Historical Seismic Activity Research Articles

The Dawn of Earthquake Prediction Research in China: A Case Study of Seismic Activity in the Tianshan Mountains

The paper adopts the Unified Earthquake Catalog of China and according to the Chen Lijun's Seismo-geothermcs and its working method, and studies the planar and three-dimensional distribution images, sequential processes, abnormal states in the last two years, the background of historical seismic activity and the influence of seismic cone tectonic environment in the Tianshan Mountains. In this paper, with reference to the author's experience in the global case study of intracrustal strong seismic activity, it is believed that the seismic geothermal anomaly of the Nantianshan seismic sub-seismic cone tectonic can be confirmed without error, so it is speculated that the intracrustal strong seismic activity of M6. 5-7 may occur in Aksu area in the next 1-2 years in the tectonic influence area, which is worthy of high vigilance and close attention. This strong earthquake prediction opinion has been verified by the M7. 1 earthquake in Aksu, Xinjiang on January 23, 2024, which deserves affirmation.

Multifractal features of the seismicity in Tehuantepec Isthmus, southern México

On September 07, 2017 occurred an earthquake of M8.2 whose epicenter was located at Tehuantepec Isthmus, México. According with the seismicity monitored, spatial and temporal changes were observed after the earthquake in comparison with the historical seismic activity in the zone. Concerning with the temporal changes, the rate of earthquakes occurrence increased and, regarding with the spatial distribution, the epicenters displayed a clear clusterization located between the so-named Tehuantepec Transform/Ridge and the Middle America Trench off Chiapas which is recognized as a tectonic collision region. Based on the observed dynamical behavior of the seismic activity in the Tehuantepec Isthmus subduction zone, in this paper we analyze the magnitude catalogue from 2010 to 2020. The aim is to characterize by applying the multifractal detrended fluctuation analysis three periods of activity, the regular seismicity previous to the main shock, the aftershocks and the post aftershock activity. Our findings suggest that each period is characterized by their own multifractality.

Block Kinematics in North China From GPS Measurements

AbstractThe North China Craton (NCC) is an important tectonic element in China, which is characterized by intense seismic activity and complex tectonic setting. Thus quantifying its deformation is essential for studying the tectonic processes and deformation mechanisms in this region. Here we use a combination of dense GPS data sets to analyze the crustal movement and present updated estimates of fault motions based on elastic block models. We uncover spatial variations in deformation patterns, indicating that different mechanisms may dominate the tectonic processes for different parts of the NCC. In the western part, the rifts around the Ordos block manifest strike‐slip and extensional deformation, and the strike‐slip motion is more significant than the extensional component; whereas in the east, the Tanlu fault experiences right‐lateral and shortening slips, consistent with the features from historical seismic activity and regional tectonics. Our analysis indicates that the deformation in the eastern NCC is principally influenced by the Pacific subduction, whereas the deformation in the western NCC is mainly related to the India‐Eurasia collision. Moreover, our estimate of motion along the Tanlu fault supports a relatively long seismic interval of ∼10 ka, comparable to those inferred from recent paleoseismic research on this fault and other slow‐slip faults in the NCC. Our study indicates that the faults in the NCC even with very slow motions may still have the potential to produce strong earthquakes. Thus seismic risks across these slow‐slip faults cannot be ignored and should not be determined solely based on the rate of fault motions.

Hazard and risk assessment for hydraulic fracturing induced seismicity based on the Entropy-Fuzzy-AHP method in Southern Sichuan Basin, China

