Kinematics of the eastern part of the North Anatolian Fault Zone

The North Anatolian Fault Zone (NAFZ), which marks the boundary between Anatolia and the Eurasian plate, is one of the world's most seismically active structures. Although the eastern part of NAFZ has high seismic hazard, there is a lack of geodetic information about the present tectonics of this region. Even though many scientists would like to study this area, geographical and logistical problems make performing scientific research difficult. In order to investigate contemporary neotectonic deformation on the eastern NAFZ and in its neighborhood, a relatively dense Global Positioning System (GPS) monitoring network was established in 2003. Geodetic observations were performed in three GPS campaigns in an area of 350 km × 200 km with 12-month intervals. In addition, 14 new GPS stations were measured far from the deforming area. Since this region includes the intersection of the NAFZ and the East Anatolian Fault Zone (EAFZ), deformation is complex and estimating seismic hazard is difficult. One important segment is the Yedisu segment and it has not broken since the 1784 earthquake. After the 1992 Erzincan and 2003 Pulumur earthquakes, the Coulomb stress loading on the Yedisu segment of the NAFZ has increased significantly, emphasizing the need to monitor this region. We computed the horizontal velocity field with respect to Eurasia and strain rates field as well. GPS-derived velocities relative to Eurasia are in the range of 16–24 mm/year, which are consistent with the regional tectonics. The principal strain rates were derived from the velocity field. Results show that strain is accumulating between the NAFZ and EAFZ along small secondary fault branches such as the Ovacik Fault (OF).     

Crustal velocity structure in the southern edge of the Central Alborz (Iran)

Inversion of local earthquake travel times and joint inversion of receiver functions and Rayleigh wave group velocity measurements were used to derive a simple model for the velocity crustal structure beneath the southern edge of the Central Alborz (Iran), including the seismically active area around the megacity of Tehran. The P and S travel times from 115 well-located earthquakes recorded by a dense local seismic network, operated from June to November 2006, were inverted to determine a 1D velocity model of the upper crust. The limited range of earthquake depths (between 2 km and 26 km) prevents us determining any velocity interfaces deeper than 25 km. The velocity of the lower crust and the depth of the Moho were found by joint inversion of receiver functions and Rayleigh wave group velocity data. The resulting P-wave velocity model comprises an upper crust with 3 km and 4 km thick sedimentary layers with P wave velocities (V_p) of ～5.4 and ～5.8 km s^?1, respectively, above 9 km and 8 km thick layers of upper crystalline crust (V_p ～6.1 and ～6.25 km s^?1 respectively). The lower crystalline crust is ～34 km thick (V_p ～ 6.40 km s^?1). The total crustal thickness beneath this part of the Central Alborz is 58 ± 2 km.     

Crustal deformation before the 2008 Wenchuan MS8.0 earthquake studied using GPS data

We used GPS velocities from approximately 700 stations in western China to study the crustal deformation before the Wenchuan M_S8.0 earthquake. The processing methods included analyses of the strain rate field, inversion of fault locking and the GPS velocity profiles. The GPS strain rate in the E-W direction in the Qinghai-Tibet block shows that extensional deformation was dominant in the western region of the block (west of 92.5° E), while compressive deformation predominated in the eastern region of the block (from 92.5° E to 100° E). On a regional scale, the hypocentral region of the Wenchuan earthquake was located at the edge of an intense compression deformation zone of about 1.9 × 10⁻⁸/a in an east-west direction. The characteristic deformation in the seismogenic fault was compressive with a dextral component. The compression deformation rate was greater in the fault's western region than in its eastern region, and the strain accumulation was very slow on the fault scale. The results of a fault locking inversion show that the locking fraction and slip deficit was greater in the middle-northern section of the seismogenic fault than in the southern section. The GPS velocity profile before the Wenchuan earthquake shows that the compression deformation was smaller than the dextral deformation, which is asymmetrical with respect to the distribution of co-seismic displacement. These deformation characteristics should provide some clues to the Wenchuan earthquake which occurred in the later period of the earthquake cycle.     

