction: selected case histories

The 1999 earthquakes in Turkey and Taiwan, offering a variety of case histories with structures subjected to large tectonic displacements, have refueled the interest of the earthquake engineering community on the subject. While several structures were severely damaged or even collapsed, there were numerous examples of satisfactory performance. Even more astonishingly, in specific cases the surface fault rupture was effectively diverted due to the presence of a structure. For the purpose of developing deeper insights into the main mechanisms controlling this fascinating interplay, this article documents selected field case histories of fault rupture–foundation interaction from (a) the M_w 7.4 Kocaeli (August 17) 1999 earthquake in Turkey, (b) the M_w 7.1 Düzce-Bolu (November 12) 1999 earthquake in Turkey, (c) the M_w 7.6 Chi–Chi (September 21) 1999 earthquake in Taiwan, and (d) surface faulting in Mount Etna. A subset of the case histories presented herein is analysed numerically, using the methods developed in the companion paper. It is shown that relatively “heavy” or stiff structures supported by continuous and rigid foundations may divert the fault rupture. Such structures are subjected to rigid body rotation, without substantial structural distress. In contrast, structures on structurally–resilient foundation systems or on isolated supports are prone to substantial damage.     

Earthquake source as an object of geological study

The paper presents the results of long-term geological-geophysical studies of the author, which have a direct relationship to the structure and development of the sources of the strong earthquakes that occurred on the territory of Mongolia and the Baikal rift zone. They left imprints in the form of seismic dislocations in the near-surface layers or in the form of thermally treated rocks (pseudo-tachylites), considered as evidence of the manifestation of seismogenic motions in the segments of seismoactive faults at depths of 10–20 km. It was revealed that in the regions of the manifestation of denudation shear on the Earth’s surface with a length of many kilometers it is possible to identify the deep fragments of faults, in which previously the signs of rapid seismogenic motions along the faults had been manifested. Such deep fragments are revealed from the presence of friction planes, covered by the finest glass films, which arose under the strong frictional heating of rocks before the stage of melting. In this way, the possibility of studying such sections of zones of seismo-generating faults is validated, considering them as deep fragments of earthquake sources, which occurred many million years ago. New information on the instrumental measurements of the velocity of motions in the seismoactive faults is also discussed in the work. The ideas on the mechanisms of generating seismic vibrations in the fault zones are presented. The conclusion that the lower segments of faults in the source regions of earthquakes are capable of penetrating rapidly at depths of 25–40 km, where the viscoplastic deformations of rocks predominate, causing their nonlinear behavior, is substantiated. On the development of the new models of earthquake sources, more adequate to geological conditions, it is expedient to consider the ideas presented in the paper     

滇西南地区孟连断裂晚第四纪新活动特征初步研究

孟连断裂位于云南省西南部与缅甸交界地带,是川滇菱形块体南部一条规模较大的活动断裂带,总体呈NEE向延伸,长约90km,走向N70°E,倾向NW,倾角50°~60°,断裂晚第四纪活动较强烈,以左旋走滑为主,兼具有倾滑特征。通过卫星影像解译和野外调查发现,其断错地貌主要以线性断层崖为主,高度不等,其次为断层谷地、断层沟槽和断层垭口地貌,冲沟及阶地的水平位移多在几十米至几百米之间。在孟连县城西侧开挖的大型探槽中,揭露出多条断层,通过分析剖面和14C测年结果认为,孟连断裂晚第四纪发生过4次古地震事件,除最早一次年代较久远以外,其他3次均发生在全新世中晚期以来,最近一次古地震事件的年代为(1 860±30)~(1 090±30)a B.P.。     

Origin of mass faulting during seismic activation in the Central Kuznetsk basin

In 2005, the low magnitude shallow hypocenter swarm seismic activation occurred in the central part of Kuznetsk Depression. It continues until today. The main objects of implemented field works were numerous ruptures appearing on the surface in the vicinity of the town of Polysayevo during the activation period. In addition to chaotically distributed subsidences, slumps, and cracks related to surface saggings above worked mine fields, linear fractures of the Earth’s surface were found. These fractures form regular structural parageneses and comprise a relatively large system of 7.6 km total length. Regular structural parageneses and displacements along the faults of up to 10 cm in amplitude allow us to consider them as surface tectonic fractures. The depth of earthquake hypocenters, based on instrumental data, reaches 5 km; i.e., quakes occur significantly deeper than mine fields, which are located down to a 500 m depth. It is possible to suppose that the summarized impulse effect of seismic activation had led to formation of seismotectonic deformations in the zone of an already existing fault. The difference of the described fractures from typically seismotectonic ruptures is their gradual, slow formation. Approximate time of the start of formation for the studied fractures is several years ago, with continuous renewal up to the present. Another difference of the surface fractures is their remote positions at the distance of 1–2 km west of the epicentral area of the earthquakes swarm.     

