Koyna,India, an ideal site for near field earthquake observations

The Koyna earthquake of M 6.3 on December 10, 1967 is the largest artificial water reservoir triggered earthquake globally. It claimed ～ 200 human lives and devastated the Koyna township. Before the impoundment of the Shivaji Sagar Lake created by the Koyna Dam, there were no earthquakes reported from the region. Initially a few stations were operated in the region by the CentralWater and Power Research Station (CWPRS). The seismic station network grew with time and currently the National Geophysical Research Institute (NGRI), Hyderabad is operating 23 broadband seismographs and 6 bore hole seismic stations. Another reservoir, Warna, was created in 1985, which provided a further impetus to Reservoir Triggered Seismicity (RTS). Every year following the monsoon, water levels rise in the two reservoirs and there is an immediate increase in triggered earthquakes in the vicinity of Koyna-Warna reservoirs in the months of August–September. Peak RTS is observed in September and later during December.Another spurt in triggered earthquakes is observed during the draining of the reservoirs in the months of April- May. A comparative study of RTS earthquake sequences and the ones occurring in nearby regions made it possible to identify four common characteristics of RTS sequences that discriminate them from normal earthquake sequences. As the RTS events continue to occur at Koyna in a large number in a limited area of 20 km x 30 km, at shallow depths (mostly 2 to 9 km), the region being accessible for all possible observations and there being no other source of earthquakes within 100 km of Koyna Dam, it was suggested to be an ideal site for near field observations of earthquakes. This suggestion was discussed by the global community at an ICDP sponsored workshop held at Hyderabad and Koyna in 2011. There was an unanimous agreement about the suitability of the site for deep scientific drilling; however, a few additional observations/experiments were suggested. These were carried out in the following three years and another ICDP workshop was held in 2014, which totally supported setting up a borehole laboratory for near field investigations at Koyna. Location of a Pilot Bore-hole was decided on the basis of seismic activity and other logistics. The 3 km deep Pilot Borehole was spudded on December 20, 2016 and completed on June 11, 2017.     

Phase relations inferred from field data for mn pyroxenes and pyroxenoids

Electron microprobe analysis of manganese silicates from Balmat, N.Y., has helped elucidate phase relations for Mn-bearing pyroxenes and pyroxenoids. A compilation of these data along with published and unpublished analyses for phases plotting on the CaSiO₃-MgSiO₃-MnSiO₃ and CaSiO₃-FeSiO₃-MnSiO₃ faces of the RSiO₃ tetrahedron has constrained the subsolidus phase relations. For the system CaSiO₃-FeSiO₃-MnSiO₃, the compositional gaps between bustamite/hedenbergite, bustamite/ rhodonite and rhodonite/pyroxmangite are constrained for middle-upper amphibolite facies conditions and extensive solid solutions limit possible three phase fields. For the CaSiO₃-MgSiO₃-MnSiO₃ system much less data are available but it is clear that the solid solutions are much more limited for the pyroxenoid structures and a continuum of compositions is inferred for clinopyroxenes from diopside to kanoite (MnMgSi₂O₆) for amphibolite facies conditions (T=650° C). At lower temperatures, Balmat kanoites are unstable and exsolve into C2/c calciumrich (Ca_0.68Mn_0.44Mg_0.88Si₂O₆) and C2/c calciumpoor (Ca_0.12Mn_1.02Mg_0.86Si₂O₆) phases. At temperatures of 300–400° C the calcium-poor phase subsequently has undergone a transformation to a P2₁/c structure; this exsolution-inversion relationship is analogous to that relating augites and pigeonites in the traditional pyroxene quadrilateral. Rhodonite coexisting with Mn-clinopyroxenes is compositionally restricted to Mn_0.75–0.95Mg_0.0–0.15Ca_0.05–0.13SiO₃. For the original pyroxene+rhodonite assemblage, the Mg and Ca contents of the rhodonite are fixed for a specific P (6kbars)-T (650° C)-X(H₂O)-X(CO₂) by the coexistence of talc+quartz and calcite+quartz respectively.Contribution No. 363, from the Mineralogical Laboratory, Department of Geological Sciences, The University of Michigan, Ann Arbor MI 48109, USA     

Rare earth element transport in the western North Atlantic inferred from Nd isotopic observations