Elasticity of antigorite,seismic detection of serpentinites,and anisotropy in subduction zones

Serpentinization of the mantle wedge is an important process that influences the seismic and mechanical properties in subduction zones. Seismic detection of serpentines relies on the knowledge of elastic properties of serpentinites, which thus far has not been possible in the absence of single-crystal elastic properties of antigorite. The elastic constants of antigorite, the dominant serpentine at high-pressure in subduction zones, were measured using Brillouin spectroscopy under ambient conditions. In addition, antigorite lattice preferred orientations (LPO) were determined using an electron back-scattering diffraction (EBSD) technique. Isotropic aggregate velocities are significantly lower than those of peridotites to allow seismic detection of serpentinites from tomography. The isotropic V_P/V_S ratio is 1.76 in the Voigt–Reuss–Hill average, not very different from that of 1.73 in peridotite, but may vary between 1.70 and 1.86 between the Voigt and Reuss bonds. Antigorite and deformed serpentinites have a very high seismic anisotropy and remarkably low velocities along particular directions. V_P varies between 8.9 km s^? 1 and 5.6 km s^? 1 (46% anisotropy), and 8.3 km s^? 1 and 5.8 km s^? 1 (37%), and V_S between 5.1 km s^? 1 and 2.5 km s^? 1 (66%), and 4.7 km s^? 1 and 2.9 km s^? 1 (50%) for the single-crystal and aggregate, respectively. The V_P/V_S ratio and shear wave splitting also vary with orientation between 1.2 and 3.4, and 1.3 and 2.8 for the single-crystal and aggregate, respectively. Thus deformed serpentinites can present seismic velocities similar to peridotites for wave propagation parallel to the foliation or lower than crustal rocks for wave propagation perpendicular to the foliation. These properties can be used to detect serpentinite, quantify the amount of serpentinization, and to discuss relationships between seismic anisotropy and deformation in the mantle wedge. Regions of high V_P/V_S ratios and extremely low velocities in the mantle wedge of subduction zones (down to about 6 and 3 km.s^?1 for V_P and V_S, respectively) are difficult to explain without strong preferred orientation of serpentine. Local variations of anisotropy may result from kilometer-scale folding of serpentinites. Shear wave splittings up to 1–1.5 s can be explained with moderately thick (10–20 km) serpentinite bodies.     

Three-dimensional numerical thermal and rheological modelling in the central Fennoscandian Shield

A three-dimensional model for the central Fennoscandian Shield was constructed for analysing the thermal, the rheological and the structural conditions in the lithosphere. The mesh covers a rectangular area in the southern Finland with horizontal dimensions of 500 km × 400 km and a depth extent of 100 km. Structural boundaries are derived from the several deep seismic soundings carried out in the area. Constructed model is first used in the calculation of the thermal and the rheological models and secondly in analysing the stress and the deformational conditions with the obtained rheology. Thermal and structural models are solved with the finite element method. The calculated surface HFD is between 40 and 48 mW m⁻² in the Proterozoic southern part and below 40 mW m⁻² in the older and northern Archaean part of the model. The calculated rheological strength shows a layered structure with two individual rheologically weak layers in the crust and strong layer in the upper part of the lower crust. The minimum brittle–ductile transition (BDT) depth is around 10 km in the southern part of the model while in the north and north-eastern parts the BDT depth is around 45–50 km. Comparison with the focal depth data shows that as most of the earthquakes occur no deeper than the depth of 10 km are they located in the brittle regime. Resulting stress conditions and possible regions of deformation after the model is subjected to pressure of 50 MPa reveals that the stress field is quite uniformly distributed in different crustal layers and that the elastic parameters control more the state of the stress than the applied rheological structure. In the upper crust, the stress intensity has values between 42 and 45 MPa whereas in the middle crust the values are around 50 MPa. Comparison of the 3-D model with earlier 2-D models shows that some differences in the results are to be expected.     

The Himalayan foreland basin crust and upper mantle

Modeling of multimode surface wave group velocity dispersion data sampling the eastern and the western Ganga basins, reveals a three layer crust with an average V_s of 3.7 km s^?1, draped by ～2.5 km foreland sediments. The Moho is at a depth of 43 ± 2 km and 41 ± 2 km beneath the eastern and the western Ganga basins respectively. Crustal V_p/V_s shows a felsic upper and middle crust beneath the eastern Ganga basin (1.70) compared to a more mafic western Ganga basin crust (1.77). Due to higher radiogenic heat production in felsic than mafic rocks, a lateral thermal heterogeneity will be present in the foreland basin crust. This heterogeneity had been previously observed in the north Indian Shield immediately south of the foreland basin and must also continue northward below the Himalaya. The high heat producing felsic crust, underthrust below the Himalayas could be an important cause for melting of midcrustal rocks and emplacement of leucogranites. This is a plausible explanation for abundance of leucogranites in the east-central Himalaya compared to the west. The uppermost mantle V_s is also significantly lower beneath the eastern Ganga basin (4.30 km s^?1) compared to the west (4.44 km s^?1).     