Significant increases in seismic activity have been recorded since fracturing and extraction began in 2014 in the Changning shale gas development block that is located in the Southern Sichuan Basin, China (SSBC). The primary aim of this paper was to assess the hazard and risk (HR) resulting from the induced seismicity via the Entropy-Fuzzy-AHP (E-FAHP) method. The assessment used for this study was carried out for 2700 grids with a total area of 1089 km2. The results were combined to form a regional earthquake HR map. Firstly, a large amount of raw data was collected and analyzed and six core factors were selected to form the index layers of the model. The b-value and Z-value derived from seismology indicate the level of historical seismic activity, the faults and fractures that reflect the regional structural instability, as well as two human activities that may induce seismicity: hydraulic fracturing and reservoir storage. Secondly, the evaluation criteria and the membership matrix were established, and the objective weight of each grid was obtained by using the Entropy model. Meanwhile, the subjective weight of each factor was calculated under the AHP expert scoring method, and the subjective and objective weight coupling was performed. Thirdly, the fuzzy product of the weight and the membership matrix produced the final evaluation of the grid. Based on different evaluation years, the model was divided into three classifications, among which Classification 1 has a better prediction effect than Classification 2 and can predict the precise occurrence range of new earthquakes. After correcting the combination modes of the initial data of the fracturing platform factors, the Classification 2 prediction effect was greatly improved. This study shows that as long as the key factors are thoroughly understood, the HR of induced earthquake can be predicted and controlled.

Complex causes of landslides after ice sheet retreat: Post-LGM mass movements in the Northern Patagonian Icefield region

Although the dynamics of individual rock-slope failures above recently shrinking glaciers have received increasing study, less is known about the spatial distribution of landslides in paraglacial settings. Here, we present a landslide inventory for large deglaciated area (~100,000 km2) situated within the Last Glacial Maximum (LGM) limits of the Northern Patagonian Icefield (NPI). Using satellite images and the TanDEM-X digital elevation model, we mapped a total of 15,543 landslides, among which 1006 are deep-seated landslides (DSLs) with area ≥0.01 km2. The distribution of DSLs is highly asymmetric in a W-E transect of the NPI region, with pronounced clustering along the semi-arid eastern front of the Patagonian Andes. The most strongly affected domain is volcanic tablelands overlying weak Miocene sedimentary rocks, but DSLs tend to also cluster along recently deglaciated (i.e. since the end of the 19th century) eastern margin of the NPI. Compared with other high mountain regions, alpine valleys of the Patagonian Andes are affected by DSLs only in <1% of their area, an order of magnitude lower than in other reported deglaciated mountains. The modest incidence of DSLs in the Patagonian Andes is due to dominance of hard granitoid rocks and relatively weak historical seismic activity. We conclude that 1) geological conditions control the distribution of DSLs and their types in the NPI region; 2) paraglacial effects play secondary (although locally important) roles in the origin of DSLs; 3) local clusters of large DSLs originate due to specifics of the post-LGM landscape evolution, involving drawdowns of glacial lakes and incision of rivers into the unconsolidated deposits; and 4) increased abundance of landslides above the recently shrinking margin of the NPI results from the repeated Holocene fluctuations of glacier snouts around the Little Ice Age (LIA) glacier limits and the spatial coincidence of glacial debuttressing effects with the presence of active faults.

Geophysical analysis in a Quaternary compressive environment controlling the emplacement of travertine, eastern piedmont of Argentine Precordillera

This work carries out the analysis, through a geophysical (gravity) method, of an area in the eastern Piedmont of Eastern Precordillera, Central Andes of Argentina. Geological evidence shows several neotectonic reverse fault scarps affecting Quaternary alluvial deposits located to the East of the Sierra de Villicum. Topographic features observed in the understudy region suggest an important Holocene historical seismic activity, one of them the 15th January 1944 San Juan earthquake (Mw 7.0), the worst natural disaster in Argentina. Several N–S springs and carbonate deposits (travertine) are found aligned along the traces of these active faults, disappearing abruptly to the north and south, possibly due to a tectonic control. Travertine deposits are located along fault traces and have been traditionally considered to be contemporaneous with active faults. The existence of travertine bodies deposited by springs, and their low preservation potential, has for the understudy region a neotectonic significance. The eastern Piedmont of the Sierra de Villicum is characterized by the ~N–S La Laja west-vergent east-dipping reverse fault and several subparallel faults (e.g., Cantera and Museo faults) that uplift Neogene sedimentary rocks over Quaternary (Late Pleistocene-Holocene) alluvial deposits. Gravity data derived from the global Earth gravity model WGM 1.0 were used in the regional geophysical analysis. The analysis aims to delimit geological structures, which characterized the interest area. Three detailed gravimetric profiles were measured to analyze local anomalies related to the main structures. The gravimetric and geological analysis confirms the existence of north-south faults parallel to La Laja fault related to travertine deposits. On the other hand, a set of southeast-northwest structures that limit and control the travertine bodies both northward and southward are recognized. Employing the gravity method associated with structural analysis, the spatial continuity of these neotectonic structures was defined in those sectors where field evidence is not so clear or blind structures are present. Our study confirms the existence of probable cross strike structures trending NW. We suggest they would represent preexisting crustal fabrics reactivated during the Andean orogeny in the Precordillera province, segmenting this orogen-parallel fold and belt system. One of the main hypotheses is that these fault systems related to basement-involved strike-slip faults perform as control structures in fluid migration during the travertine bodies' emplacement. Thus, our work points to the relevance of travertine location in the analysis of the seismotectonic configuration of a region.

