Paleomagnetism of the Late Cretaceous ignimbrite from the Okhotsk-Chukotka Volcanic Belt,Kolyma-Omolon Composite Terrane: Tectonic implications

New Late Cretaceous paleomagnetic results from the Okhotsk-Chukotka Volcanic Belt in the Kolyma-Omolon Composite Terrane yield stable and consistent remanent directions. The Late Cretaceous (86–81 Ma) ignimbrites from the Kholchan and Ola suites were sampled at 19 sites in the Magadan area (60.4° N, 151.0° E). We isolated the characteristic paleomagnetic directions from 16 sampled sites using an alternating field demagnetization procedure. The primary nature of these directions is ascertained by dual polarities and positive fold tests. A tilt-corrected mean direction (D = 42.8°, I = 84.7°, k = 46.0, α₉₅ = 10.0°) yields a paleomagnetic pole of 66.7° N, 168.5° E (A₉₅ = 18.8°) which appears almost identical to the 90–67 Ma pole reported from the Lake El’gygytgyn area of the Okhotsk-Chukotka Volcanic Belt (Chukotka Terrane). This consistency suggests that the Kolyma-Omolon Composite Terrane and Chukotka Terrane has acted as a single tectonic unit since 80 Ma without any significant internal deformation. Accordingly, we calculate a combined 80 Ma characteristic paleomagnetic pole (Long. = 164.7° E, Lat. = 68.0°, A₉₅ = 10.9°, N = 12) for the Kolyma-Omolon-Chukotka Block which falls 16.5–17.5° south of the same age poles from Europe and East Asia. We ascribe this discrepancy in pole positions to tectonic activity in the area and infer a southward displacement of 1640 ± 1380 km for the Kolyma-Omolon-Chukotka Block with respect to the North American and Eurasian blocks since 80 Ma; more than 260 km of it is attributed to tectonic displacement in the Arctic Ocean due to the opening of the Canadian Basin.     

Whistlers observed at low-latitude ground-based VLF facility in Fiji

The propagation features of nighttime whistlers to low-latitude station, Suva (−18.2°, 178.3°, geomag. lat. −22.1°, geomag. long. 253.5°, L=1.15), Fiji, from preliminary observations made during the period from September 2003–2005, are reported. The observations of ELF–VLF signals commenced in September 2003 using the VLF set-up of World Wide Lightning Location Network at our station. The whistlers were observed during the severe magnetic storm of 20–22 November 2003 and moderate magnetic storm of 17–19 July 2005. A whistler with dispersion D=12.7 s^1/2 occurred on 22 November at 00:11 h LT. On 20 July at 01:00 h LT, a short whistler with dispersion D=20.9 s^1/2 and two whistler events having two-component whistlers with D=15.8, 16.7 s^1/2 and 16.7, 17.3 s^1/2 were observed. Non-ducted pro-longitudinal mode of the whistler propagation supported by negative latitudinal electron density gradients in the ionosphere that are enhanced by magnetic storms, seems most likely mode of propagation for the whistlers with dispersion of 12.7–17.3 s^1/2 to this low-latitude station.     

Paleomagnetic results from Late Carboniferous to Early Permian rocks in the northern Qiangtang terrane,Tibet, China,and their tectonic implications