GPS-derived velocity field of the Iznik-Mekece segment of the North Anatolian Fault Zone

Space-based tectonic studies on the western part of the North Anatolian Fault Zone (NAFZ) have been conducted over two decades. After the August 17, 1999, Izmit earthquake (M_w = 7.4), this region attracted greater scientific interest, and the collected data became more valuable. The Geodesy Department of the Kandilli Observatory and Earthquake Research Institute (KOERI) at Bogazici University established three micro-geodetic networks to the east of Akyazi, east of Iznik, and west of Lake Sapanca in the eastern part of the Marmara region; GPS data have been continually collected at these locations since 1994. The NAFZ branches out in the western part of the Marmara region and extends up to the Aegean Sea. Segments of the fault passing through the Marmara Sea are considered active, and this has increased concern regarding imminent earthquakes. Conventional geodetic measurements made between 1990 and 1994 are not sufficient for monitoring small movements. However, GPS has played a very important role in detecting such deformations in the area after 1994. The Iznik network, with 10 points, is bilaterally located on the Iznik-Mekece fault. Six years of GPS data for 2004–2010 collected for the monitoring of crustal deformation showed that the Iznik-Mekece fault segment moves westward at about 22 ± 1 mm/yr with respect to the Eurasia fixed reference frame. The GPS observations show that there is no strain accumulation in the area.     

Scattering coefficients in the mantle revealed from the seismogram envelope analysis based on the multiple isotropic scattering model

At longer periods, scattered ScS waves sometimes dominate over coda waves at large lapse times. Examining recordings of seismic envelopes at 9 IRIS seismic stations of regional earthquakes with focal depths deeper than 150 km in periods from 1 to 20 s for a wide lapse time range up to 2000 s, we found significant frequency dependence. The coda decay gradient at short periods is steeper than that at longer periods; however, the change of coda gradient associated with the ScS arrival becomes distinct as the period becomes longer. In particular, a clear offset of coda amplitude appears in central Asia for 10 and 15 s period bands. The multiple isotropic scattering process of S-waves in the heterogeneous mantle can be simply simulated by using the Monte Carlo simulation method based on the radiative transfer theory in scattering media. Assuming a two-plane-layer attenuation structure and smoothed velocity model of the PREM, we estimated the average total scattering coefficients of S-waves such as 7.52 × 10^− 4∼1.32 × 10^− 3 km^− 1 and 2.08 × 10^− 4∼6.23 × 10^− 4 km^− 1 at 4 s, and 4.51 × 10^− 4∼7.37 × 10^− 4 km^− 1 and 2.80 × 10^− 5∼2.71 × 10^− 4 km^− 1 at 10 s, for the lithosphere and the upper mantle and for the lower mantle, respectively. Our results indicate that scattering occurs mostly in the lithosphere and the upper mantle and support that medium heterogeneity spreads over the whole mantle though its scattering power is small. Strong scattering occurs beneath central Asia and Papua New Guinea, whereas the scattering beneath Italy and regions of east Russia is much weaker. The numerical calculation enables us to confirm that much stronger scattering than intrinsic attenuation causes the offset behavior with coda decay gradient change after the ScS arrival for 4 and 10 s period bands in some regions.     