Assessment of geological factors potentially affecting production-induced seismicity in North German gas fields

Recovery of hydrocarbons has triggered seismicity in some Rotliegend reservoirs in the Netherlands and in northern Germany. In Germany, these earthquakes have caused negligible structural damage, but raised public concerns in a region of low historic seismic activity. Production-induced seismicity has been successfully addressed by analytic poroelastic models that explain the development of critically stressed faults with pore fluid pressure depletion inside and around reservoirs. The available analytical approaches fail to account for the mechanical stratigraphy and structural complexities occurring in reality, i.e., reservoirs compartmentalized by faults. The present study aims to increase the quantitative understanding of the geological factors that potentially affect production-induced seismicity in North Germany. In the first part of the paper, a series of 2D finite element models is presented to investigate a parameter space for reservoir depth, reservoir thickness, mechanical reservoir and host rock properties, and compartment geometries typically observed in North German Rotliegend gas fields. The second part addresses the impact of mobile salt layers with variable thickness atop the reservoir on fault stability. The results indicate preferred fault reactivation for steeply dipping faults, large Biot–Willis coefficients, inhomogeneous overburden loads, large reservoir thicknesses, a shallow reservoir position and short distances of the salt layer to the reservoir. In the third part we investigate the effects of fault dip and throw along a fault loaded by three depletion scenarios in a compartmentalized intra-graben setting. Maximum fault loading was obtained for the case that fault throw is half of the reservoir thickness and production is exclusively from the footwall block. The main finding is a preferred reactivation of steeply dipping faults (>60°) caused by the dominant contribution of reservoir compaction to fault loading. Compaction-loading constitutes the main difference to seismicity driven by far field tectonics dominated by horizontal strain, for which faults with dip angles of approximately 60° are predicted favourable for reactivation.

Late Quaternary sackungen in the highest mountains of the Carpathians

Sackungen represents a common mode of deep-seated rock-slope failures in alpine landscapes, but proof of their temporal and causal relationship to extrinsic factors such as climatic changes, glacier retreat or seismic activity remains elusive. Based on the terrestrial cosmogenic nuclide (TCN) dating of 18 sackung scarps supported by one radiocarbon-dated scarp, we reconstructed the post-glacial chronology of sackungen in the Tatra Mts. (central Europe, Slovakia and Poland), the highest part of the Carpathians. The obtained ages (∼15.7–4.3 ka) indicate that sackungen post-date the regional LGM and some of them originated soon after the glacier withdrawal from adjacent valleys. Furthermore, systematic decrease of scarp ages with their increasing altitude suggests a direct link between sackung origin and post-LGM glacier thinning. However, substantial lag (>5 ka) of some sackungen in respect to glacier retreat implies complex relationships between sackung onset and deglaciation where retreat of glaciers acted predominantly as a preparatory, not a triggering factor during the genesis of these slope deformations. They originated either as a consequence of stress relaxation within the rock mass lasting several ka or alternatively could be triggered by climatic processes or seismicity. Indeed, a significant part of sackung activity took place during predominantly warmer and more humid periods, with some dates coinciding with the Bølling–Allerød chronozone, but especially with the onset of the Holocene and the Holocene Climatic Optimum. Earthquake triggering is less probable, as the Tatra Mts. lack significant modern and historic seismic activity and there is no geomorphic evidence of fault offsets on the Late Quaternary landforms. In concert with other recent studies, we propose that large rock slope failures in high mountains seldom react immediately to glacier withdrawal, but could display temporal delay lasting up to several millennia.

