Active segment of the 12 November 2003 Mw 5.6 earthquake at Salsipuedes oceanic basin,Gulf of California. Mexico

We analyzed records of eight seismic stations of the autonomous broadband seismograph network of a joint project between Utrecht University (the Netherlands), California Institute of Technology, and Centro de Investigación Científica y de Estudios Superiores de Ensenada (CICESE). These stations recorded the Mw 5.6 earthquake that occurred on 12 November 2003 at Salsipuedes basin in the middle of the Gulf of California 2 km west of the island Angel de la Guarda. This event was located at 29.16º N and 113.37º W, 30 km northeast of Bahia de los Angeles. A foreshock and hundreds of aftershocks were recorded in the 48 hours after its origin time. With the location of 29 earthquakes we identified the active segment, perpendicular to the main transform fault NW–SE of Canal de Ballenas, representing the transtensional boundary between the Pacific and North American plates. The direction of the active fault described is consistent with the normal fault mechanism reported by the National Earthquake Information Center (strike=39º, dip=34º, slip=–44º).From the duration magnitude of 456 aftershocks, we calculated a b-value of 1.14±0.28; furthermore, we calculated a seismic moment of (3.5 ±3.3) X10¹⁷Nm, a source radius of 3.7 ± 2.63 km, and a static stress drop of 3.94 ± 1.15 MPa (39.4 ± 11.5 bar.).     

The equivalent dose of different grain size quartz fractions from lakeshore sediments in the arid region of north China

Equivalent dose (D_e) values were measured by using medium aliquots of different grain size quartz fractions of five lakeshore sediments from the arid region of north China. There are two different relationships between D_e values and grain sizes of these five samples. The first relationship is that the D_e values obtained from various grain sizes are in agreement within 1 delta errors. The second relationship is that D_e values are similar to each other for fractions between 125 and 300 μm, while the D_e value of the 63–90 μm fraction is 40～55% smaller than others. For example, the D_e values obtained for sample #3 are 20.15 ± 1.19 Gy, 19.80 ± 0.83 Gy and 20.93 ± 1.06 Gy for fractions of 90–125, 125–150 and 250–300 μm respectively, but are 10.79 ± 0.84 Gy for the 63–90 μm fraction. The second relationship can't be interpreted by previous studies of both dosimetry and heterogeneous bleaching. It is deduced for sample #2, #3 and #6 that fine particles (<90 μm) intruded after the dominant sedimentation. Comparison of OSL ages from different grain size fractions of sample #2 with a radiocarbon age from the same lithologic layer supports that fractions coarser than 125 μm yield more reliable burial ages, while the fraction finer than 90 μm yields underestimated ages for some lakeshore sediments from this arid region.     

Copper toxicity in the marine copepod Tigropus japonicus: Low variability and high reproducibility of repeated acute and life-cycle tests

The intertidal copeopod Tigriopus japonicus, which is abundant and widely distributed along the coasts of Western Pacific, has been suggested to be a good marine ecotoxicity testing organism. In this study, a series of experiments were conducted to investigate the reproducibility and variability of copper (Cu) sensitivity of T. japonicus so as to evaluate its potential to serve as an appropriate test species. To understand the seasonal variation of Cu sensitivity, individuals of T. japonicus were collected from the field in summer and winter, and subjected to standard 96 h acute (static renewal) toxicity tests. 96 h-LC50 values of T. japonicus collected from the two seasons were marginally different (p = 0.05), with an overall coefficient of variation (CV) of 33%. Most importantly, our results indicated that chronic Cu sensitivity of T. japonicus was highly reproducible. The CVs of intrinsic rates of increase in the population of the control and Cu treatment (10 μg Cu l⁻¹) groups were only 10–11% between 10 runs of a standardised complete life-cycle test. Moreover, different Cu(II) salts generally resulted in a similar 96 h-LC50 value while Cu(I) chloride was consistently slightly less toxic than Cu(II) salts. Given such a high reproducibility of toxic responses, it is advocated to use T. japonicus as a routine testing organism.     