Processing and interpretation of vintage 2D marine seismic data from the outer Hanö Bay area,Baltic Sea

A grid of previously unpublished, vintage 2D marine seismic lines has been processed and interpreted to the east of Hanö Bay, SW Baltic Sea. The 3200 km² study area lies on the transition between the Hanö Bay Basin to the West and Baltic Synelcise to the East, NE of the Tornquist intra shield tectonic zone.Data from the NA79, NA80 and RW84 surveys were selected for this study from the extensive Oljeprospektering AB (OPAB) Baltic Sea dataset. New processing workflows have been developed for the data which focus on suppressing two significant forms of noise, namely multiple and side scattered noise. Deconvolution in the tau-p domain, parabolic radon demultiple and post stack deconvolution are shown to be effective at attenuating multiple noise, while FK filtering in shot and receiver gathers is effective at removing side scattered noise.The newly processed data were interpreted and a series of maps detailing the structure of the basement, Cambrian and Silurian/Paleozoic horizons were constructed. These maps differ significantly to previously published interpretations of the area. Within the study area, a region of significant Late Carboniferous/Early Permian transtensional faulting and Late Cretaceous inversion is mapped in detail. This structure would have exhibited normal offsets of up to 600 m before inversion with later inverted displacements of up to approximately 200 m in places. This feature appears to extend some 20 km to the SW of the study area to the major fault bounding the Christiansø High. Based on the seismic interpretation, the area appears to have had a similar overall geological history as the adjacent Tornquist Zone to the SW.     

Bayesian analysis on earthquake magnitude related to an active fault in Taiwan

It is understood that sample size could be an issue in earthquake statistical studies, causing the best estimate being too deterministic or less representative derived from limited statistics from observation. Like many Bayesian analyses and estimates, this study shows another novel application of the Bayesian approach to earthquake engineering, using prior data to help compensate the limited observation for the target problem to estimate the magnitude of the recurring Meishan earthquake in central Taiwan. With the Bayesian algorithms developed, the Bayesian analysis suggests that the next major event induced by the Meishan fault in central Taiwan should be in M_w 6.44±0.33, based on one magnitude observation of M_w 6.4 from the last event, along with the prior data including fault length of 14 km, rupture width of 15 km, rupture area of 216 km², average displacement of 0.7 m, slip rate of 6 mm/yr, and five earthquake empirical models.     

Sea level rise in the north-western part of the Arabian Gulf

Relative sea level variations in the north-western part of the Arabian Gulf have been estimated in the past using no more than 10 to 15 years of observations. In this study, we have almost doubled the period to 28.7 years by examining all available tide gauge data in the area and constructing a mean gauge time-series from seven coastal tide gauges. We found for the period 1979–2007 a relative sea level rise of 2.2 ± 0.5 mm/year. Using the subsidence observed at 6 GPS stations within a radius of 100 km of the tide gauges as an indication of the vertical land motion, the corresponding absolute sea level rise is 1.5 ± 0.8 mm/year that is in agreement with the global estimate of 1.9 ± 0.1 mm/year (Church and White, 2011) for the same studied period. By taking into account the temporal correlations we conclude that previous published results underestimate the true sea level rate uncertainty in this area by a factor of 5–10.     

GPS constraints on the deformation of Azerbaijan and surrounding regions

In this study, we present new GPS observations in Azerbaijan to provide an improved basis for determining the distribution of crustal deformation throughout the country and surrounding areas. The deformation field in the region has been analyzed with a dense GPS network configuration and a reliable quantification of the ongoing deformation was achieved. Results show that while contraction is dominant over the whole region, it is mostly concentrated on the middle and eastern parts of Caucasus Thrust Fault reaching up to 6.4 ± 0.2 mm/yr and Lesser Caucasus Fault does no accommodate more than 1–2 mm/yr of contraction. New network also clearly substantiates that the West Caspian Fault, which is a continuation of Caucasus Thrust Fault in the south, accommodates right-lateral slip rates of 7.1 ± 0.3 mm/yr in addition to 5.5 ± 0.3 mm/yr contraction rates.     

The Masaya Triple Layer: A 2100 year old basaltic multi-episodic Plinian eruption from the Masaya Caldera Complex (Nicaragua)

