Seismotectonic of the Azores-Alboran region

New seismicity and focal-mechanism data from the area of the Azores Islands, in the Mid-Atlantic Ridge, to the Alboran Sea and the southern part of Spain are presented.As a consequence of the different characters in the focal-mechanism solutions and b-values associated, the area has been divided in four different parts, namely, Mid-Atlantic and Terceira Ridge, Azores—Gibraltar fault, Gulf of Cadiz, Alboran Sea and Betica. The last two form the interaction between the Eurasian and African continental plates.The fracture zone is the locus of very large earthquakes with mechanisms showing a predominant right-lateral horizontal motion. Seismic foci in the continental interaction zone are spread over the whole region with mechanisms changing in character from west to east. It is suggested that this may be consequence of the behaviour of the Spanish Peninsula as a partly independent subplate. In the eastern part of the studied zone, the so-called Alboran plate may be considered as a buffer plate.     

新生地震构造带——马边地震构造带最新构造变形样式的初步研究

以雷波地区为例,通过野外地质地貌调查,结合探槽技术以及年代测试结果,获得了有关马边地震构造带最新构造变形样式及其性质的初步认识。研究结果表明：马边地震构造带内的雷波地区存在一条北东东向雷波断裂带,它断错的最新地层时代在40ka左右,属晚更新世活动断裂;在活动性质上,为一条以右旋走滑运动为主的断裂。北北西向玛瑙断裂在第四纪风化壳中存在两次突然位错事件,在剖面上的错距分别为0.5m和>0.7m;最新错动面产状陡立,存在水平左旋位错的构造地貌证据。马边地震构造带上北东东向断裂与北北西断裂不是一种从属关系,而是在现代构造应力场条件下两组呈共轭关系的剪切断裂,它们代表了马边地震构造带最新构造变形样式,具新生性。马边地震构造带的破坏性地震以中强地震为主,具有频度高、成带性差等特点,这符合共轭状构造变形样式可能引起的地震活动特征。马边地震构造带位于青藏高原东缘南部,初步分析表明：一种受重力作用控制的中下地壳塑性流展模型,可以对该地区包括大凉山断裂带、安宁河断裂带以及鲜水河断裂带在内的断裂构造的活动习性做出较合理的解释。伴随着高原内部中下地壳物质持续向外流展,高原边界向外扩张形成新的边界,并表现为一条新生地震构造带。     

Seismotectonic Reactions to the Arc-continent Convergence in Central Philippines

Abstract. High seismic activity in the Philippines originates from tectonic convergence related to surface and subsurface seismotectonic features. Based on earthquake data, the archipelago can be divided into the seismically-active Philippine Mobile Belt and the aseismic North Palawan Block. The latter represents a rifted continental fragment of the Eurasian margin that juxtaposed with the rest of island arc units in central Philippines. Earthquake hypocenter plots on planar and in vertical profiles show that the seismic events are associated with known seismotectonic features. In addition, data suggest that the collision zone between the North Palawan Block and the Philippine Mobile Belt is characterized by a decreased amount of hypocenters at > 100 km depths. Although field evidence favors the presence of a subducted slab or slabs beneath western central Philippines, these are difficult to image using the present seismicity distribution dataset.     

Seismotectonic implications of sand blows in the southern Mississippi Embayment

We explore seismically-induced sand blows from the southern Mississippi Embayment and their implications in resolving the question of near or distal epicentral source region. This was accomplished using aerial photography, field excavations, and cone penetration tests. Our analysis shows that three sand blow fields exhibit a distinct chronology of strong ground motion for the southern embayment: (1) The Ashley County, Arkansas sand blow field, near the Arkansas/Louisiana state border, experienced four Holocene sand venting episodes; (2) to the north, the Desha County field experienced at least three episodes of liquefaction; and (3) the Lincoln–Jefferson Counties field experienced at least one episode. Cone penetration tests (CPT) conducted in and between the sand blow fields suggest that the fields may not be distal liquefaction associated with New Madrid seismic zone earthquakes but rather are likely associated with strong earthquakes on local faults. This conclusion is consistent with the differences in timing of the southern embayment sand venting episodes and those in the New Madrid seismic zone. These results suggest that active tectonism and strong seismicity in intraplate North America may not be localized at isolated weak spots, but rather widespread on fault systems that are favorably oriented for slip in the contemporary stress field.     