Correlating damage condition with historical seismic activity in underground sepulchral monuments of Cyprus

Severe and repeated earthquakes devastated Cyprus in antiquity, causing in many cases the abandonment of entire settlement sites. Yet, information regarding the level of seismic activity of historical seismicity in Cyprus is very limited and does not provide the evidence to arrive at reliable conclusions relative to hazard damage parameters such as the severity or occurrence frequency of a seismic event. Thereafter, the level of risk in which these monuments are exposed is unclear leading to an increased uncertainty regarding their safeguarding from future events.The paper aims at investigating the correlation between damage observed in underground ancient tombs and the historical seismic activity at the area based on in situ observations and expert opinion analysis. In addition, the paper aims to simulate the current state of the tomb's structure, and predict, through a seismic scenario, the propagation of damage from future large earthquake events. Underground monuments are chosen since, due to the nature of the seismic force, they are further “protected” and capable of surviving strong ground motions as they follow the displacement of the soil surrounding them. Typical examples of such structures in Cyprus are the hypogea in the necropolis of the “Tombs of the Kings”, located in Paphos area. Some of these monuments exhibit severe cracking of the rock-cut stone walls and evidence of collapse of vertical resisting members of skeleton structure. Paphos area is the most active seismic region in Cyprus based on the historical catalogue of events with evidence of a number of destructive earthquakes.The framework presented herein utilizes information regarding the current geometry of these structures as documented from topographical surveys, their depth, area of opening, size of resisting members along with information regarding the geotechnical conditions at the site to arrive at estimates of the displacement demand under various seismic scenarios. The predicted shear strain levels on the walls are compared with the strain capacity under tension of the soil material to identify the possibility of propagation of cracking of the walls based on a specific seismic scenario.

Tectonic controls upon Kaveri River drainage, cratonic Peninsular India: Inferences from longitudinal profiles, morphotectonic indices, hanging valleys and fluvial records

The Indian Peninsula is generally considered as a tectonically stable region, where ancient rocks, rivers and land surfaces predominate. In some parts of this ancient landscape, however, the role of tectonic landsculpting is strongly indicated by the presence of youthful topography and historical seismic activity. The present study is primarily focused on the middle domain of the Kaveri River, which displays such youthful features. The tectonic controls on this cratonic river were evaluated on the basis of the investigations of the longitudinal profiles, morphotectonic indices of active tectonics, and fluvial records. The presence of steep channel gradients, prominent knickpoints, hanging valleys, narrow bedrock gorges, and channel-in-channel morphology imply rapid erosion rates in the middle domain of the basin in response to active deformation, particularly in the reach defined by two major active faults — the Kollegal–Sivasamudram Fault and the Mekedatu Fault. Further, considering the remarkably low modern and long-term denudation rates and OSL ages of the alluvial deposits (30–40ka), the tectonically-driven rejuvenation does not appear to be geologically recent as postulated by earlier workers.

Neotectonics of mainland Portugal: state of the art and future perspectives

This paper presents a synthesis of the neotectonic studies performed in mainland Portugal that address the “recent” (post Piacenzian, ~3 Ma) tectonic evolution of the Portuguese territory as part of the West Iberian continental margin, specifically in regard to regional seismic hazard evaluation. The interaction of the Iberian microplate with the Nubia plate is identified as the source for the regional neotectonic deformations, which occur at relatively low rates in spite of significant historical seismic activity. In this context of low strain rates expressed by the presence of slow slip rate active faults, it is important to acquire paleoseismic data on the major seismogenic structures to characterize the large earthquakes that they generated in the past, because average recurrence intervals are much longer than the time span covered by the regional historical and instrumental period.