The Masaya Caldera Complex has been the site of three highly explosive basaltic eruptions within the last six thousand years. A Plinian eruption ca. 2 ka ago formed the widespread deposits of the Masaya Triple Layer. We distinguish two facies within the Masaya Triple Layer from each other: La Concepción facies to the south and Managua facies to the northwest. These two facies were previously treated as two separated deposits (La Concepción Tephra and the Masaya Triple Layer of Pérez and Freundt, 2006) because of their distinct regional distribution and internal architectures. However, chemical compositions of bulk rock, matrix and inclusion glasses and mineral phases demonstrate that they are the product of a single basaltic magma batch. Additionally, a marker bed containing fluidal-shaped vesicular lapilli allowed us to make a plausible correlation between the two facies, also supported by consistent lateral changes in lithologic structure and composition, thickness and grain size.We distinguish 10 main subunits of the Masaya Triple Layer (I to X), with bulk volumes ranging between 0.02 and 0.22 km³, adding up to 0.86 km³ (0.4 km³ DRE) for the entire deposit. Distal deposits identified in two cores drilled offshore Nicaragua, at a distance of ～ 170 km from the Masaya Caldera Complex, increase the total tephra volume to 3.4 km³ or ～ 1.8 km³ DRE of erupted basaltic magma.Isopleth data of five major fallout subunits indicate mass discharges of 10⁶ to 10⁸ kg/s and eruption columns of 21 to 32 km height, affected by wind speeds of < 2 m/s to ～ 20 m/s which increased during the course of the multi-episodic eruption. Magmatic Plinian events alternated with phreatoplinian eruptions and phreatomagmatic explosions generating surges that typically preceded breaks in activity. While single eruptive episodes lasted for few hours, the entire eruption probable lasted weeks to months. This is indicated by changes in atmospheric conditions and ash-layer surfaces that had become modified during the breaks in activity. The Masaya Triple Layer has allowed to reconstruct in detail how a basaltic Plinian eruption develops in terms of duration, episodicity, and variable access of external water to the conduit, with implications for volcanic hazard assessment.     

Two extraterrestrial dust horizons found in the Dome Fuji ice core,East Antarctica

Two silicate-rich dust layers were found in the Dome Fuji ice core in East Antarctica, at Marine Isotope Stages 12 and 13. Morphologies, textures, and chemical compositions of constituent particles reveal that they are high-temperature melting products and are of extraterrestrial origin. Because similar layers were found ～ 2000 km east of Dome Fuji, at EPICA (European Project for Ice Coring in Antarctica)-Dome C, particles must have rained down over a wide area 434 and 481 ka. The strewn fields occurred over an area of at least 3 × 10⁶ km². Chemical compositions of constituent phases and oxygen isotopic composition of olivines suggest that the upper dust layer was produced by a high-temperature interaction between silicate-rich melt and water vapor due to an impact explosion or an aerial burst of a chondritic meteoroid on the inland East Antarctic ice sheet. An estimated total mass of the impactor, on the basis of particle flux and distribution area, is at least 3 × 10⁹ kg. A possible parent material of the lower dust layer is a fragment of friable primitive asteroid or comet. A hypervelocity impact of asteroidal/cometary material on the upper atmosphere and an explosion might have produced aggregates of sub-μm to μm-sized spherules. Total mass of the parent material of the lower layer must exceed 1 × 10⁹ kg. The two extraterrestrial horizons, each a few millimeters in thickness, represent regional or global meteoritic events not identified previously in the Southern Hemisphere.     

Systematic tapping of independent magma chambers during the 1 Ma Kidnappers supereruption

The 1.0 Ma Kidnappers supereruption (~ 1200 km³ DRE) from Mangakino volcanic centre, Taupo Volcanic Zone, New Zealand, produced a large phreatomagmatic fall deposit followed by an exceptionally widespread ignimbrite. Detailed sampling and analysis of glass shards and mineral phases have been undertaken through a proximal 4.0 m section of the fall deposit, representing the first two-thirds of erupted extra-caldera material. Major and trace element chemistries of glass shards define three distinct populations (types A, B and C), which systematically change in proportion through the fall deposit and are inferred to represent three magma types. Type B glass and biotite first appear at the same level (~ 0.95 m above base) in the fall deposit suggesting later tapping of a biotite-bearing magma. Plagioclase and Fe–Ti oxide compositions show bimodal distributions, which are linked to types A and B glass compositions. Temperature and pressure (T–P) estimates from hornblende and Fe–Ti oxide equilibria from each magma type are similar and therefore the three magma bodies were adjacent, not vertically stacked, in the crust. Most hornblende model T–P estimates range from 770 to 840 °C and 90 to 170 MPa corresponding to storage depths of ~ 4.0–6.5 km. Hornblende model T–P estimates coupled with in situ trace element fingerprinting imply that the magma bodies were individually well mixed, and not stratified. Compositional gaps between the three glass compositional types imply that no mixing between these magmas occurred. We interpret these data, coupled with the systematic changes in shard compositional proportions through the fall deposit, to reflect that three independent melt-dominant bodies of magma contributed large (A, ~ 270 km³), medium (B, ~ 90 km³) and small (C, ~ 40 km³) volumes (as reflected in the fall deposits) and were systematically tapped during the eruption. We propose that the systematic evacuation of the three independent magma bodies implies that there was tectonic triggering and linkage of eruptions. Our results show that supereruptions can be generated by near simultaneous multiple eruptions from independent magma chambers rather than the evacuation of a large single unitary magma chamber.     