灰山港-煤炭坝地震构造环境及动力因子探讨

文章归纳出灰山港－煤炭坝矿震具频度低、强度小、烈度高；系孤立型及主震－余震型；地震活动无明显的规律性可循和无前兆的突发性等特征，进而分析了地震构造环境、地震孕育及发生的动力因子。认为该区处在多个活动在块体交汇及活动断裂夹持区域，是构造应力集聚较高地区，加之，区内存在地壳内花岗岩层和玄武岩层上涌的热能附加应力和人类采掘煤矿工程活动引起的诱发地震的功能，以致灰山港－煤炭坝地区时的有矿震活动。     

Seismotectonic significance of the 29 January 1989 Etne earthquake, SW Norway

The integrated analysis of geological, seismological and field observations with lineament data derived from satellite images allows the identification of a possible seismogenic fault zone for an earthquake which occurred near Etne in southwestern Norway, on 29 February 1989. The hypocentre of the earthquake was located at the mid-crust at a depth of 13.8±0.9 km which is typical of small intraplate earthquakes. The Etne earthquake occurred as a result of normal faulting with a dextral strike-slip component on a NW–SE trending fault. Available geological and lineament data indicate correlation of the inferred seismogenic fault with the NW–SE trending Etne fault zone. An aeromagnetic anomaly related to the Etne fault zone forms a regional feature intersecting both Precambrian basement and allochthonous Caledonian rocks. Based on these associations the occurrence of the Etne event is ascribed to the reactivation of a zone of weakness along the Etne fault zone. Slope-instabilities developed in the superficial deposits during the Etne event demonstrate the existence of potentially hazardous secondary-effects of such earthquakes even in low seismicity areas such as southwestern Norway.     

Seismotectonic regionalization of the Red Sea area and its application to seismic risk analysis

A seismological evaluation of the Red Sea margin is presented in this contribution based on the concept of seismotectonic regionalization. The geology and the tectonic structure are critically reviewed to define regions of homogeneous seismicity in the study area, and available seismicity data are implemented to estimate the seismic parameters of the region. The results of the study are applied to evaluate the seismic hazard of an offshore platform site.     

Seismotectonic Deformation of the Early Medieval Fortress Wall of Derbent (Dagestan)

Doklady Earth Sciences - The results of the latest research on active faults in Southern Dagestan, in the area of Derbent, using the paleoseismological and archeoseismological methods are...     

Seismotectonic studies of the coastal areas of India,Pakistan, Bangladesh,and Burma