Artificial earthquake test of gas supply networks

In this paper, seismic behavior of gas supply networks is investigated by constructing a 24 m×24 m buried network and conducting an artificial earthquake test by detonating TNT explosives. The pipe network consists of typical welded steel pipes used in gas supply networks. Ground motion is produced by detonating 30 kg of TNT explosives buried 5 m below ground surface and 15 m away from the network. The test preparations are presented, including site selection, network layout, ground motion generation, and arrangements of different sensors. The measured ground acceleration, strain, and acceleration of welded steel pipes, and pipe–soil relative slippage are discussed. The deformation patterns of welded steel pipes are also analyzed and explained, including axial and bending deformations, systematic network characteristics, deformation relationship between ground and pipes, and dynamic response of buried pipes.     

Precursory signatures in the visibility graph analysis of seismicity: An application to the Kachchh (Western India) seismicity

The Visibility Graph (VG) method maps time series into networks or graphs, converting dynamical properties of time series in topological properties of networks. The VG method was applied to the aftershock depleted catalogue of the Kachchh Gujarat (Western India) seismicity from 2003 to 2012, in order to identify possible precursory signatures in the pattern of the VG parameters. The k–M slope (the slope of the line fitting the relationship between the magnitude of the events and their connectivity degrees) seems to sharply increase significantly before the occurrence of the largest shocks (M ⩾ 4.5) of the sequence.     

Liquefaction assessment of cohesionless soils in the vicinity of large embankments

In a typical seismic dam safety evaluation, standard penetration, cone penetration, Becker penetration, or shear wave velocity (V_s) tests are often first conducted near the toe of an earth dam to infer if any liquefiable soil exists in the foundation of the dam footprint. In current practice, a level-ground condition is commonly assumed when normalizing penetration resistance and V_s, and may be assumed (particularly in preliminary assessments) in applying the cyclic stress method (with or without the K_α correction) to evaluate liquefaction. However, the presence of an earth dam, or any other large embankment or structure, significantly alters the normal and shear stresses in the foundation. This paper identifies and quantifies potential errors in ignoring altered stresses near heavy structures, and presents a methodology to incorporate these effects within the framework of the simplified procedure. Specifically, the effects of these altered stresses (in comparison to the level-ground assumption with and without K_α correction) on the: (1) normalization of field measurements such as penetration resistance and V_s; (2) cyclic stress ratio (CSR); (3) cyclic resistance ratio (CRR); and (4) factor of safety against liquefaction triggering (FS_liq), are evaluated by considering static and dynamic analyses of a generic earthen embankment (60 m high) resting on a saturated, cohesionless foundation (30 m deep). Our analyses indicated that ignoring the presence of induced static shear stresses can result in potentially unconservative errors in overburden correction factors of 30% to 60% at shallow depth (although this error is greatly muted at depths exceeding about 15 m), while errors in CSR potentially can range from about 20% too conservative to 40% unconservative. Potential errors in CRR can approach 50% unconservative at shallow depths, but again, this error is muted at depths exceeding about 15 m. Combining these factors, potentially unconservative errors in computing FS_liq could exceed 100% at shallow depths (less than 15 m to 20 m) while at greater depth (exceeding 20 m) errors approach 20% on the conservative side.     

Reflection seismic imaging of the end-glacial Pärvie Fault system,northern Sweden

Reflection seismic data were acquired along a c. 23 km long profile over the Pärvie Fault system with a nominal receiver and source spacing of 20 m. An hydraulic breaking hammer was used as a source, generating signals with a penetration depth of about 5–6 km. Steeply dipping reflections from the end-glacial faults are observed, as well as sub-horizontal reflections. The location and orientation of the reflections from the faults agree well with surface geological observations of fault geometries. Reflections from a potential fourth end-glacial fault is observed further to the east along the profile. The more sub-horizontal reflections may originate from gabbroic bodies within the granitic basement or from deeper lying greenstones. Our results indicate that the end-glacial faults dip at moderate to steep dips down to at least 2–3 km depth, and possibly continue at this dip to depths of 6 km. This result has significant implications for determining the state of stress required to activate the faults in the past and in the future.     