Zircon U–Pb strain chronometry reveals deep impact-triggered flow

Large (> 100 km) meteorite impact cratering events play important roles in surface and biosphere evolution, however, their potential for widespread ductile modification of the lithosphere has been difficult to assess, due partly to our inability to isotopically age-correlate deep mineral fabrics with surface records. We have integrated benchmark U–Pb zircon dating methods (ID-TIMS, SHRIMP) with new microstructural techniques (EBSD, µXRD) to demonstrate that crystal–plastic deformation can cause rapid out-diffusion of radiogenic Pb and accompanying trace element alteration in crystalline zircon. We have used this phenomenon to directly date fabric in Archean zircons and xenoliths of the lower crust of South Africa at 2023 ± 15 million years, coeval with the 2020 ± 3 million year old Vredefort cratering event at surface, with extent ≥ 20,000 km². Our findings indicate that regional exogenic fabrics, similar to high-temperature tectonic fabrics, exist in ancient crust. Moreover, our results establish that crystal-plastic deformation in the lithosphere can now be directly dated and linked to planetary evolution by zircon U–Pb strain chronometry.     

Factors controlling sediment yield in a major South American drainage basin: the Magdalena River,Colombia

The Magdalena River, a major fluvial system draining most of the Colombian Andes, has the highest sediment yield of any medium-sized or large river in South America. We examined sediment yield and its response to control variables in the Magdalena drainage basin based on a multi-year dataset of sediment loads from 32 tributary catchments. Various morphometric, hydrologic, and climatic variables were estimated in order to understand and predict the variation in sediment yield. Sediment yield varies from 128 to 2200 t km⁻² yr⁻¹ for catchments ranging from 320 to 59,600 km². The mean sediment yield for 32 sub-basins within the Magdalena basin is ∼690 t km⁻² yr⁻¹. Mean annual runoff is the dominant control and explains 51% of the observed variance in sediment yield. A multiple regression model, including two control variables, runoff and maximum water discharge, explains 58% of the variance. This model is efficient (ME=0.89) and is a valuable tool for predicting total sediment yield from tributary catchments in the Magdalena basin. Multiple correlations for those basins corresponding to the upper Magdalena, middle basin, Eastern Cordillera, and catchment areas greater than 2000 km², explain 75, 77, 89, and 78% of the variance in sediment yield, respectively. Although more variance is explained when dataset are grouped into categories, the models are less efficient (ME<0.72). Within the spatially distributed models, six catchment variables predict sediment yield, including runoff, precipitation, precipitation peakedness, mean elevation, mean water discharge, and relief. These estimators are related to the relative importance of climate and weathering, hillslope erosion, and fluvial transport processes. Time series analysis indicates that significant increases in sediment load have occurred over 68% of the catchment area, while 31% have experienced a decreasing trend in sediment load and thus yield. Land use analysis and increasing sediment load trends indicate that erosion within the catchment has increased over the last 10–20 years.     

New insights in the geodynamics of the Lipari–Vulcano area (Aeolian Archipelago,southern Italy) from geological,geodetic and seismological data