Seismicity in the North-West Frontier Province at the Indian-Eurasian Plate Convergence

In the last decade a number of large earthquakes have devastated the Asian continental region, including the 1998 MW 6.6 Afghanistan-Tajikistan, 1999 MW 7.6 Chi-Chi, 2001 MW 7.6 Gujarat, 2002 MW 6.1 Hindukush, 2004 MW 9.0 Sumatra-Andaman, 2005 MW 7.6 Kashmir, 2006 MW 6.3 Yogyakarta, and 2008 MW 7.9 Sichuan. Of these, the 1998 Afghanistan-Tajikistan, the 2002 Hindukush, and the 2005 Kashmir nucleated in the northwest region of Indian and Eurasian plate convergence. The earliest accounts of devastating earthquakes in this seismically vulnerable terrain can be traced back to the 8th century (Ambraseys and Bilham 2003). Recently, researchers have used chronological records of events, listed in earthquake catalogs, for statistical assessment of the seismicity in terms of frequency magnitude distributions, spatiotemporal behaviors, and maximum earthquake prognosis ( e.g. , Faenza and Pierdominici 2007; Thingbaijam et al. 2008; Thingbaijam and Nath 2008). The spatial seismicity patterns can be employed for classification of possible areal seismic source zones in the underlying seismotectonic framework of the region. Seismicity of a region encompasses the ongoing earthquake processes and long-term historical seismic activity as well as expectations for the occurrence of future large/great earthquakes. In the present work, we first compile a homogeneous earthquake catalog by converting different magnitude scales to a single scale; in this case, MW . Then we use this catalog to quantify seismicity patterns and to delineate broad seismic source zones and the potential maximum earthquakes in each zone. The quantification of the observed seismicity is achieved through the spatial distribution of b -value and correlation fractal dimension of the epicenters, DC . The tectonic framework of the study region extends from the Herat fault system on the west to northwest Himalaya on the east while touching the offshore boundary …

Present-day stresses, seismicity and Neogene-to-Recent tectonics of Australia's ‘passive’ margins: intraplate deformation controlled by plate boundary forces

Abstract Neogene-to-Recent deformation is widespread on and adjacent to Australia's ‘passive’ margins. Elevated historical seismic activity and relatively high levels of Neogene-to-Recent tectonic activity are recognized in the Flinders and Mount Lofty Ranges, the SE Australian Passive Margin, SW Western Australia and the North West Shelf. In all cases the orientation of palaeostresses inferred from Neogene-to-Recent structures is consistent with independent determinations of the orientation of the present-day stress field. Present-day stress orientations (and neotectonic palaeostress trends) vary across the Australian continent. Plate-scale stress modelling that incorporates the complex nature of the convergent plate boundary of the Indo-Australian Plate (with segments of continent–continent collision, continent–arc collision and subduction) indicates that present-day stress orientations in the Australian continent are consistent with a first-order control by plate-boundary forces. The consistency between the present-day, plate-boundary-sourced stress orientations and the record of deformation deduced from neotectonic structures implicates plate boundary forces in the ongoing intraplate deformation of the Australian continent. Deformation rates inferred from seismicity and neotectonics (as high as 10 −16 s −1 ) are faster than seismic strain rates in many other ‘stable’ intraplate regions, suggestive of unusually high stress levels imposed on the Australian intraplate environment from plate boundary interactions many thousands of kilometres distant. The spatial overlap of neotectonic structures and zones of concentrated historical seismicity with ancient fault zones and/or regions of enhanced crustal heat flow indicates that patterns of active deformation in Australia are in part, governed, by prior tectonic structuring and are also related to structural and thermal weakening of continental crust. Neogene-to-Recent intraplate deformation within the Australian continent has had profound and under-recognized effects on hydrocarbon occurrence, both by amplifying some hydrocarbon-hosting structures and by inducing leakage from pre-existing traps due to fault reactivation or tilting.