The isotopic composition of Nd in the water column from several western North Atlantic sites and formational areas for North Atlantic Deep Water shows extensive vertical structure at all locations. In regions where a thermocline is well-developed, large isotopic shifts (2 to 3 ϵ units) are observed across the base of the thermocline. Regions without a thermocline are characterized by much more gradual shifts in isotopic composition with depth. In general, the data reveal an excellent correlation between the Nd isotopic distribution in the western North Atlantic water column and the distribution of water masses identified from temperature and salinity characteristics. NADW, as identified from T-S properties, is also characterized by a well-defined isotopic composition having ϵ_Nd(0) = −13.5 ± 0.5. This signature is associated with waters identified as NADW from high latitudes near formational areas in the Labrador Sea down to the equatorial region. The isotopic signature of NADW would appear to be formed by a blend of more negative waters originating in the Labrador Sea (ϵ_Nd(0) < −18) and more positive waters originating in the overflows from the Norwegian and Greenland Seas (ϵ_Nd(0) ≈ −8 to −10) and is consistent with classical theories on the formation of NADW. The isotopic signature of NADW is propagated southward to the equator where it is gradually being thinned out by mixing from above and below with more radiogenic Nd associated with northward-spreading Antarctic Intermediate and Bottom Waters. The preservation of the isotopic signature of NADW over these large distances indicate that the REE undergo extensive lateral transport. The isotopic composition of Nd is largely conservative over the time scales of mixing within the Atlantic in spite of the intrinsic nonconservative behavior of neodymium. Nd concentration gradients generally show surface waters to be depleted in Nd relative to deep waters, which must require vertical transport processes. However, isotopic differences in the water column preclude the local downward transport of REE from the surface into underlying deep waters as a simple explanation of the concentration gradient. The apparent decoupling of REE in NADW from overlying (local) surface waters and the increasing concentration with depth provide a conflict with simple vertical transport mechanisms that is not yet resolved.     

Crustal architecture of the Thomson Orogen in Queensland inferred from potential field forward modelling

The basement rocks of the poorly understood Thomson Orogen are concealed by mid-Paleozoic to Upper Cretaceous intra-continental basins and direct information about the orogen is gleaned from sparse geological data. Constrained potential field forward modelling has been undertaken to highlight key features and resolve deeply sourced anomalies within the Thomson Orogen. The Thomson Orogen is characterised by long-wavelength and low-amplitude geophysical anomalies when compared with the northern and western Precambrian terranes of the Australian continent. Prominent NE- and NW-trending gravity anomalies reflect the fault architecture of the region. High-intensity Bouguer gravity anomalies correlate with shallow basement rocks. Bouguer gravity anomalies below –300 µm/s² define the distribution of the Devonian Adavale Basin and associated troughs. The magnetic grid shows smooth textures, punctuated by short-wavelength, high-intensity anomalies that indicate magnetic contribution at different crustal levels. It is interpreted that meta-sedimentary basement rocks of the Thomson Orogen, intersected in several drill holes, are representative of a seismically non-reflective and non-magnetic upper basement. Short-wavelength, high-intensity magnetic source bodies and colocated negative Bouguer gravity responses are interpreted to represent shallow granitic intrusions. Long-wavelength magnetic anomalies are inferred to reflect the topography of a seismically reflective and magnetic lower basement. Potential field forward modelling indicates that the Thomson Orogen might be a single terrane. We interpret that the lower basement consists of attenuated Precambrian and mafic enriched continental crust, which differs from the oceanic crust of the Lachlan Orogen further south.     

Environmental conditions in northwestern Russia during MIS 5 inferred from the pollen stratigraphy in a sediment core from Lake Ladoga