Geological, geodetic and seismological data have been analyzed in order to frame the Lipari–Vulcano complex (Aeolian archipelago, southern Italy) into the geodynamic context of the southeastern Tyrrhenian Sea. It is located at the northern end of a major NNW–SSE trending right-lateral strike-slip fault system named “Aeolian–Tindari–Letojanni” which has been interpreted as a lithospheric discontinuity extending from the Aeolian Islands to the Ionian coast of Sicily and separating two different tectonic domains: a contractional one to the west and an extensional one to the north-east. Structural field data consist of structural measurements performed on well-exposed fault planes and fractures. The mesostructures are mostly represented by NW–SE striking normal faults with a dextral-oblique component of motion. Minor structures are represented by N–S oriented joints and tension gashes widespread over the whole analyzed area and particularly along fumarolized sectors. The analyzed seismological dataset (from 1994 to 2013) is based on earthquakes with magnitude ranging between 1.0 and 4.8. The hypocenter distribution depicts two major alignments corresponding to the NNW–SSE trending Aeolian–Tindari–Letojanni fault system and to the WNW–ESE oriented Sisifo–Alicudi fault system. GPS data analysis displays ∼3.0 mm/yr of active shortening between the two islands, with a maximum shortening rate of about 1.0 × 10⁻¹³ s⁻¹, between La Fossa Caldera and south of Vulcanello. This region is bounded to the north by an area where the maximum values of shear strain rates, of about 0.7 × 10⁻¹³ s⁻¹ are observed. This major change occurs in the area south of Vulcanello that is also characterized by a transition in the way of the vertical axis rotation. Moreover, both the islands show a clear subsidence process, as suggested by negative vertical velocities of all GPS stations which exhibit a decrease from about −15 to −7 mm/yr from north to south. New data suggest that the current kinematics of the Lipari–Vulcano complex can be framed in the tectonic context of the eastward migrating Sisifo–Alicudi fault system. This is dominated by transpressive tectonics in which contractional and minor extensional structures can coexist with strike-slip motion.     

Inferred fault geometry and slip distribution of the 2010 Jiashian,Taiwan, earthquake is consistent with a thick-skinned deformation model

We invert measurements of coseismic displacements from 139 continuously recorded GPS sites from the 2010, Jiashian, Taiwan earthquake to solve for fault geometry and slip distribution using an elastic uniform stress drop inversion. The earthquake occurred at a depth of ~ 23 km in an area between the Western Foothills fold-and-thrust belt and the crystalline high mountains of the Central Range, providing an opportunity to examine the deep fault structure under Taiwan. The inferred rupture plane is oblique to the prominent orientation of thrust faults and parallel to several previously recognized NW-striking transfer zones that appear to connect stepping thrusts. We find that a fault striking 318°–344° with dip of 26°–41° fits the observations well with oblique reverse-sinistral slip under a low stress drop of about 0.5 MPa. The derived geodetic moment of 2.92 × 10¹⁸ N-m is equivalent to a M_w = 6.24 earthquake. Coseismic slip is largely concentrated within a circular patch with a 10-km radius at the depth between 10 and 24 km and maximum slip of 190 mm. We suggest this earthquake ruptured the NW-striking Chishan transfer fault zone, which we interpret as a listric NE-dipping lateral ramp with oblique slip connecting stepping thrust faults (ramps). The inferred slip on the lateral ramp is considerably deeper than the 7–15 km deep detachment identified in previous studies of western Taiwan. We infer an active basal detachment under western Taiwan at a depth of at least ~ 20–23 km based on these inversion results. The earthquake may have nucleated at the base of the lateral ramp near the intersection with the basal detachment. Coulomb stress change calculations suggest that this earthquake moved several NE-striking active thrust faults in western Taiwan nearer to failure.     

Distributions,possible sources and biological risk of DDTs,HCHs and chlordanes in sediments of Beibu Gulf and its tributary rivers,China

Thirty-five surface sediment samples collected from Beibu Gulf and its tributary rivers, China were analyzed for DDTs, HCHs and chlordanes. Total concentrations of DDTs, HCHs and chlordanes in sediments ranged from 0.59 to 126 ng g⁻¹, ND to 2.65 ng g⁻¹ and 0.27 to 3.41 ng g⁻¹ based on dry weight (dw), respectively. Concentrations of DDTs were higher than those reported in the sediments from other regions of the world, while concentrations of HCHs and chlordanes were relatively low. High concentrations of DDTs were observed in the harbor region and aquaculture bases and high concentrations of HCHs were found in the Qin River Estuary. The ratios of (DDE + DDD)/DDTs reflected a mixed input of weathered and fresh DDTs. The predominant β-HCH indicated that HCHs in the study area mainly originated from the historical usage of technical HCH. The residues of DDTs would pose adverse biological effects on the study area.