Results of a systematic paleomagnetic study are reported based on Late Carboniferous to Early Permian sedimentary rocks on the north slope of the Tanggula Mountains,in the northern Qiangtang terrane(NQT),Tibet,China.Data revealed that magnetic minerals in limestone samples from the Zarigen Formation(CP^z)are primarily composed of magnetite,while those in sandstone samples from the Nuoribagaribao Formation(Pnr)are dominated by hematite alone,or hematite and magnetite in combination.Progressive thermal,or alternating field,demagnetization allowed us to isolate a stable high temperature component(HTC)in 127 specimens from 16 sites which successfully passed the conglomerate test,consistent with primary remnance.The tilt-corrected mean direction for Late Carboniferous to Early Permian rocks in the northern Qiangtang terrane is D_s=30.2°,I_s=-40.9°,k_s=269.0,a_(95)=2.3°,N=16,which yields a corresponding paleomagnetic pole at 25.7°N,241.5°E(dp/dm=2.8°/1.7°),and a paleolatitude of 23.4°S.Our results,together with previously reported paleomagnetic data,indicate that:(1)the NQT in Tibet,China,was located at a low latitude in the southern hemisphere,and may have belonged to the northern margin of Gondwana during the Late Carboniferous to Early Permian;(2)the Paleo-Tethys Ocean was large during the Late Carboniferous to Early Permian,and(3)the NQT subsequently moved rapidly northwards,perhaps related to the fact that the Paleo-Tethys Ocean was rapidly contracting from the Late Permian to Late Triassic while the Bangong Lake-Nujiang Ocean,the northern branch of the Neo-Tethys Ocean,expanded rapidly during this time.     

Paleomagnetic dating of Phanerozoic kimberlites in Siberia

Diamond bearing kimberlite pipes are exposed across the north-central part of the Siberian platform. Three main time intervals are considered to be the age of emplacement: the Devonian–Early Carboniferous, Triassic, and Cretaceous. However, isotopic age data from of the pipes are scattered and provide a very broad age interval for the magmatic activity. New paleomagnetic poles from four kimberlite pipes (Eastern Udachnaya, Western Udachnaya, International and Obnazhennaya) are obtained to estimate their paleomagnetic age. The mean primary magnetization directions for the pipes are as follows: D = 4.3°, I = − 44.5° (k = 29.4, α₉₅ = 7.4°, N = 14); D = 340.5°, I = − 65.6° (k = 12.9, α₉₅ = 19.4°, N = 6); D = 291.1°, I = − 78.1° (k = 27.5, α₉₅ = 14.9°, N = 5); and D = 306.7°, I = − 82.6° (k = 38.4, α₉₅ = 5.8°, N = 17), respectively. On the basis of a comparison with the Siberian apparent polar wander path (APWP) we estimate the age of kimberlite magmatism, assuming primary magnetizations in these rocks. The paleomagnetic ages are as follows: 428 ± 13 Ma for Eastern Udachnaya; 251 ± 30 Ma for International pipe; and 168 ± 11 Ma for Obnazhennaya pipe. The Western Udachnaya pipe was remagnetized and no clear paleomagnetic age could be determined. The ages of magmatic activity span the Early Silurian to Middle Late Jurassic. Early Silurian magmatism could be associated with the formation of the Viluy rift. Middle to Late Jurassic magmatic activity is most likely related to subduction related to the accretion of surrounding terranes to Siberia.     

On the comparison of tidal gravity parameters with tidal models in central Europe

Two accurately calibrated superconducting gravimeters (SGs) provide high quality tidal gravity records in three central European stations: C025 in Vienna and at Conrad observatory (A) and OSG050 in Pecný (CZ). To correct the tidal gravity factors from ocean loading effects we compared the load vectors from different ocean tides models (OTMs) computed with different software: OLFG/OLMP by the Free Ocean Tides Loading Provider (FLP), ICET and NLOADF. Even with the recent OTMs the mass conservation is critical but the methods used to correct the mass imbalance agree within 0.1 nm/s². Although the different software agrees, FLP probably provides more accurate computations as this software has been optimised. For our final computation we used the mean load vector computed by FLP for 8 OTMs (CSR4, NAO99, GOT00, TPX07, FES04, DTU10, EOT11a and HAMTIDE). The corrected tidal factors of the 3 stations agree better than 0.04% in amplitude and 0.02° in phase. Considering the weighted mean of the three stations we get for O1 δ_c = 1.1535 ± 0.0001, for K1 δ_c = 1.1352 ± 0.0003 and for M2 δ_c = 1.1621 ± 0.0003. These values confirm previous ones obtained with 16 European stations. The theoretical body tides model DDW99/NH provides the best agreement for M2 (1.1620) and MATH01/NH for O1 (1.1540) and K1 (1.1350). The largest discrepancy is for O1 (0.05%). The corrected phase α_c does not differ significantly from zero except for K1 and S2. The calibrations of the two SG's are consistent within 0.025% and agree with Strasbourg results within 0.05%.     

