Contemporary Earthquakes Research Articles

A synoptic view of the natural time distribution and contemporary earthquake hazards in Sumatra, Indonesia

Tectonic plate interactions in Sumatra have caused a range of devastating earthquake events. In this study, we develop an analytical framework, known as earthquake nowcasting (Rundle et al. in Earth and Space Science 3:480–486, 2016. 10.1002/2016EA000185), to assess the current dynamical state of earthquake hazards in Sumatra and adjacent islands from the empirical distribution of natural times, the cumulative counts of “small” events (say, M ≥ 4) between two successive “large” earthquakes (say, M ≥ 6.5). Based on 50 years of instrumental earthquake data, the best fit Weibull distribution assigns earthquake potential score between 29 and 96% to 19 large cities in the study region with the values (%) of Aceh (72), Bengkulu (34), Binjai (81), Jambi (35), Lahat (29), Lampung (45), Lhoksuemawe (54), Medan (75), Mentawai (76), Meulaboh (71), Nias (95), Palembang (80), Padang (74), Pekanbaru (39), Sabang (72), Siantar (82), Sibolga (92), Sinabang (96), and Tanjung Balai (55). These areal-source based nowcast scores, analogous to the tectonic stress buildup since the last major event, essentially provides a unique characterization of the current level of seismic progression of a city through its repetitive cycle of regional earthquakes. Inclusion of dependent events with aftershocks being more common and the concept of natural times are some of the distinctive advantages of the proposed method. The resulting natural time statistics and consequent earthquake potential scores will facilitate seismic risk estimation, multistate decision-making, and community awareness, leading to an efficient seismic risk reduction strategy in the densely populated study region.

Contemporary Earthquake Hazards in the West-Northwest Himalaya: A Statistical Perspective through Natural Times

AbstractHimalayan earthquakes have deep societal and economic impact. In this article, we implement a surrogate method of nowcasting (Rundle et al., 2016) to determine the current state of seismic hazard from large earthquakes in a dozen populous cities from India and Pakistan that belong to the west-northwest part of Himalayan orogeny. For this, we (1) perform statistical inference of natural times, intersperse counts of small-magnitude events between pairs of succeeding large events, based on a set of eight probability distributions; (2) compute earthquake potential score (EPS) of 14 cities from the best-fit cumulative distribution of natural times; and (3) carry out a sensitivity testing of parameters—threshold magnitude and area of city region. Formulation of natural time (Varostos et al., 2005) based on frequency–magnitude power-law statistics essentially avoids the daunting need of seismicity declustering in hazard estimation. A retrospective analysis of natural time counts corresponding to M≥6 events for the Indian cities provides an EPS (%) as New Delhi (56), Chandigarh (86), Dehradun (83), Jammu (99), Ludhiana (89), Moradabad (84), and Shimla (87), whereas the cities in Pakistan observe an EPS (%) as Islamabad (99), Faisalabad (88), Gujranwala (99), Lahore (89), Multan (98), Peshawar (38), and Rawalpindi (99). The estimated nowcast values that range from 38% to as high as 99% lead to a rapid yet useful ranking of cities in terms of their present progression to the regional earthquake cycle of magnitude ≥6.0 events. The analysis inevitably encourages scientists and engineers from governments and industry to join hands for better policymaking toward land-use planning, insurance, and disaster preparation in the west-northwest part of active Himalayan belt.

Influence of anthropogenic landscape modifications and infrastructure on the geological characteristics of liquefaction

Abstract Many large cities worldwide are built on natural and engineered geological materials that are highly susceptible to liquefaction and associated ground failure in earthquakes. Constitutive equations describing relationships between sediment geotechnical characteristics, seismological parameters, and liquefaction susceptibility of natural and engineered sediments are well established. What is less understood is the role of anthropogenic landscape modifications (e.g., river channel modifications, sediment engineering and re-distribution) and infrastructure (e.g., buildings, buried infrastructure such as drainage systems) on the spatial distributions and severity of liquefaction and ground deformation. Here we use stratigraphic studies, ground penetrating radar (GPR), and analyses of high-resolution aerial photographs to evaluate surface and subsurface geological manifestations of recurrent liquefaction in anthropogenically-modified landscapes during the 2010–2011 Canterbury earthquake sequence in New Zealand. Engineered fill layers provided low density, high permeability traps that captured fluidized sediment and promoted the formation of a unique assemblage of liquefaction-induced sediment intrusions that differ from those preserved in proximal natural sediment. Subsurface drainage systems imparted significant influence on the location, size and orientations of liquefaction ejecta features. Sediments adjacent to engineered stream channels experienced large lateral strains that are unlikely to have occurred in the absence of channel modifications. Spatial variations in naturally-formed topography and liquefaction-susceptible sediments exerted strong influence on the characteristics of liquefaction hazards, even in highly engineered environments. Collectively, these observations highlight important interactions between natural and engineered environments that should be carefully considered when interpreting the geologic effects of contemporary earthquakes and / or using prehistoric geological records to forecast future hazards.