Historical Seismic Activity in the Central United States

The expected recurrence of the 1811-1812 New Madrid sequence about every 500 years (Tuttle et al., 2002) dominates the U.S. Geological Survey (USGS) estimates of seismic hazard over much of the central United States (CUS) (Harmsen et al., 1999; Frankel et al., 2000, 2002). While earthquakes in the New Madrid seismic zone (NMSZ) apparently dominated CUS seismicity in the first two decades of the 19th century, more moment magnitude M 5.0 and larger earthquakes have occurred in the Illinois basin in southern Illinois and Indiana in the past 150 years than in the NMSZ (Bakun and Hopper, 2004a). Paleoseismic studies ( e.g., Munson et al. , 1997) have shown, moreover, that large Holocene earthquakes have occurred in the Illinois basin where 5.0≤ M ≤6.0 historical earthquakes have occurred. M ≥ 5.0 historical earthquakes have also occurred in Kansas, Kentucky, Nebraska, and Oklahoma. Thus, a consistent evaluation of historical seismic activity occurring throughout the CUS is important in estimating the seismic hazard. Bakun et al. (2003) developed a model specifically designed to estimate the location and M for historical earthquakes in eastern North America (ENA) and analyzed the 5 January 1843 and 31 October 1895 M 6 CUS earthquakes. Bakun and Hopper (2004b) used this model to estimate the location and M for the three largest events in the 1811-1812 NMSZ earthquake sequence. Bakun et al. 's (2003) model can be used to analyze historical CUS earthquakes with only a few intensity assignments and includes empirical site corrections to account for anomalous site effects, such as the enhanced shaking effects in 1811-1812 in communities built on weak ground along waterways (Hough et al., 2000). Bakun and Hopper (2004a) applied Bakun et al. 's (2003) model to M < 6 historical CUS earthquakes and compiled a catalog of historical seismicity wherein …

Reassessment of the historical seismic activity with major impact on S. Miguel Island (Azores)

Abstract. On account of its tectonic setting, both seismic and volcanic events are frequent in the Azores archipelago. During the historical period earthquakes and seismic swarms of tectonic and/or volcanic origin have struck S. Miguel Island causing a significant number of casualties and severe damages. The information present in historical records made possible a new macroseismic analysis of these major events using the European Macroseismic Scale-1998 (EMS-98). Among the strongest earthquakes of tectonic origin that affected S. Miguel Island, six events were selected for this study. The isoseismal maps drawn for these events enabled the identification of areas characterized by anomalous values of seismic intensity, either positive or negative, to constrain epicentre locations and to identify some new seismogenic areas. Regarding seismic activity associated with volcanic phenomena six cases were also selected. For each of the studied cases cumulative intensity values were assessed for each locality. The distribution of local intensity values shows that the effects are not homogeneous within a certain distance from the eruptive centre, the area of major impacts relates with the eruptive style and damages equivalent to high intensities may occur in Furnas and Sete Cidades calderas. Combining all the historical macroseismic data, a maximum intensity map was produced for S. Miguel Island.

Rapid coastal geomorphic change in the River Murray Estuary of Australia

Abstract The River Murray Estuary, a Ramsar Wetland Site, has experienced considerable rapid coastal change during the Quaternary. The interplay of aeolian processes, river flows, tidal oscillations, wave action and variations in relative sea-level due to global sea-level changes and land subsidence, provides the energy for the ongoing dynamism, often accelerated by human impacts. The estuary is the terminus of the Murray-Darling catchment, which covers 1.073 million km 2 of the Australian continent. Terminal Lakes Alexandrina, Albert and the Coorong Lagoon are Holocene features, occupying tectonically subsiding Quaternary interdune areas. They formed in response to eustatic sea-level rise following the Last Glacial Maximum (ca. 20 ka). The last interglacial shoreline (125,000 yr BP) parallels the modern shoreline several kilometres inland. Dislocation of the last interglacial shoreline demonstrates ongoing tectonic subsidence, as does historical seismic activity. The northern half of Hindmarsh Island formed during last interglacial times when it was the sink for dominant longshore transport from the southeast, which pushed the River Murray westward, partly explaining the large bend in the River Murray at Goolwa. The modern coastal barriers of Sir Richard Peninsula and Younghusband Peninsula formed from 7000 yr ago, following glacier melt and sea-level rise. Subsequently, the barriers have migrated landward, sporadically exposing lagoonal sediments on the ocean beaches. Differential loading of the soft lagoonal sediments by advancing dunes, possibly in conjunction with seismic events, has deformed and elevated them to up to 10 m above present sea-level (APSL). During the mid-Holocene an extensive sand flat, with associated dunes, formed immediately inland of the coastal barrier. At least six generations of Late Pleistocene dune systems occur in the region. For example, during last glacial times the climate was drier, colder and windier than at present and a system of parallel, west–east trending, yellow–red desert dunes developed around the lakes. Aeolian processes remain important with occasionally up to 5000 tonnes of sand being in motion along 10 km of the modern shoreline. During mouth migration, dunes up to 2 m high have been formed and vegetated in 12 months, directly inland from the mouth, and replicating the formation of older dunes on Hindmarsh Island. Elsewhere sand blown directly from the barrier system infills channels. Barrage construction on the beach facies of the last interglacial shoreline transformed the estuary into freshwater lakes with permanently raised water levels and reduced the tidal prism by 90%. Increased deposition, upstream and downstream, accompanied barrage construction, as have accelerated lakeshore erosion and the growth and consolidation of the flood tidal delta (Bird Island). These human accelerated changes provide rapidly formed analogues of older Quaternary features, and aid their interpretation. The shape and location of the Murray Mouth is constantly changing, migrating over 1.6 km since the 1830s. Migrations of up to 6 km over the past 3000 yr have influenced sedimentation on the landward shore of the back-barrier lagoonal system.