New paleomagnetic constraints on the late Cretaceous and early Cenozoic tectonic history of the Eastern Pontides

The Pontides are characterized by a series of Mesozoic-Cenozoic fold belts comprising a N-vergent foreland fold and thrust belt in the Western Pontides and a concave, upward-shaped fold belt in the Eastern Pontides. The curvature of the fold belt follows the Caucasus which may imply a phase of oroclinal bending. In order to test whether the fold curvature represents a phase of oroclinal bending, a paleomagnetic study has been carried out in the Eastern Pontides on late Cretaceous and middle Eocene volcanic and sedimentary rocks from 29 sites. Rock magnetic studies reveal medium-temperature components with an unblocking temperature of 400–580 °C, indicating pseudo-single domain titanomagnetite as the most abundant carrier of magnetic remanence in the middle Eocene rocks studied here. In the upper Cretaceous rocks, a high-temperature component with an unblocking range of 580–650 °C was isolated. Stepwise thermal and alternating field demagnetization isolated two components of remanent magnetization in middle Eocene rocks comprising a low unblocking temperature/coercivity component near the present field direction and a characteristic remanent magnetization (ChRM) component of D_s = 332.3°, I_s = 49.9° (k = 33.3, α₉₅ = 9.2°, N = 15 sites). A positive fold test at a 95% confidence level and a reversal test indicate a primary magnetization. Component analysis of the upper Cretaceous rocks identifies a stable ChRM D_s = 160.3°, I_s = −45.0°, (k =  85.6, α₉₅ = 6.0°, N =  8 sites) following removal of secondary remanence. Their ChRM direction passes fold and reversal tests at a 95% confidence level. Both the upper Cretaceous and middle Eocene paleomagnetic data from the Eastern Pontides and the Lesser Caucasus clearly demonstrate evidence of oroclinal bending that occurred contemporaneouslywith the convergence between Arabia and Eurasia in the Paleocene.     

Coda-Q and its lapse time dependence analysis in the interaction zone of the Dinarides,the Alps and the Pannonian basin

The single backscattering model was used to estimate total attenuation of coda waves (Q_c) of local earthquakes recorded on eight seismological stations in the complex area of the western continental Croatia. We estimated Q₀ and n, parameters of the frequency dependent coda-Q using the relation Q_c = Q₀fⁿ. Lapse time dependence of these parameters was studied using a constant 30 s long time window that was slid along the coda of seismograms. Obtained Q_c were distributed into classes according to their lapse time, t_L. For t_L = 20–50 s we estimated Q₀ = 45–184 and n = 0.49–0.94, and for t_L = 60–100 s we obtained Q₀ = 119–316 and n = 0.37–0.82. There is a tendency of decrease of parameter n with increasing Q₀, and vice versa. The rates of change of both Q₀ and n seem to decrease for lapse times larger than 50–80 s, indicating an alteration in rock properties controlling coda attenuation at depths of about 100–160 km. A very good correlation was found between the frequency dependence parameter n and the Moho depths for lapse times of 50, 60 and 70 s.     

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).     

Characterization of the crust of the Coast Mountains Batholith,British Columbia,from P to S converted seismic waves and petrologic modeling