Low-degree melting of a metasomatized lithospheric mantle for the origin of Cenozoic Yulong monzogranite-porphyry,east Tibet: Geochemical and Sr–Nd–Pb–Hf isotopic constraints

SHRIMP zircon U–Pb dating, mineral chemical, element geochemical and Sr–Nd–Pb–Hf isotopic data have been determined for the Yulong monzogranite-porphyry in the eastern Tibet, China. The Yulong porphyry was emplaced into Triassic strata at about 39 Ma. The rocks are weakly peraluminous and show shoshonitic affinity, i.e., alkalis-rich, high K₂O contents with high K₂O / Na₂O ratios, enrichment in LREE and LILE. They also show some affinities with the adakite, e.g., high SiO₂ and Al₂O₃, and low MgO contents, depleted in Y and Yb, and enrichment in Sr with high Sr / Y and La / Yb ratios, and no Eu anomalies. The Yulong porphyry has radiogenic ⁸⁷Sr / ⁸⁶Sr (0.7063–0.7070) and unradiogenic ¹⁴³Nd / ¹⁴⁴Nd (ε_Nd = − 2.0 to − 3.0) ratios. The Pb isotopic compositions of feldspar phenocrysts separated from the Yulong porphyry show a narrow range of ²⁰⁶Pb / ²⁰⁴Pb ratios (18.71–18.82) and unusually radiogenic ²⁰⁷Pb / ²⁰⁴Pb (15.65–15.67) and ²⁰⁸Pb / ²⁰⁴Pb (38.87–39.00) ratios. In situ Hf isotopic composition of zircons that have been SHRIMP U–Pb dated is characterized by clearly positive initial ε_Hf values, ranging from + 3.1 to + 5.9, most between + 4 and + 5. Phenocryst clinopyroxene geothermometry of the Yulong porphyry indicates that the primary magmas had anomalously high temperature (> 1200 °C). The source depth for the Yulong porphyry is at least 100 km inferred by the metasomatic volatile phase (phlogopite–carbonate) relations. Detailed geochemical and Sr–Nd–Pb–Hf isotopic compositions not only rule out fractional crystallization or assimilation-fractional crystallization processes, but also deny the possibility of partial melting of subducted oceanic crust or basaltic lower crust. Instead, low degree (1–5%) partial melting of a metasomatized lithosphere (phlogopite–garnet clinopyroxenite) is compatible with the data. This example gives a case study that granite can be derived directly by partial melting of an enriched lithospheric mantle, which is important to understand the source and origin of diverse granites.     

Formation of elongated granite–migmatite domes as isostatic accommodation structures in collisional orogens

The mid-Carboniferous Pelhřimov core complex, Bohemian Massif, is a crustal-scale elongated granite–migmatite dome interpreted to have formed by gravity-driven diapiric upwelling of the metapelitic middle crust. The vertical diapiric flow is evidenced by outward-dipping foliation and lineation patterns, deformation coeval with the widespread presence of melt, rapid exhumation of the dome center from depths corresponding to pressure of about 0.6 GPa to shallow levels (pressure less than 0.2 GPa) within 2 M.y., and kinematic indicators of downward return flow of the mantling rocks. As compared to common diapirs, however, the Pelhřimov complex exhibits a more complicated inferred strain pattern with two perpendicular, irregularly alternating directions of horizontal extension in what is interpreted as the diapir head. Comparison of structural data from migmatites with anisotropy of magnetic susceptibility (AMS) data in granites also reveals that only final increments of strain are recorded in the granites. The map dimensions and gravity image of the complex suggest that the diapiric upwelling affected a large portion of the orogen's interior between two microplates brought together during continental collision. The northwesterly microplate (the upper-crustal Teplá–Barrandian unit) collapsed vertically as an ‘elevator’ at around 346–337 Ma whereas the easterly microplate (Brunia) was underthrust beneath the Moldanubian rocks during ∼346–330 Ma (the indentor). It is suggested that these microplates then acted as cold and rigid margins localizing mid-crustal diapirism and associated voluminous S-type granite plutons inbetween, parallel to the edge of the Brunia indentor.We conclude that bringing together soft metapelitic middle crust with two rigid lithospheric blocks during collision resulted in significant lateral temperature and strength variations across the orogen's interior. A general conclusion from these inferences is that granite–migmatite domes delineating margins of collided microplates may form as crustal-scale structures accommodating late-orogenic isostatic reequilibration.     