Geodetic investigation of the 13 May 1995 Kozani‐Grevena (Greece) Earthquake

The Ms=6.6 13 May 1995 Kozani‐Grevena earthquake struck a region of low historical seismic activity which includes a 10‐year‐old triangulation network in northern Greece. After the earthquake, monuments from this network were occupied with GPS to measure co‐seismic displacements. Inversion of the co‐seismic displacement field to yield a source mechanism is achieved by use of a hybrid simplex‐Monte‐Carlo method which requires no a priori constraints. The model focal mechanism agrees well with the global CMT solution and locally observed aftershocks, but implies a significantly higher scalar moment than do seismological or SAR interferometry studies, and has a longer fault length than the model based on SAR interferometry.

The Kozani-Grevena (Greece) Earthquake of May 13, 1995, Ms = 6.6. Preliminary Results of a Field Multidisciplinary Survey

INTRODUCTION At 08:47 on May 13, 1995, an Ms 6.6 earthquake occurred in Northern Greece and severely damaged the region around the cities of Kozani and Grevena and neighboring villages. This earthquake is the largest for the last decade in Greece, a country which experiences the highest seismicity in western Europe. The epicenter is located in a region of very low historical seismic activity (Figure 1). The coordinates of the main shock of Kozani are 40°09.6′N and 21°40.2′E and the depth is about 8 km. The ISC seismicity catalog does not mention a single earthquake of magnitude greater than 5 within an area 100 km around, and the last destructive earthquake that affected this region occurred during February 896 and destroyed the city of Veria (Papazachos and Papazachou, 1989). This is very quiet in comparison to the other regions of the Aegean domain which, as a whole, exhibit a total...

Spatial migration and compositional changes of Miocene‐Quaternary magmatism in the Western Grand Canyon

Lithospheric extension appears to be responsible for erosional and tectonic evolution of the western margin of the Colorado Plateau. Late Cenozoic (20 Ma to 10,000 years) basaltic flows, scoria cones, necks, dikes, and sills exposed in the Western Grand Canyon region offer a unique opportunity to place age constraints on the landscape evolution. New K‐Ar ages show that these basaltic rocks become progressively younger to the northeast from the Hualapai and Shivwits Plateaus onto the Uinkaret Plateau, a distance of about 100 km. Magmatism appears to have migrated at a rate of about 0.45 cm/yr until sometime between 13.5 and 9.2 Ma, when the rate changed to about 1.15 cm/yr. Recent regional geologic mapping indicates that extensional faulting, with ubiquitous downdrop to the west, accompanied this magmatism; the Hurricane Fault offsets lavas as young as 0.29 Ma. Young fault scarps in sedimentary rocks, and historic seismic activity along these faults, indicate that the region is still undergoing faulting. The basalts form three relatively distinct groups based on their age, chemistry, and geographic distribution: (1) 20–11 Ma, (2) 11–4.5 Ma, and (3) ≤4.5 Ma. The older basalts (&gt;11 Ma) are petrographically and compositionally distinct from younger basalts; their olivine and augite are more Mg rich with lower TiO2 and higher Ni, Cr, and incompatible element contents. Group 1 basalts have more radiogenic Sr and less radiogenic Nd isotopic compositions than younger group 2 and 3 basalts. Overall, present‐day Sr isotopic compositions range from 0.70344 to 0.70505, 143Nd/144Nd from 0.51291 to 0.51227 (εNd = +5.4 to −7.1), and 206Pb/204Pb from 17.951 to 19.091. Group 1 basalts were probably derived from asthenospheric mantle melts that underwent crustal contamination. These basalts appear to have been generated originally from more primitive melts than groups 2 and 3, which were probably also derived from asthenospheric mantle‐derived magmas but underwent only minor crustal contaminations. Group 2 basalts appear to be transitional between groups 1 and 3. The intervals 13–9 Ma and 4.6–4.3 Ma temporally separate the three chemically distinct groups of basalts in the Western Grand Canyon. These periods correspond closely with major Miocene and Pliocene plate reorganizations in the western United States at about 12.5–10 Ma and 3.9–3.4 Ma. These changes in plate motion were reflected in changes in the rate of magmatism migration in the Western Grand Canyon. Recent movements on the Hurricane and Toroweap Faults appear directly related to the &lt;4.5 Ma volcanism and are probably a result of recent plate reorganization.