Major geotectonic elements that are seismically active in the near-shore areas of the Indian subcontinent are the Mekran fault off the coast of Pakistan, the western part of the Narmada-Son lineament, the West Coast Fault off the west coast of India - a southward extension of the Cambay Rift, the Palghat Gap, the Godavari and Mahanadi grabens, transecting rather at an angle to the eastern coast of India and the Arakan-Yoma arcuate belt of Burma, which is a part of the global Alpine-Himalayan orogenic belt, continuing southwards into the Andaman-Nicobar island complex and the Java-Sumatra trench on the ocean floor of the advancing Indo-Australian Plate.The coastal belt exhibits varied degrees of seismicity from intensely seismic areas, like the Mekran coast off Pakistan, Kutch (India) and the Arakan-Yoma belt of Burma, with earthquake magnitudes of more than 8.0, while the intervening coastal areas of the Peninsular India are moderately seismic to aseismic. The remaining areas, namely, the major part of the coastal belt of Bay of Bengal in India and Bangladesh are broadly aseismic. However, the active Godavari graben and the eastern part of the coast of Bangladesh are frequented by low to moderate magnitude earthquakes. An extension of the active Arakan-Yoma belt in the Bay of Bengal in the form of the Andaman-Nicobar Island complex is highly seismic with a maximum earthquake magnitude of more than 8.0, while the Lakshadweep-Minicoy island complex, situated on the Chagos-Laccadive ridge is moderately seismic. This broad picture of coastal and marginal seismicity is corroborated by the geodynamics of the northern part of the Indo-Australian Plate.Observations along the coastal areas during historic and recent times, however, confirm the absence of significant tsunamis, though very mild tsunami surges have occasionally been observed along the coastal areas of the Bay of Bengal. No active volcanoes are known to exist in the coastal areas.Water reservoirs situated near the marginal areas of the Peninsular Shield exhibit moderate to intense seismic activities, viz. Ukai, Bhatsa, Koyna, Parambikulam, Sholayar, Idduki, and Kinnersani.     

Shallow Structure of the Crust in the Sulu-Dabie Region,China and its Seismotectonic Implication

The P-wave velocity structure in the shallow crust is investigated in and around the Sulu-Dabie region by using seismic reflection data for deep soundings in 48 survey profiles and from rock velocity determinations. The observed velocity distributions show obvious heterogeneities in this region. The low velocity anomalies are observed mainly in the west of the Dabie region and the East Sea regions. The high velocity anomalies emerge in the shallow crust of the Sulu and Dabie orogeny. These high-velocity anomalies can be attributed to the ultra-high pressure metamorphosed (UHPM) rock formed by exhumation motion of mantle materials during the orogeny. The high-velocity anomalies in the different shallow layers beneath the Sulu region are located to the northeast of the Tan-Lu fault. The high-velocity anomalies beneath the Dabie region are located southwest of the Tan-Lu fault. Such a distribution pattern of velocity anomaly zones may reveal historical motion of a left-lateral strike-slip for the Tan-Lu fault, which differs from the result of a right-lateral strike-slip motion regime known from modern seismology, indicating a more complex tectonic motion along the Tan-Lu fault.     

Seismotectonic features of the September 24, 1999 Ahram earthquake in the Zagros,Iran

The September 24, 1999 Ahram Earthquake in southwestern Iran was moderate in energy (M = 5.0–5.5 from different sources) and did not entail significant destruction and casualities. The tectonic position of the source zone, surficial seismic dislocations, and results of macroseismic and seismological study of this seismic event in the junction zone of the Zagros Fold System and the piedmont plain are described in the paper, including data on rejuvenated ancient ruptures exposed in two trenches excavated across the strike of the regional Kazerun-Borazjan Fault. One of the trenches was driven a few months before and the other a year after this seismic event. The conclusion is drawn that new deformations in the Quaternary near-surface sediments observed at the walls of both trenches may be regarded as unusual seismic ruptures of the Ahram earthquake. These ruptures, described as proved primary seismic dislocations of such a moderate seismic event, are a unique phenomenon in the world seismotectonic practice. The localization of the earthquake source zone in the Kazerun-Borazjan Fault Zone with complex kinematics makes it possible to study the internal structure of one of the most important tectonic lines of the Zagros Fold Region.     

Seismotectonic Deformations Related to the 2011 Tohoku Earthquake at Different Stages of the Seismic Cycle,Based on Satellite Geodetic Observations

Doklady Earth Sciences - The data of multiannual satellite geodetic observations before, during, and after the 2011 Tohoku earthquake are interpreted on the basis of the keyboard model of the...     