Aseismic negative dislocation model and deformation analysis of crustal horizontal movement during 1999——2001 in the northeast margin of Qinghai-Xizang block

Through numerical simulation for GPS data, aseism/c negative dislocation model for crustal horizontal movement during 1999-2001 in the northeast margin of Qinghai-Xizang block is presented, combined with the spatial distri-bution of apparent strain field in this area, the characteristics of motion and deformation of active blocks and their boundary faults, together with the place and intensity of strain accumulation are analyzed. It is shown that: a) 9 active blocks appeared totally clockwise motion from eastward by north to eastward by south. Obvious sinistral strike-slip and NE-NEE relative compressive motion between the blocks separated by Qilianshan-Haiyuan fault zone was discovered; b) 20 fault segments (most of them showed compression) locked the relative motion between blocks to varying degrees, among the total, the mid-east segment of Qilianshan fault (containing the place where it meets Riyueshan-Lajishan fault) and the place where it meets Haiyuan fault and Zhuanglanghe fault, more favored accumulation of strain. Moreover, the region where Riyueshan-Lajishan fault meets north boundary of Qaidam block may have strain accumulation to some degree, c) Obtained magnitude of block velocities and locking of their boundaries were less than relevant results for observation in the period of 1993-1999.     

山西高原六棱山北麓断裂晚第四纪运动学特征初步研究

六棱山北麓断裂是山西地堑系北端张性构造区中的一条控制性断裂，总体走向北东东、倾向北北西，是一条至今仍在活动的倾滑正断裂，控制阳原盆地的形成和发展。在１９９３年和１９９４年的中日合作研究中，我们对断裂分段特征进行了研究，并用Ａｕｔｏ－ｌｅｖｅｌ仪器对这一条断裂晚第四纪不同时期的断错地貌面的位错量进行了测量，对这些地貌面的年龄进行了测定，得到该断裂带晚更新世晚期至全新世时期的平均垂直滑动速率为０．４３～０．７５ｍｍ／ａ。关键词     

云南中甸-大具断裂马家村-大具段古地震初步研究

中甸-大具断裂马家村-大具段位于哈巴雪山北麓及玉龙雪山以北的大具盆地内,总体走向310°～320°,根据卫星影像解译和详细的野外地质地貌调查,认为中甸-大具断裂马家村-大具段自第四纪以来长期活动,横跨断裂的水系右旋位错量可分为8.5～12m、22m左右、47m左右、200～280m、500～510m和1000m左右6个等级。在大具盆地内发现了长约600m的地震地表破裂带,这是该断层段在全新世活动的直接地质证据,在破裂带南东端附近开挖的探槽揭示出自晚更新世以来断裂存在三期活动,可能对应3次地震事件,结合前人在该断裂段获得的地质剖面和断错地貌面测年结果,分析认为马家村-大具段自晚更新世以来至少发生了3次古地震事件,发生时间分别为4910～45 a BP、7000 a BP左右和32.93～19.96ka BP,利用垂直同震位移值估算了水平同震位移量,最终得出每次地震事件的震级为7.5级左右。     

Stress Rotation in the Kachchh Rift Zone, Gujarat, India

Double difference relocations of the 1402 Kachchh events (2001–2006) clearly delineate two fault zones viz. south-dipping North Wagad fault (NWF) and almost vertical Gedi fault (GF). The relocated focal depths delineate a marked variation of 4 and 7 km in the brittle-ductile transition depths beneath GF and NWF, respectively. The focal mechanism solutions of 464 aftershocks (using 8–12 first motions) show that the focal mechanisms ranged between pure reverse and pure strike-slip except for a few pure dip-slip solutions. The stress inversions performed for five rectangular zones across the Kachchh rift reveal both clockwise and anticlockwise rotation (7–32°) in the σ₁ orientation within the rupture zone, favoring a heterogeneous stress regime with an average N-S fault normal compression. This rotation may be attributed to the presence of crustal mafic intrusives (5–35 km depth) in the rupture zone of the 2001 Bhuj main shock. Results suggest a relatively homogeneous stress regime in the GF zone favoring strike-slip motion, with a fault normal N-S compression.     

Rigidity of the fault zones in the Earth’s crust estimated from seismic data

Nonlinear effects in seismic wave propagation are analyzed to determine the mechanical rigidity of different-order faults that thread the tectonic structures in the central part of the East European platform (Moscow syneclise and Voronezh Crystalline Massif) and the fault zones of the Balapan and Degelen mountain regions in Kazakhstan (the Degelen magmatic node in the Central Chingiz zone). The dependency of the rigidity of the fault zone on the fault’s length is obtained. The rigidity of the tectonic structures is found to experience well-expressed temporal variations with periods of 13–15 days, 27–32 days, and about one year. In the different-order fault zones, the amplitudes of both normal k _n and the shear k _s rigidity for semimonthly, monthly, and annual variations can span a factor of 1.3, 1.5, and 2.5, respectively.     