Palaeomagnetic study of block rotations in the Niksar overlap region of the North Anatolian Fault Zone, central Turkey

This palaeomagnetic study investigates crustal deformation within, and adjacent to, the Niksar overlap area of the North Anatolian Fault Zone (NAFZ) in central-east Turkey. The studied rock formations comprise: (1) red limestones of Late Cretaceous age (3 sites); (2) mafic lavas of Eocene age on the north side (13 sites) and south side (9 sites) of the NAFZ; and (3) volcanic rocks of Pliocene-Quaternary age from the Niksar pull-apart basin within the NAFZ (8 sites). Comparisons with reference palaeofield directions computed from apparent polar wander paths of the Eurasian and Afro-Arabian plates identify two scales of regional and local tectonic rotation: 1. (1) A pre-tilting remanence in the Eocene volcanic rocks south of the NAFZ ( D I = 144.1 −47.5° , β 95 = 7.6°) is interpreted to reflect counterclockwise rotation by 30–40° from the reference palaeofields. Contemporaneous volcanic rocks from the north side of the NAFZ have the same reverse polarity recorded in pre-tilting magnetisations. The remanence is also rotated counterclockwise ( D I = 152.4 −42.5° , α 95 = 11.3°), but by about 8° less than the volcanics on the south side of the NAFZ. Hence similar amounts of rotation are observed on both sides of the NAFZ and are interpreted to reflect motions during the pre-Middle Miocene collisional history in this sector of the Pontides. No distributed clockwise rotations anticipated from subsequent dextral motion along the NAFZ intracontinental transform are observed. The slightly larger anticlockwise rotation found on the south side of the NAFZ probably records relative rotation of en-echelon wedges by continental escape during post-Middle Miocene strike slip along the transform. 2. (2) Within the narrow zone of intense deformation along the NAFZ, Cretaceous limestones appear to be rotated clockwise by dextral strike-slip motion whilst Plio-Quaternary lavas within a fault-bounded block in the overlap region associated with the Niksar pull-apart basin, have magnetisations consistently directed 240–270°E. Magnetic inclinations are not diagnostic of polarity but both polarity solutions identify rapid clockwise rotation at rates in excess of 50°/m.y. A normal polarity solution is favoured and implies that a block (ca. 5 km across) has undergone a strike-slip displacement of around 12 km within the NAFZ during the last polarity chron. Cretaceous-Eocene palaeolatitudes are closer to those predicted from Eurasia than Afro-Arabia, but a study of older rocks is required to resolve affinities of this sector of the Anatolian block. Theoretical models of crustal deformation across intracontinental transforms obeying power-law behaviour and treating the lithosphere as a viscous medium predict that distributed clockwise rotations should be observed about as broad across the NAFZ. These rotations are not observed. Instead intense clockwise rotation is confined to a narrow zone close to the major fault break. The concentration of historic seismic activity here also implies that the bulk of the dextral motion between the Eurasian Plate and the Anatolian block is accommodated by slip along faults close and parallel to the main trace of the NAFZ.