Block-like versus distributed crustal deformation around the northeastern Tibetan plateau

It has been debated for decades whether crustal deformation in and around the Tibetan plateau is distributed or block-like. We model crustal deformation in northeastern Tibet using a deformable-block-motion model, in which kinematic parameters of block motion and internal deformation and the associated boundary slip rates are inverted for using GPS velocity data. The F-test is used to screen out station velocity outliers, justify independence of neighboring blocks, and determine the significance of block internal strains through an iteration process. As a result, fifteen blocks are identified, with their boundary faults slipping at rates of 1–10mm/a. Blocks located east and north of the plateau have large sizes (>104km2 in area) in general, with little internal deformation. Six blocks within the plateau, in contrast, are smaller in sizes, with internal strain rates on the order of 1–10nanostrain/a. Five blocks sitting at the northeast borderland of the plateau have small block sizes but no significant internal deformation. Our results show sinistral slip rates of 4.3±1.6 and 4.6±1.8mm/a across the western and eastern segments of the Haiyuan fault, and 10.8±2.3, 4.6±2.6, and 3.8±2.1mm/a across the western, central, and eastern segments of the East Kunlun fault, respectively. The southwestern, central, and northeastern segments of the Longmenshan fault slip right-laterally at rates of 1.7±1.1, 1.1±0.8, and 1.1±0.8mm/a, with shortening rates of 1.1±1.2, 0.4±0.8, and 0.8±1.1mm/a, respectively. We also develop a scheme to convert geodetic strain rate into seismic moment accumulation rate within blocks and at block boundaries, and estimate the two rates as ∼8.40×1018 and ∼2.06×1019N·m/a, respectively. In comparison, the corresponding seismic moment release rates are estimated as ∼6.06×1018 and ∼2.44×1019N·m/a using an contemporary earthquake catalog of 1920–2015. Such results indicate that the seismic moment accumulation and release rates are comparable for the latest 95years when the earthquake catalog is complete for strong to large events. Both geodetic and seismic estimates suggest that a major portion (∼70–80%) of the total seismic moment is accumulated and released at block boundaries, and a minor but still significant portion (∼20–30%) is accumulated and released within blocks.

Seismic Resistance Evaluation of Traditional Ottoman Timber-Frame Hımış Houses: Frame Loadings and Material Tests

Traditional Ottoman timber-frame houses (“ hımış”) form the major part of the cultural heritage structures in Turkey. There are many studies in the literature regarding the seismic performance of hımış houses, which claim that these structures have an inherent seismically resistant property. However, these studies lack a quantitative engineering approach and are based on observations made after contemporary earthquakes. This study presents the results of the seismic resistance evaluation of traditional Ottoman houses, made by means of reverse cyclic frame tests conducted on six yellow pine and two fir frames with and without infill (brick and adobe) or cladding ( bağdadi and şamdolma). The experimental study, which was intended to differentiate the effects of infill materials, frame geometry, and timber type, has revealed that frames with bağdadi cladding and adobe infill resulted in the best and worst structural performances, respectively, while high ductility and good energy dissipation capacity characteristics were determined.

Role of Transverse Tectonics in the Himalayan Collision: Further Evidences from Two Contemporary Earthquakes

Abstract: Two contemporary earthquakes originating in the central Himalayan arc and its foredeep (Sikkim earthquake of 18.09.2011, Mw 6.9, h: 10-60 (?) km and Bihar-Nepal earthquake of 20.08.1988, Mw 6.8, h: 57 km) are commonly associated with transverse lineaments/faults traversing the region. Such lineaments/faults form active seismic blocks defining promontories for the advancing Indian Craton. These actually produce conjugate shear faulting pattern suggestive of pervasive crustal interplay deep inside the mountains. Focal mechanism solutions allow inferring that large part of the current convergence across the central Himalayan arc is accommodated by lateral slip. Similar slip also continues unabated in the densely populated foredeep for distances up to several tens of kilometers south of the Main Boundary Thrust (MBT).