Spectral attenuation of solar radiation in Patagonian fjord and coastal waters and implications for algal photobiology

The spectral attenuation of solar irradiation was measured during summer in two types of coastal waters in southern Chile, a north Patagonian fjord (Seno Reloncaví) and open coast (Valdivia). In order to relate the light availability with the light requirements of upper subtidal seaweeds, the saturating irradiance for photosynthesis (E_k) from P–I curves was measured. In addition the UV risk was assessed. Based on the z_1% of PAR, the lower limit of the euphotic zone in the studied systems averaged 21 m (K_d 0.24 m^?1) in Seno Reloncaví and 18 m (K_d 0.27 m^?1) in the coast of Valdivia. Photosynthesis of the studied seaweeds was saturated at markedly lower irradiances than found in their natural depths at the time of the study. Solar radiation penetrating into these depths at both locations largely supports the light requirements for the photosynthesis of subtidal species: 50–160 μmol m^?2 s^?1 for seaweeds from Seno Reloncaví (7 m tidal range) and 20–115 μmol m^?2 s^?1 for Valdivia assemblages (2 m tidal range). Optimal light conditions to saturate photosynthesis (E_k) were present at 10–16 m water depth. The attenuation of solar irradiation did not vary significantly between the fjord and coastal sites of this study. However, the underwater light climates to which seaweeds are exposed in these sites vary significantly because of the stronger influence of tidal range affecting the fjord system as compared with the open coastal site. The patterns of UV-B penetration in these water bodies suggest that seaweeds living in upper littoral zones such as the intertidal and shallow subtidal (<3 m) may be at risk.     

Characteristics and role of groundwater dissolved organic matter on arsenic mobilization and poisoning in Bangladesh

The fluorescence and molecular weight characteristics of dissolved organic matter (DOM) in groundwater of Bangladesh were investigated to evaluate its multiple roles on arsenic (As) mobilization and poisoning. Fluorescence properties of DOM were measured in groundwater samples collected from two As contaminated areas of Bangladesh (Faridpur at the Ganges floodplain and Sonargaon at the Meghna floodplain) from different locations and depths. The three dimensional excitation–emission matrix (3DEEM) fluorescence spectra of groundwater samples showed two characteristic peaks around Ex/Em = 335–365 nm/435–480 nm for fulvic-like peaks and peak at around Ex/Em = 275–290 nm/310–335 nm for the protein-like materials. The similarity of fluorescence spectra of groundwater and surface water of both the study areas with high intensity of fluorescence and its strong correlation with DOC reflect the in situ generation of fluorescent DOM from sedimentary organic matter (SOM) and recent recharge of terrestrial labile organic carbon into shallow aquifer. High performance size-exclusion chromatography (HPSEC) analysis of DOM shows positive correlations between fluorescence intensities (FI) of small molecular fractions (0.65 kDa) and As concentrations, with the signatures of protein-like peaks of DOM in groundwater. This result provides new evidence that small molecular weight fraction of DOM in groundwater of Bangladesh can play an important role on As mobilization and toxicity. In addition, high concentration of fluorescence materials in DOM of As contaminated groundwater of Bangladesh may pose a threat to public health.     