Lake Ladoga hosts preglacial sediments, although the Eurasian ice sheet overrode the area during the LGM. These sediments were first discovered by a seismic survey and are investigated using a 22.75‐m‐long core. Its upper 13.30 m comprise Holocene and Lateglacial sediments separated from the lower 11.45 m of preglacial sediments by a hiatus. They consist of highly terrigenous lacustrine sediments, which according to OSL dating, were deposited during an early stage of the last ice age (MIS 5). The palynological data allow a first reconstruction of the Early Weichselian environmental history for northwestern Russia. Birch and alder forests with broad‐leaved taxa dominated during MIS 5d (c. 118–113 ka), suggesting a climate more favourable than in the Holocene. A high content of well‐sorted sands and poorly preserved palynomorphs indicates a shallow‐water environment at least temporarily. More fine‐grained sediments and better preserved organic remains suggest deeper water environments at the core location during MIS 5c (c. 113–88 ka). Pine and spruce became dominant, while broad‐leaved taxa started to disappear, especially after c. 90 ka, pointing to a gradual climate cooling. An increase in open herb‐dominated habitats at the beginning of MIS 5b (c. 88–86 ka) reflects a colder and dryer climate. However, later (c. 86–82 ka) pine and spruce again became more common. Birch and alder forests dominated in the area c. 82–80 ka (beginning of MIS 5a). Although open treeless habitats also became more common at this time, a slight increase in hazel may point to somewhat warmer climate conditions coinciding with the beginning of MIS 5a. The studied sediments also contain numerous remains of freshwater algae and cysts of marine and brackish‐water dinoflagellates and acritarchs documenting that the present lake basin was part of a brackish‐water basin during the Early Weichselian, probably as a gulf of the Pre‐Baltic Sea.     

The osmium isotopic composition change of Cenozoic sea water as inferred from a deep-sea core corrected for meteoritic contributions

A detailed study was made of the oceanic ¹⁸⁷Os/¹⁸⁶Os variation through the Cenozoic by using a hydrogen peroxide leaching procedure on a pelagic clay core from the North Pacific (Long Lines-44 GPC3). A 6% H₂O₂ solution was used. The range of ¹⁸⁷Os/¹⁸⁶Os obtained by this procedure was between 2 and 8.2. A milder leach (0.15% H₂O₂) in three out of four samples yielded a slightly higher ¹⁸⁷Os/¹⁸⁶Os value than the stronger leach implying that the stronger leach released some meteoritic Os with ¹⁸⁷Os/¹⁸⁶Os of 1. Using published ³He concentrations in GPC3 and cosmic dust ³He and Os fluxes to deep-sea sediments, the extraterrestrial Os concentration was estimated for each core segment and subtracted to yield “corrected” values of ¹⁸⁷Os/¹⁸⁶Os. The results based on the milder leaching protocol and the ³He correction protocol yield similar values. The “corrected” ocean water ¹⁸⁷Os/¹⁸⁶Os pattern for the past 25 million years is similar to that obtained by other workers and is compatible with other results for the entire Cenozoic. The variation with time in GPC3, uniquely, provides a statigraphic signature for the Paleogene.     

Recent hydrological behavior of the East African great lakes region inferred from GRACE,satellite altimetry and rainfall observations

We have jointly analysed space gravimetry data from the GRACE space mission, satellite altimetry data and precipitation over the East African Great Lakes region, in order to study the spatiotemporal variability of hydrological parameters (total water storage, lake water volume and rainfall). We find that terrestrial water storage (TWS) from GRACE and precipitation display a common mode of variability at interannual time scale, with a minimum in late 2005, followed by a rise in 2006–2007. We argue that this event is due to forcing by the strong 2006 Indian Ocean Dipole (IOD) on East African rainfall. We also show that GRACE TWS is linked to the El Niño-Southern Oscillation cycle. Combination of the altimetry-based lake water volume with TWS from GRACE over the lakes drainage basins allows estimating soil moisture and groundwater volume variations. Comparison with the WGHM hydrological model outputs is performed and discussed.     

Aerosol pollution and its impact on regional climate during Holi festival inferred from ground-based and satellite remote sensing observations

In this paper, we report some salient features from a suit of special experiments that have been conducted over a coastal site (Mumbai) during February 23–March 03, 2010, encompassing an Indian festival, namely Holi, using solar radiometers and pyranometer. The results of the analysis of observations at the experimental site show higher (more than double) aerosol optical depth, water vapor, and lower down-welling short-wave radiative flux during the festival period. This is considered to be due to anthropogenic activities and associated meteorological conditions at the experimental location. To illustrate further, Angstrom parameters (alpha, denoting the aerosol size distribution, and beta, representing the loading) are examined. These parameters are found to be greater on Holi day as compared to those on the normal (control, pre-, and post-Holi) days, suggesting an increase in accumulation mode (smaller size) particle loading. The aerosol size spectra exhibited bimodal/power-law distribution with a dominant peak, modulated by anthropogenic activities, involving local and long-range transport of dust and smoke (emanated from biomass-burning) aerosols, which is consistent with MODIS satellite observations. The aerosol direct radiative forcing estimation indicated cooling at the bottom of the atmosphere.     