Testing and Seismic Capacity Evaluation of a Typical Traditional Ottoman Timber Frame

In Turkey, as well as in Balkan countries, examples of an extant housing tradition namely hımış, which was formed during Ottoman period, can still be observed. In spite of minor local differences according to geographical locations, these Ottoman hımış houses are distinguished with a number of common architectural and technical peculiarities that is worth to preserve. They have similar timber frame construction system with different infill materials. There are numerous reports claiming that the hımış houses are seismically more resistant than other construction types such as reinforced concrete and/or masonry structures. However, nearly all such reports are based on observations made after historical or contemporary earthquakes and lack quantitative engineering approach. For these reasons, within the framework of an ongoing research project, supported by The Scientific and Technological Research Council of Turkey (TUBITAK), coded 106M499, the seismic resistance of traditional timber frame houses in Turkey was investigated. A number of timber frames were tested in the laboratory under cyclic and reverse lateral loading, with and without infill. The results were reproduced with pertinent analytical work. As a result, it was shown that connections that were traditionally made with the sole use of standard nails were always the location of failure. In this paper, the results obtained for one of these frames is presented together with its capacity curve analysis to see whether strengthening is needed or not from seismic design point of view.

The history of historical earthquake research in Germany

The paper summarizes the history of collecting and evaluating information on earthquakes in Germany. A rich literature mentioning historical and contemporary earthquakes has existed since the 16th century. Early earthquake catalogues began to appear in the middle of the 16th century, some of which report earthquakes in Germany dating back to the 9th century. Modern seismological views were introduced in connection with intense philosophical analysis of the 1755 Lisbon earthquake, which was largely observed in Central Europe. The 19th century was characterized by a tremendous increase in detailed earthquake studies as well as earthquake compilations in the form of catalogues. The most comprehensive non-parametric catalogues were created in the middle of the 20th century, while the first digital parametric catalogues were published in the 1980s. This was also the time when critical studies on the re-interpretation of historical earthquakes began. Only in the 1990s was such analysis made in a systematic manner resulting in numerous publications and the current development of a modern earthquake catalogue.

The Bible, theodicy and Christian responses to historic and contemporary earthquakes and volcanic eruptions

Theodicy is defined as the process of seeking to reconcile the reality of human suffering with the notion of a loving God. It is commonly associated with several models first proposed by Leibniz in the 18th century, though theodicy as an intellectual and religious pursuit is much older, with antecedents stretching back to biblical times. It is argued that within Christian theology ‘divine retribution’ is not only the most prominent theodicy within scripture, but is also the one most frequently adopted historically as the preferred explanation for losses and suffering caused by disasters, including those produced by earthquakes and volcanic eruptions. Contrary to what some historians of the earth sciences have maintained, we argue that in many societies with a Christian ethos there is little evidence to suggest that religious explanations have ceased to be important. The case is made that a model of ‘divine retribution’ is not merely a feature of biblical narratives, Christian history and pre-industrial societies, but also continues to guide the ways in which some, albeit a minority, of Christians interpret disaster losses today. An argument is advanced that other Leibnizian theodicies, especially the ‘best of all possible worlds’ model, are also supported biblically and have been increasingly adopted by Christians to explain disaster losses particularly since the 18th century. In recent decades the nature of theodicy has changed fundamentally. In some cases this has involved the development of theodicies such as the ‘free-will defence’ which have long existed within the Leibnizian canon, but in other instances theologians have moved beyond this tradition to produce what may be termed ‘post-Leibnizian’ models, of which the ‘liberationist’ is the best supported biblically and theologically. Close relationships between ‘liberationist theodicy’ and liberation theology, which is prominent in many economically less developed countries especially in Latin America, are discussed. Finally, the implications of ‘liberationist’ theodicy for Christian social action (i.e. praxis) and hazard planning are noted.

A GIS model for settlement suitability regarding disaster mitigation, a case study in Bolu Turkey

A GIS (Geographic Information Systems) model was developed for Bolu Province in Turkey primarily for earthquake disaster mitigation purposes. The model served as the basis for investigating earthquake disaster vulnerability of existing settlements and identifying areas for new settlements in the Bolu Provincial Center and its counties. The set of criteria investigated in the GIS model was the following: distance from the main fault, ground acceleration, geologic basement type and terrain slope. Based on these criteria, a settlement suitability map was created, which classified the province into low, medium and high settlement suitable areas. This map was then augmented with other criteria for refinement purposes. These included the land use capability classes map of the province, the contemporary land use map derived from satellite images and the historical and contemporary earthquake occurrences within the region. Finally, the road network of the province derived from satellite images was overlaid on the settlement suitability map so that the provincial administrators could leave an evacuation zone of 200 m around the roads. This settlement suitability map is also intended to assist provincial administrators in making plans for reinforcement of existing settlements in low settlement suitable regions and opening new areas for urbanization and industrialization in high settlement suitable regions.