The late Triassic to early Tertiary Coast Mountains Batholith (CMB) of British Columbia provides an ideal locale to study the processes whereby accreted terranes and subduction-related melts interact to form stable continental crust of intermediate to felsic composition and complementary ultramafic residuals. Seismic measurements, combined with calculated elastic properties of various CMB rock compositions, provide a window into the deep-crustal lithologies that are key to understanding the processes of continental growth and evolution. We use a combination of seismic observations and petrologic modeling to construct hypothetical crustal sections at representative locations across the CMB, then test the viability of these sections via forward modeling with synthetic seismic data. The compositions that make up our petrologic forward models are based on calculations using the free energy minimization program Perple_X to predict mineral assemblages at depth for the bulk compositions of exposed plutonic rocks collected in the study area. Seismic data were collected along two transects in west-central British Columbia: a southern line that crossed the CMB near the town of Bella Coola (near 52° N), and a northern line centered on the towns of Terrace and Kitimat (near 54° N). Along both transects, seismic receiver functions reveal high V_p/V_s ratios near the Insular/Intermontane terrane boundary and crustal thickness increasing from 26 ± 3 km to 34 ± 3 km (at the 1 sigma certainty level) from west to east across the Coast Shear Zone (CSZ). On the southern line, we observe an anomalous region of complex receiver functions and diminished Moho signals beneath the central portion of the CMB. Our petrologic and seismic profiles show that observed seismic data from much of the CMB can be well-matched in terms of crustal thickness and structure, average V_p/V_s, and amplitude of the Moho converted phase, without including ultramafic residual material in the lower crust.     

An evaluation of methods for determining during-storm precipitation phase and the rain/snow transition elevation at the surface in a mountain basin

Determining surface precipitation phase is required to properly correct precipitation gage data for wind effects, to determine the hydrologic response to a precipitation event, and for hydrologic modeling when rain will be treated differently from snow. In this paper we present a comparison of several methods for determining precipitation phase using 12 years of hourly precipitation, weather and snow data from a long-term measurement site at Reynolds Mountain East (RME), a headwater catchment within the Reynolds Creek Experimental Watershed (RCEW), in the Owyhee Mountains of Idaho, USA. Methods are based on thresholds of (1) air temperature (T_a) at 0 °C, (2) dual T_a threshold, −1 to 3 °C, (3) dewpoint temperature (T_d) at 0 °C, and (4) wet bulb temperature (T_w) at 0 °C. The comparison shows that at the RME Grove site, the dual threshold approach predicts too much snow, while T_a, T_d and T_w are generally similar predicting equivalent snow volumes over the 12 year-period indicating that during storms the cloud level is at or close to the surface at this location. To scale up the evaluation of these methods we evaluate them across a 380 m elevation range in RCEW during a large mixed-phase storm event. The event began as snow at all elevations and over the course of 4 h transitioned to rain at the lowest through highest elevations. Using 15-minute measurements of precipitation, changes in snow depth (z_s), T_a, T_d and T_w, at seven sites through this elevation range, we found precipitation phase linked to the during-storm surface humidity. By measuring humidity along an elevation gradient during the storm we are able to track changes in T_d to reliably estimate precipitation phase and effectively track the elevation of the rain/snow transition during the event.     

Enhancement of OI 630.0 nm emission at mid-latitudes during an intense magnetic storm

All-sky camera (ASC), Global Positioning System (GPS), and ionosonde measurements were used to investigate the upper atmospheric variations at mid-latitude during the strong geomagnetic storm on October 29–31, 2003. An arc-shaped 630.0 nm emission was observed in the northern sky on all-sky images taken at Mt. Bohyun (36.2°N, 128.9°E, GMLAT=29°N) in Korea during 17:48–8:58 UT in the main phase of the geomagnetic storm on October 29. The NmF₂ and hmF₂ from the ionosonde show strong disturbances at that time. The vertical profiles of electron densities, calculated by the ionospheric tomographic method using ground-based GPS slant total electron contents measurements, show the largest value at ∼440 km height at 18:30 UT on October 29 when the enhancements of OI 630.0 nm emission were observed. The arc-shaped red emission observed during the main phase of the magnetic storm is likely a low-latitude red aurora due to its short duration of ∼1 h. The result implies that the plasmapause was at L=1.4–1.6 during the geomagnetic storm. The fact that the arc did not follow a constant L-value appears to suggest that neutral precipitation and a traveling ionospheric disturbance could also be the cause of the arc.     

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.     