A new electrical and mechanically detonatable shear wave source for near surface (0–30 m) seismic acquisition

We present a new, impulsive, horizontal shear source capable of performing long shot profiles in a time-efficient and repeatable manner. The new shear source is ground-coupled by eight 1/2″ (1.27 cm) × 2″ (5.08 cm) steel spikes. Blank shotshells (12-gauge) used as energy sources can be either mechanically or electrically detonated. Electrical fuses have a start time repeatability of < 50 μs. This source can be operated by a single individual, and takes only ~ 10 s between shots as opposed to ~ 30 s for six stacked hammer blows. To ensure complete safety, the shotshell holder is surrounded by a protective 6″ (15.24 cm)-thick barrel, a push-and-twist-locked breach, and a safety pin.We conducted field tests at the 17th Street Canal levee breach site in New Orleans, Louisiana (30.017° N 90.121° W) and at an instrumented test borehole at Millsaps College in Jackson, Mississippi (32.325° N 93.182° W) to compare our new source and a traditional hammer impact source. The new shear source produces a broader-band of frequencies (30–100 Hz cf. 30–60 Hz). Signal generated by the new shear source has signal-to-noise ratios equivalent to ~ 3 stacked hammer blows to the hammer impact source. Ideal source signals must be broadband in frequency, have a high SNR, be consistent, and have precise start times; all traits of the new shear source.     

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.     

Crustal seismic structure and depth distribution of earthquakes in the Archean Kuusamo region,Fennoscandian Shield

Two-dimensional crustal velocity models are derived from passive seismic observations for the Archean Karelian bedrock of north-eastern Finland. In addition, an updated Moho depth map is constructed by integrating the results of this study with previous data sets. The structural models image a typical three-layer Archean crust, with thickness varying between 40 and 52 km. P wave velocities within the 12–20 km thick upper crust range from 6.1 to 6.4 km/s. The relatively high velocities are related to layered mafic intrusive and volcanic rocks. The middle crust is a fairly homogeneous layer associated with velocities of 6.5–6.8 km/s. The boundary between middle and lower crust is located at depths between 28 and 38 km. The thickness of the lower crust increases from 5–15 km in the Archean part to 15–22 km in the Archean–Proterozoic transition zone. In the lower crust and uppermost mantle, P wave velocities vary between 6.9–7.3 km/s and 7.9–8.2 km/s. The average V_p/V_s ratio increases from 1.71 in the upper crust to 1.76 in the lower crust.The crust attains its maximum thickness in the south-east, where the Archean crust is both over- and underthrust by the Proterozoic crust. A crustal depression bulging out from that zone to the N–NE towards Kuusamo is linked to a collision between major Archean blocks. Further north, crustal thickening under the Salla and Kittilä greenstone belts is tentatively associated with a NW–SE-oriented collision zone or major shear zone. Elevated Moho beneath the Pudasjärvi block is primarily explained with rift-related extension and crustal thinning at ∼2.4–2.1 Ga.The new crustal velocity models and synthetic waveform modelling are used to outline the thickness of the seismogenic layer beneath the temporary Kuusamo seismic network. Lack of seismic activity within the mafic high-velocity body in the uppermost 8 km of crust and relative abundance of mid-crustal, i.e., 14–30 km deep earthquakes are characteristic features of the Kuusamo seismicity. The upper limit of seismicity is attributed to the excess of strong mafic material in the uppermost crust. Comparison with the rheological profiles of the lithosphere, calculated at nearby locations, indicates that the base of the seismogenic layer correlates best with the onset of brittle to ductile transition at about 30 km depth.We found no evidence on microearthquake activity in the lower crust beneath the Archean Karelian craton. However, a data set of relatively well-constrained events extracted from the regional earthquake catalogue implies a deeper cut-off depth for earthquakes in the Norrbotten tectonic province of northern Sweden.     