THE SHADOW-ZONE OF LARGE ITALIAN EARTHQUAKES. EARLY JOURNALISTIC SOURCES AND THEIR PERCEPTION OF 17TH-18TH CENTURIES SEISMICITY

From their earliest beginnings in the 16th century, journalists never failed to find earth-quakes interesting. As a result, early journalistic sources offer a huge hoard of original earthquake data, mostly untapped to this day for seismological purposes [Camassi and Castelli, 2003]. In the aftermath of large earthquakes, the journalists of the 17th and 18th centuries tended to react in two ways. Either their interest for seismic news would increase, leading them to hunt for more news of the same kind, or it would focus exclusively on the “big one” to the detriment of lesser contemporary earthquakes. In the first case, it was possible that more earthquakes than usual would be given coverage; but in the second case more earthquakes than usual were likely to be overlooked and shadowed by the larger event. Through a comprehensive cross-check of Italian early journalistic sources, this paper attempts to highlight the “shadow-zones” of some major 17th–18th centuries Italian earthquakes.

Palaeoseismic Events in Karst Terrains along the Northern Bulgarian Black Sea Coast

AbstractThe study of the palaoseismic events in the karst terrains of the Bulgarian Black Sea coast is a very important up‐to‐date problem. The investigated region is one of the highest‐energy regions in Bulgaria with established and recorded catastrophic historic and contemporary earthquakes. The terrain is subjected to the influence not only of its own earthquake foci but also of those in Romania and Russia. The palaeoearthquakes that caused considerable disturbances in the karst terrains along the Northern Bulgarian Black Sea coast have left significant traces. They caused disturbances in the environment and the relief (rearrangement of the surface and ground water karst basins, partially or entirely collapsed caves, deformed caves, oil, gas and salt intrusions and gravitationally formed caves). The ecological consequences in historic and contemporary aspects were catastrophic. The palaeoseismic dislocations were formed as a result of global, regional and local geodynamic events related with the destruction of the Moezian platform and the regional extension of the Black Sea basin. The time of their display and their spatial interrelations were established as a result of complex investigations accompanied by original documents.

Glacio-seismotectonics: ice sheets, crustal deformation and seismicity

The last decade has witnessed a significant growth in our understanding of the past and continuing effects of ice sheets and glaciers on contemporary crustal deformation and seismicity. This growth has been driven largely by the emergence of postglacial rebound models (PGM) constrained by new field observations that incorporate increasingly realistic rheological, mechanical, and glacial parameters. In this paper, we highlight some of these recent field-based investigations and new PGMs, and examine their implications for understanding crustal deformation and seismicity during glaciation and following deglaciation. The emerging glacial rebound models outlined in the paper support the view that both tectonic stresses and glacial rebound stresses are needed to explain the distribution and style of contemporary earthquake activity in former glaciated shields of eastern Canada and Fennoscandia. However, many of these models neglect important parameters, such as topography, lateral variations in lithospheric strength and tectonic strain built up during glaciation. In glaciated mountainous terrains, glacial erosion may directly modulate tectonic deformation by resetting the orogenic topography and thereby providing an additional compensatory uplift mechanism. Such effects are likely to be important both in tectonically active orogens and in the mountainous regions of glaciated shields. In general, the short-term response to ice fluctuations is similar to the Earth's response to fluctuations in water reservoirs with the subsequent increase or decrease in seismicity which depends on the pre-existing stress state. When the ice fluctuations occur on the spatial scale, and magnitude, of the Late Pleistocene glaciation and deglaciation, however, the viscoelastic response of the Earth (especially the mantle) causes significant changes in crustal deformation and earthquake activity that is spatially extensive and temporally complex. The regions of greatest ice thickness and the regions marginal to the Late Pleistocene ice sheets indicate the most dramatic evidence of earthquake faulting. The mantle response to these large ice mass fluctuations and the change in mass between the oceans and land caused, and continues to cause, measureable crustal deformation at hundreds of kilometres from the ice margins. For both tectonically active and cratonic regions, palaeoseismic investigations of Late Pleistocene and Holocene faults are an important tool in evaluating earthquake hazard. The predicted response of the Earth over this time, however, is very dependent on the model assumed. For most regions, far more carefully designed field observations are needed to constrain the existing rheological and ice models.