Seismotectonic evidence of an active normal fault beneath Thessaloniki (Greece)

During 3 weeks in 1985, we operated a dense network of portable seismological stations around the city of Thessaloniki, in Northern Greece, where a destructive earthquake had occurred in 1978. We recorded 282 microearthquakes, with magnitudes ranging between -0.2 to 3.0, and we computed 22 Fault Plane Solutions. The experiment was designed to map the stress pattern west of the 1978 shock, and to study the Asvestohorio fault. Around this fault, located near Thessaloniki, Mercier et al. (1983) observed a few cracks during the 1978 shock. The seismicity shows the same scattered pattern seen through the whole Chalkidiki region. We observe also a dense cluster around Asvestohorio, but this cluster is probably related to explosions in nearby mines. After filtering the data from possible explosions we found evidence of seismic activity. The earthquakes are dipping toward the NE, suggesting that the Asvestohorion fault is active. The Fault Plane Solutions do not help in defining the geometry of the fault but the P and T-axes are consistent with the regional stress pattern.     

Speculations on the nature and cause of mantle heterogeneity

Hotspots and hotspot tracks are on, or start on, preexisting lithospheric features such as fracture zones, transform faults, continental sutures, ridges and former plate boundaries. Volcanism is often associated with these features and with regions of lithospheric extension, thinning, and preexisting thin spots. The lithosphere clearly controls the location of volcanism. The nature of the volcanism and the presence of ‘melting anomalies’ or ‘hotspots’, however, reflect the intrinsic chemical and lithologic heterogeneity of the upper mantle. Melting anomalies—shallow regions of ridges, volcanic chains, flood basalts, radial dike swarms—and continental breakup are frequently attributed to the impingement of deep mantle thermal plumes on the base of the lithosphere. The heat required for volcanism in the plume hypothesis is from the core. Alternatively, mantle fertility and melting point, ponding and focusing, and edge effects, i.e., plate tectonic and near-surface phenomena, may control the volumes and rates of magmatism. The heat required is from the mantle, mainly from internal heating and conduction into recycled fragments. The magnitude of magmatism appears to reflect the fertility, not the absolute temperature, of the asthenosphere. I attribute the chemical heterogeneity of the upper mantle to subduction of young plates, aseismic ridges and seamount chains, and to delamination of the lower continental crust. These heterogeneities eventually warm up past the melting point of eclogite and become buoyant low-velocity diapirs that undergo further adiabatic decompression melting as they encounter thin or spreading regions of the lithosphere. The heat required for the melting of cold subducted and delaminated material is extracted from the essentially infinite heat reservoir of the mantle, not the core. Melting in the upper mantle does not requires the instability of a deep thermal boundary layer or high absolute temperatures. Melts from recycled oceanic crust, and seamounts—and possibly even plateaus—pond beneath the lithosphere, particularly beneath basins and suture zones, with locally thin, weak or young lithosphere. The characteristic scale lengths—150 to 600 km—of variations in bathymetry and magma chemistry, and the variable productivity of volcanic chains, may reflect compositional heterogeneity of the asthenosphere, not the scales of mantle convection or the spacing of hot plumes. High-frequency seismic waves, scattering, coda studies and deep reflection profiles are needed to detect the kind of chemical heterogeneity and small-scale layering predicted from the recycling hypothesis.     

Reflections on the history of western attitudes to nature

This paper explores some of the fundamental ideas which have shaped Western attitudes toward the natural world. Four vital sets of ideas about nature and humanity, still current today, are examined: the relationship of the human race to other forms of life; the study of the interrelationships in the natural world; the transformation of nature by human agency; and subjective, emotional and aesthetic reactions to nature. Most of these ideas, though transformed throughout human history, have their roots in the classical world. Both classical and biblical conceptions were hospitable to an anthropocentric view of the role of human beings with regard to nature. The broader conception of the human race as a custodian of other forms of life has been a powerful ingredient in modern movements for conservation. Since about the middle of the 18th century, there has been increasing concern with the interrelationships in nature, and here two developments can be noted: the persistent idea of man as a geographic agent and the realization that human transformations of nature have provoked unforeseen and often unintended changes.