Systematic deflection and offset of the Yangtze River drainage system along the strike-slip Ganzi-Yushu-Xianshuihe Fault Zone,Tibetan Plateau

The Ganzi-Yushu-Xianshuihe Fault Zone (GYXFZ) is a typical active strike-slip fault that has triggered many large historic earthquakes, including the 2010 M_w 6.9 Yushu earthquake in the central Tibetan Plateau. This fault zone extends for ca. 800 km from the central Tibetan Plateau to its southeastern margin and varies in trend from WNW-ESE in the northwestern segment of the fault zone to NNW-SSE in the southeastern segment, having the geometry of an arc projecting northeastwards. In this study, we present evidence for the systematical sinistral deflection and/or offset of the Yangtze River and its branch stream channels and valleys along the GYXFZ. Topographic analysis of three-dimensional (3D) perspective images constructed using digital elevation model (DEM) data, 0.5 m-resolution WorldView and GeoEye images, and 15 m-resolution Landsat-Enhanced Thematic Mapper (ETM+) images, together with analysis of geological structures, reveals the following: (i) the main river channels and valleys of the Yangtze River drainage system show systematic sinistral deflections and/or offsets along the GYXFZ; (ii) various amounts of sinistral offset have accumulated on the tributary stream channels, valleys, and gullies of the Yangtze River along the fault, with a linear relation, D = aL, between the upstream length L from the deflected point and the offset amount D with a certain coefficient a; (iii) the maximum amount of sinistral offset is up to ca. 60 km, which was accumulated in the past 13–5 Ma; and (iv) the long-term average strike-slip rate is ca. 4.6–12 mm/year. Geological and geomorphic evidence, combined with geophysical data, demonstrates that the GYXFZ is currently active as one of the major seismogenic faults in the Tibetan Plateau, dominated by left-lateral strike-slip motion. Our findings supply important evidence for the tectonic evolution of strike-slip faults in the Tibetan Plateau since the Eurasia-India continental collision.     

High cyst concentrations of the potentially toxic dinoflagellate Alexandrium tamarense species complex in Bedford Basin,Halifax, Nova Scotia,Canada

We report a large cyst bed of the potentially toxic and bloom-forming dinoflagellate Alexandrium tamarense species complex in bottom sediments from the port of Halifax, Nova Scotia, Canada. The average cyst concentrations of that species ranged from 4033 ± 2647 to 220 872 ± 148 086 cysts g^?1 of dry sediments and the highest concentrations were found near ship terminals in Bedford Basin. Although this species is endemic to this region, our work strongly suggests that some of the cysts of A. tamarense species complex found in the port of Halifax were introduced through discharged ballast water and sediments.     

Luminescence dating of archaeosediments: A comparison of K-feldspar and plagioclase IRSL ages

IRSL single-aliquot dating of three feldspar fractions from a Howieson's Poort (SA) industry site has been investigated. In the case of the plagioclase fraction (ρ > 2.62 g cm^?3) equivalent dose is similar to that of the other fractions (i.e. ρ < 2.58 g cm^?3, high-K-feldspar; and 2.58 < ρ < 2.62 g cm^?3; low-K-feldspar). However, the g values measured for this fraction is such that the fading-corrected age is overestimated. The K content of each fraction was estimated by SEM. The DRC-corrected ages for the two lighter feldspar fractions are consistent with the archaeological interpretation. This study shows that reliable single-aliquot luminescence ages can be obtained using K-feldspar and Na-plagioclase.     

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.     