Co-sequestration of SO2 with supercritical CO2 in carbonates: An experimental study of capillary trapping,relative permeability,and capillary pressure

In this study we performed three categories of steady- and unsteady-state core-flooding experiments to investigate capillary trapping, relative permeability, and capillary pressure, in a scCO₂ + SO₂/brine/limestone system at elevated temperature and pressure conditions, i.e., 60 °C and 19.16 MPa. We used a Madison limestone core sample acquired from the Rock Springs Uplift in southwest Wyoming. We carried out two sets of steady-state drainage-imbibition relative permeability experiments with different initial brine saturations to study hysteresis. We found that the final scCO₂ + SO₂ drainage relative permeability was very low, i.e., 0.04. We also observed a rapid reduction in the scCO₂-rich phase imbibition relative permeability curve, which resulted in a high residual trapping. The results showed that between 62.8% and more than 76% of the initial scCO₂ + SO₂ at the end of drainage was trapped by capillary trapping mechanism (trapping efficiency). We found that at higher initial brine saturations, the trapping efficiency was higher. The maximum initial and residual scCO₂-rich phase saturations at the end of primary drainage and imbibition were 0.525 and 0.329, respectively. Each drainage-imbibition cycle was followed by a dissolution process to re-establish S_w = 1. The dissolution brine relative permeabilities for both cycles were also obtained. We characterized the scCO₂ + SO₂/brine capillary pressure hysteresis behavior through unsteady-state primary drainage, imbibition, and secondary drainage experiments. We observed negative imbibition capillary pressure curve indicative of possible wettability alteration throughout the experiments due to contact with scCO₂ + SO₂/brine fluid system. The trapping results were compared to those reported in literature for other carbonate core samples. We noticed slightly more residual trapping in our sample, which might be attributed to heterogeneity, different viscosity ratio, and pore-space topologies. The impact of dynamic effects, i.e., high brine flow rate imbibition tests, on trapping of the scCO₂-rich phase was also explored. We performed two imbibition experiments with relatively high brine flow rates. The residual scCO₂ saturation dropped to 0.291 and 0.262 at the end of the first and second imbibition tests, i.e., 11.5% and 20.4%, respectively, compared to 0.329 under capillary-dominated regime.     

Evapotranspiration in the Pampean Region using field measurements and satellite data

Evapotranspiration (LE) is an important factor for monitoring crops, water requirements, and water consumption at local and regional scale. In this paper, we applied the semi-empirical model to estimate the daily latent heat flux (LE_d = Rn_d + A − B(Ts − Ta)). LE_d has been estimated using satellite images (Thematic Mapper sensor) and a local dataset (incoming and outgoing short- and long-wave radiation) measured during three years. We first estimated the daily net Radiation (Rn_d) from a linear equation derived from the instantaneous net Radiation (Rn_d = CRn_i + D). Subsequently, coefficients A and B have been estimated for two different cover vegetations (pasture and soybean). For each vegetation cover, an error analysis combining Rn_d, A, B, and surface and air temperatures has been calculated. Results showed that Rn_d had good performance (nonbias and low RMSE). LE_d errors for pasture and soybean were ±28 W m⁻² and ±40 W m⁻² respectively.     

Immune responses to combined effect of hypoxia and high temperature in the green-lipped mussel Perna viridis

Flow cytometry was used to examine immune responses in haemocytes of the green-lipped mussel Perna viridis under six combinations of oxygen level (1.5 mg O₂ l⁻¹, 6.0 mg O₂ l⁻¹) and temperature (20 °C, 25 °C and 30 °C) at 24 h, 48 h, 96 h and 168 h. The mussels were then transferred to normoxic condition (6.0 mg O₂ l⁻¹) at 20 °C for further 24 h to study their recovery from the combined hypoxic and temperature stress. Esterase (Est), reactive oxygen species (ROS), lysosome content (Lyso) and phagocytosis (Pha) were reduced at high temperatures, whereas hypoxia resulted in higher haemocyte mortality (HM) and reduced phagocytosis. For HM and Pha, changes were observed after being exposed to the stresses for 96 h, whereas only a 24 h period was required for ROS and Lyso, and a 48 h one for Est. Recovery from the stresses was observed for HM and Pha but not other immune responses.     