Nitrogen uptake and denitrification in restored and unrestored streams in urban Maryland, USA

There is growing interest in rates of nitrate uptake and denitrification in restored streams to better understand the effects of restoration on nitrogen processing. This study quantified nitrate uptake in two restored and two unrestored streams in Baltimore, Maryland, USA using nitrate additions, denitrification enzyme assays, and a ¹⁵N isotope tracer addition in one of the urban restored streams, Minebank Run. Restoration included either incorporation of stormwater ponds below a storm drain and catch basins to attenuate flow or hydrologic “reconnection” of a stream channel to its floodplain. Stream restoration was conducted for restoring aging sanitary and bridge infrastructure and introducing some stormwater management in watersheds developed prior to current regulations. Denitrification potential in sediments was variable across streams, whereas nitrate uptake length appeared to be significantly correlated to surface water velocity, which was low in the restored streams during summer baseflow conditions. Uptake length of NO₃ ⁻–N in Minebank Run estimated by ¹⁵N tracer addition was 556 m. Whole stream denitrification rates in Minebank Run were 153 mg NO₃ ⁻–N m⁻² day⁻¹, and approximately 40% of the daily load of nitrate was estimated to be removed via denitrification over a distance of 220.5 m in a stream reach designed to be hydrologically “connected” to its floodplain. Increased hydrologic residence time in Minebank Run during baseflow likely influenced rates of whole stream denitrification, suggesting that hydrologic residence time may be a key factor influencing N uptake and denitrification. Restoration approaches that increase hydrologic “connectivity” with hyporheic sediments and increase hydrologic residence time may be useful for stimulating denitrification. More work is necessary, however, to examine changes in denitrification rates in restored streams across different seasons, variable N loads, and in response to the “flashy” hydrologic flow conditions during storms common in urban streams.     

Experimental evidence for direct penetration of ULF waves from the solar wind and their possible effect on acceleration of radiation belt electrons

The event of March 12–19, 2009, when a moderately high-speed solar wind stream flew around the Earth’s magnetosphere and carried millihertz ultralow-frequency (ULF) waves, has been analyzed. The stream caused a weak magnetic storm (D _{st min} = −28 nT). Since March 13, fluxes of energetic (up to relativistic) electrons started increasing in the magnetosphere. Comparison of the spectra of ULF oscillations observed in the solar wind and magnetosphere and on the Earth’s surface indicated that a stable common spectral peak was present at frequencies of 3–4 mHz. This fact is interpreted as evidence that waves penetrated directly from the solar wind into the magnetosphere. Possible scenarios describing the participation of oscillations in the acceleration of medium-energy (E > 0.6 MeV) and high-energy (E > 2.0 MeV) electrons in the radiation belt are discussed. Based on comparing the event with the moderate magnetic storm of January 21–22, 2005, we concluded that favorable conditions for analyzing the interaction between the solar wind and the magnetosphere are formed during a deep minimum of solar activity.     

Semi‐active control of sliding isolated bridges using MR dampers: an experimental and numerical study

Sliding base‐isolation systems used in bridges reduce pier drifts, but at the expense of increased bearing displacements under near‐source pulse‐type earthquakes. It is common practice to incorporate supplemental passive non‐linear dampers into the isolation system to counter increased bearing displacements. Non‐linear passive dampers can certainly reduce bearing displacements, but only with increased isolation level forces and pier drifts. The semi‐active controllable non‐linear dampers, which can vary damping in real time, can reduce bearing displacements without further increase in forces and pier drifts; and hence deserve investigation. In this study performance of such a ‘smart’ sliding isolation system, used in a 1:20 scaled bridge model, employing semi‐active controllable magneto‐rheological (MR) dampers is investigated, analytically and experimentally, under several near‐fault earthquakes. A non‐linear analytical model, which incorporates the non‐linearities of sliding bearings and the MR damper, is developed. A Lyapunov control algorithm for control of the MR damper is developed and implemented in shake table tests. Analytical and shake table test results are compared. It is shown that the smart MR damper reduces bearing displacements further than the passive low‐ and high‐damping cases, while maintaining isolation level forces less than the passive high‐damping case. Copyright © 2005 John Wiley & Sons, Ltd.     

Solar activity and dynamic processes in the atmosphere and world ocean heat content

The scenario of climatic changes in the 20th century has been presented in the scope of the developed model concerning the effect of solar activity on the parameters of the climatic system governing the energy flux, outgoing from the Earth into space in the high-latitude regions. The regularities of changes in the circulation in the atmosphere and ocean are discussed. Specific attention is paid to the causes of a “cold snap” in 1940–1976 in the Northern Hemisphere and the nature of an anomalous increase in the heat content in the Earth climatic system (ocean) in 1969–1980. It has been indicated that these phenomena result from changes in the circulation in the atmosphere and ocean (specifically, a change in the thermohaline circulation in the Northern Atlantic), heat exchange between the ocean and the atmosphere and cryosphere.