Carbon remineralization in the Amazon–Guianas tropical mobile mudbelt: A sedimentary incinerator

The Amazon River spawns a vast mobile mudbelt extending ∼1600 km from the equator to the Orinoco delta. Deposits along the Amazon–Guianas coastline are characterized by some of the highest C_org remineralization rates reported for estuarine, deltaic, or shelf deposits, however, paradoxically, except where stabilized by mangroves or intertidal algal mats, they are usually suboxic and nonsulfidic. A combination of tides, wind-driven waves, and coastal currents forms massive fluid muds and mobile surface sediment layers ∼0.5–2 m thick which are dynamically refluxed and frequently reoxidized. Overall, the seabed functions as a periodically mixed batch reactor, efficiently remineralizing organic matter in a gigantic sedimentary incinerator of global importance. Amazon River material entering the head of this dynamic dispersal system carries an initial terrestrial sedimentary C_org loading of ∼ 0.7 mg C m⁻² particle surface area. Total C_org loading is lowered to ∼ 0.2 mg C m⁻² in the proximal delta topset, ∼60–70% of which remains of terrestrial origin. Loading decreases further to 0.12–0.14 mg C m⁻² (∼60% terrestrial) in mudbanks ∼600 km downdrift along French Guiana, values comparable to those found in the oligotrophic deepsea. DOC/ΣCO₂ ratios in pore waters of French Guiana mudbanks indicate that >90% of metabolized organic substrates are completely oxidized. Within the Amazon delta topset at the head of the dispersal system, both terrestrial and marine organic matter contribute substantially to early diagenetic remineralization, although reactive marine substrate dominates (∼60–70%). The conditional rate constant for terrestrial C_org in the delta topset is ∼0.2 a⁻¹. As sedimentary C_org is depleted during transit, marine sources become virtually the exclusive substrate for remineralization except very near the mangrove shoreline. The δ¹³C and Δ¹⁴C values of pore water ΣCO₂ in mudbanks demonstrate that the primary source of remineralized organic matter within ∼1 km of shore is a small quantity of bomb signature marine plankton (+80‰). Thus, fresh marine organic material is constantly entrained into mobile deposits and increasingly drives early diagenetic reactions along the transit path. Relatively refractory terrestrial C_org is lost more slowly but steadily during sedimentary refluxing and suboxic diagenesis. Amazon Fan deposits formed during low sea level stand largely bypassed this suboxic sedimentary incinerator and stored material with up to ∼3X the modern high stand inner shelf C_org load (Keil et al., 1997b. Proceedings of the Ocean Drilling Program, Scientific Results. Vol. 155. pp. 531–537). Sedimentary dynamics, including frequency and magnitude of remobilization, and the nature of dispersal systems are clearly key controls on diagenetic processes, biogeochemical cycling, and global C storage along the continental margins.     

Ground-based Pc5 ULF wave power: Solar wind speed and MLT dependence

Using over 20 years of ground-based magnetometer data from the CANOPUS/CARISMA magnetometer array, we present a statistical characterisation of Pc5 ultra-low frequency (ULF) power in the 2–10 mHz band as a function of magnetic local time (MLT), L-shell, and solar wind speed. We examine the power across L-shells between 4.2 and 7.9, using data from the PINA, ISLL, GILL and FCHU stations, and demonstrate that there is a significant MLT dependence in both the H- and D-component median 2–10 mHz power during both fast (>500 km/s) and slow (<500 km/s) solar wind speeds. The H-component power consistently dominates over D-component power at all MLTs and during both fast and slow solar wind. At the higher-L stations (L>5.4), there are strong MLT power peaks in the morning and midnight local time sectors; the morning sector dominating midnight during fast solar wind events. At lower L-shells, there is no evidence of the midnight peak and the 2–10 mHz power is more symmetric with respect to MLT except during the fastest solar wind speeds. There is little evidence in the ground-based power of a localised MLT peak in ULF power at dusk, except at the lowest L-shell station, predominantly in the H-component. The median 2–10 mHz power increases with an approximate power law dependence on solar wind speed, at all local times across the L-shell domain studied in both components. The H-component power peaks at the latitude of the GILL station, with significantly lower power at both higher and lower L-shells. Conversely, the D-component power increases monotonically. We believe that this is evidence for 2–10 mHz power accumulating at auroral latitudes in field line resonances. Finally, we discuss how such ULF wave power characterisation might be used to derive empirical radiation belt radial diffusion coefficients based on, and driven by, the solar wind speed dependence of ULF wave power.