Macroseismic intensity evaluation with the <<Fuzzy Sets Logic>>

The use of a macroseismic scale often requires subjective choices and judgments which may produce inhomogeneities and biases in the resulting intensities. To get over this problem it would be necessary to formalize the decision process leading to the estimation of the macroseismic intensity but, on historical records, this is often hindered by the poorness and incompleteness of the aLailable information and by the intrinsical ambiguity of the common language. Moreover. all the intensity scales have always been created and updated to be used <<in the field. on contemporary earthquakes and then it may happen tkdt even detailed historical descriptions often do not correspond to the descriptive frameworks of any grade. I11 order to face these problems. we propose in this work a computer method for the evaluation of the macroseismic intensity which makes use of the <<Fuzzy Sets Logic>>T. his approach reproduces the taslts performed by the hurnan brain which. taking advantage of the tolerance of imprecision. is able to handle with information bearing only an approximate relation to the data. This allows to understand and make explicit some passes of the evaluation process that are unconsciously followed by the macroseismic exper

Systematic stress variations in the southern San Joaquin Valley and along the White Wolf fault: Implications for the rupture mechanics of the 1952 Ms 7.8 Kern County earthquake and contemporary seismicity

The southern San Joaquin Valley (SSJV) stress state is characterized by systematic variations in the regional principal stress directions and relative magnitudes, as well as local and possibly temporal variations that appear to be the result of the 1952 Ms 7.8 Kern County earthquake. The regional maximum horizontal principal stress (SHmax) orientation in the San Joaquin Valley systematically rotates from ∼NE‐SW compression along the western margins of the valley to ∼N‐S compression in the SSJV. This ∼N‐S SHmax stress direction in the SSJV is consistent with active development of a ∼E‐W trending structural fabric of fold axes and shallow thrust, and the reverse dip‐slip motion observed during the Kern County earthquake on the south‐southeast dipping White Wolf fault. Contemporary seismicity (30–40 years after the mainshock) clusters in two separate areas along the White Wolf fault: the southwest region where the 1952 earthquake nucleated, and the northeast region near where the earthquake rupture terminated. Earthquakes in the southwest and northeast regions show a diversity of focal mechanisms that include strike‐slip, reverse, oblique, and, to a lesser extent, normal slip. Inversion of earthquake focal mechanisms for in situ stress in the southwest region indicates a strike‐slip/reverse stress regime with S1 oriented approximately perpendicular to the ruptured fault plane implying low frictional strength in the nucleation zone of the 1952 earthquake. Inversion of focal plane mechanisms in the northeast region indicates a strike‐slip stress regime with S2 nearly perpendicular to secondary 1952 rupture planes also implying low frictional strength. These results indicate near‐complete stress drops for fault planes associated with the 1952 earthquake (and some of the contemporary earthquakes), implying fault surfaces which are frictionally weak (i.e., slip planes subparallel to principal stress planes). Based on the observed stress state in the southern San Joaquin Valley, much of the seismicity may be the result of elevated fluid pressures within these active fault zones.

Structural Controls on the Teton Normal Fault, Teton County, Wyoming

The Teton normal fault crops out along the eastern base of the Teton Range and relative motion across this fault has both uplifted the Teton Range and down-dropped Jackson Hole. On surface maps the normal fault appears to lie across older Laramide faults at a high angle, thus suggesting that previous structures had little to do with the position of the normal fault. Therefore, this field study was undertaken to test the following question: have preexisting Laramide or basement structures affected the position and/or geometry of the Teton normal fault? This question becomes important when considering the potential for contemporary earthquakes along the Teton normal fault and understanding the geologic environment of these earthquakes.

Tectonic development of the New Madrid rift complex, Mississippi embayment, North America

Geological and geophysical studies of the New Madrid Seismic Zone have revealed a buried late Precambrian rift beneath the upper Mississippi Embayment area. The rift has influenced the tectonics and geologic history of the area since late Precambrian time and is presently associated with the contemporary earthquake activity of the New Madrid Seismic Zone. The rift formed during late Precambrian to earliest Cambrian time as a result of continental breakup and has been reactivated by compressional or tensional stresses related to plate tectonic interactions. The configuration of the buried rift is interpreted from gravity, magnetic, seismic refraction, seismic reflection and stratigraphic studies. The increased mass of the crust in the rift zone, which is reflected by regional positive gravity anomalies over the upper Mississippi Embayment area, has resulted in periodic subsidence and control of sedimentation and river drainage in this cratonic region since formation of the rift complex. The correlation of the buried rift with contemporary earthquake activity suggests that the earthquakes result from slippage along zones of weakness associated with the ancient rift structures. The slippage is due to reactivation of the structure by the contemporary, nearly E-W regional compressive stress which is the result of plate motions.