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.     

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.     

Spatial distribution and ecology of the Recent Ostracoda from Tangra Yumco and adjacent waters on the southern Tibetan Plateau: A key to palaeoenvironmental reconstruction

We elucidate the ecology of Recent Ostracoda from a deep brackish lake, Tangra Yumco (30°45′—31°22′N and 86°23′—86°49′E, 4595 m a.s.l.) and adjacent waters on the southern Tibetan Plateau. Ostracod associations (living and empty valves) in sixty-six sediment samples collected from diverse aquatic habitats (lakes, estuary-like water and lagoon-like water waters, rivers, ponds and springs) were quantitatively assessed.Eleven Recent Ostracoda were found (nine living and two as empty valves only). Cluster analysis established two significant (p < 0.05) habitat specific associations; (i) Leucocytherella sinensis, Limnocythere inopinata, Leucocythere? dorsotuberosa, Fabaeformiscandona gyirongensis and Candona xizangensis are lacustrine fauna. (ii) Tonnacypris gyirongensis, Candona candida, Ilyocypris sp., Heterocypris incongruens and Heterocypris salina are temporary water species.Ostracod distribution and abundance are significantly (p < 0.05) correlated to physico-chemical variables. The first two axes of a canonical correspondence analysis (CCA) explain 30.9% of the variation in the species abundance data. Conductivity and habitat types are the most influential ecological factors explaining the presence and abundance of ostracods. Spearman correlation analysis reveals that: (i) Two species, L.? dorsotuberosa (r = 0.25) and L. inopinata (r = 0.36) have a significant positive correlation with conductivity while one species, T. gyirongensis (r = −0.68) displays a significant negative correlation with conductivity. Limnocythere inopinata correlates significantly positive (r = 0.37) with alkalinity. Fabaeformiscandona gyirongensis correlates significantly positive (r = 0.28) with water depth.Key indicator living assemblages are: (i) L. sinensis dominates Ca-depleted brackish waters although ubiquitously distributed; (ii) L.? dorsotuberosa dwells in fresh to brackish waters; (iii) L. inopinata predominates in mesohaline to polyhaline waters; (iv) F. gyirongensis inhabits exclusively brackish-lacustrine deeper waters; (v) C. candida populates freshwaters; (vi) T. gyirongensis and Ilyocypris sp. are restricted to shallow temporary waters; (vii) H. incongruens occurs in ponds.Water depth indicators are F. gyirongensis and L.? dorsotuberosa, useful in ostracod assemblages for palaeo-water depth reconstruction.Our results expand the knowledge of the ecological significance of Recent Tibetan Ostracoda ecology. This is a new insight on habitat chacteristics of both living assemblages and sub-Recent associations of ostracods in mountain aquatic ecosystems. The new modern ostracod dataset can be used for the quantitative reconstruction of past environmental variables (e.g., conductivity) and types of water environment. The key indicator ostracods are relevant in palaeolimnological and climate research on the Tibetan Plateau.     

Geo-center movement caused by huge earthquakes

In this study we investigate co-seismic geo-center change based on a dislocation theory for a spherically symmetric, non-rotating, perfectly elastic and isotropic model. We first introduce the basic theory with emphasis on the dislocation Love numbers of degree 1, and then we present methods for computing co-seismic geo-center movement. It is found that the geo-center change reaches maximum value when δ = 45° and λ = 90°, i.e., a 45° declined dip fault causes the maximum geo-center movement. As an application, we apply the methods to compute the geo-center movement caused by the 2004 Sumatra earthquake (Mw9.3) and the 2011 Tohoku-Oki earthquake (Mw9.0). Results show that the maximum co-seismic geo-center movements for the two events are 0.87 mm and 0.43 mm, respectively.