Plate subduction,and generation of earthquakes and magmas in Japan as inferred from seismic observations: An overview

A dense nationwide seismic network recently constructed in Japan has been yielding large volumes of high-quality data that have made it possible to investigate the seismic structure in the Japanese subduction zone with unprecedented resolution. In this article, recent studies on the subduction of the Philippine Sea and Pacific plates beneath the Japanese Islands and the mechanism of earthquake and magma generation associated with plate subduction are reviewed. Seismic tomographic studies have shown that the Philippine Sea plate subducting beneath southwest Japan is continuous throughout the entire region, from Kanto to Kyushu, without disruption or splitting even beneath the Izu Peninsula as suggested in the past. The contact of the Philippine Sea plate with the Pacific plate subducting below has been found to cause anomalously deep interplate and intraslab earthquake activity in Kanto. Detailed waveform inversion studies have revealed that the asperity model is applicable to interplate earthquakes. Analyses of dense seismic and GPS network data have confirmed the existence of episodic slow slip accompanied in many instances by low-frequency tremors/earthquakes on the plate interface, which are inferred to play an important role in stress loading at asperities. High-resolution studies of the spatial variation of intraslab seismicity and the seismic velocity structure of the slab crust strongly support the dehydration embrittlement hypothesis for the generation of intraslab earthquakes. Seismic tomography studies have shown that water released by dehydration of the slab and secondary convection in the mantle wedge, mechanically induced by slab subduction, are responsible for magma generation in the Japanese islands. Water of slab origin is also inferred to be responsible for large anelastic local deformation of the arc crust leading to inland crustal earthquakes that return the arc crust to a state of spatially uniform deformation.     

Angles between the rotational axis and magnetic moment in 80 pulsars from observations near 1 GHz

Data on the pulse structure and variations of the linear polarization angle at frequencies near 1 GHz have been used to estimate the angles β between the rotational axis and magnetic moment of the neutron stars assocaited with 80 pulsars. The calculations applied several methods. The minimum values of β were estimated from the observed pulse width W ₁₀ at the 10% level for the entire sample. Maximum estimates of β were obtained for six sources with small polarization position angle derivatives. Equations for the angle β were derived for various forms of the observed profile, and solutions obtained for 34 pulsars. The β values calculated using different methods are compared. For three pulsars with known interpulses, the obtained values of β demonstrate that two (PSR B1055-52 and PSR 1822-09) are aligned rotators, whereas the other (PSR B1702-19) is an orthogonal rotator. A search for interpulses and interpulse emission in PSRB1641-45, PSR1642-03, and PSR 1944+17 is necessary, and a search for an interpulse at 180° from the main pulse is required in PSR B2321-61.     

Source complexity of the 4 March 2010 Jiashian,Taiwan, Earthquake determined by joint inversion of teleseismic and near field data

The Jiashian earthquake (M_L 6.4) occurred on 4 March 2010. It was the largest inland event in southern Taiwan of 2010. The mainshock location was unexpected since it occurred in an area with relatively low background seismicity. In addition, reports of earthquake focal mechanisms do not fit with any known active fault geometry. In order to understand the origin of this earthquake, especially its rupture process, we perform a joint source inversion by using teleseismic body wave, GPS coseismic displacements and near field ground motion data. In this study, we considered a northwest–southeast trending fault with a northeast dip retrieved from GPS coseismic data and aftershocks distribution. To analyze the detailed slip distribution in space and time, we used near field 3D Green’s functions provided by spectral-element method and a full time–space inversion technique. We find a complex rupture process with several slip patches distributed inside two main asperities. The slip map reveals a mean slip of 12.9 cm for a maximum slip of 27.3 cm leading to a M_w 6.47 for this event. The rupture initiates in the deepest portion of the fault at 20 km depth, and propagated upward up to 2 km depth to form the two asperities. The source time function of this event revealed two pulses corresponding to the two asperities, for a total duration time of about 16 s. Most aftershocks occurred near the upper boundary of the deepest asperity while no aftershocks are located close to the shallowest one. We infer that the locations of these slip patches are related to the surrounding fault systems that may have restricted the rupture propagation during the earthquake.     

Glacial and Holocene terrestrial temperature variability in subtropical east Australia as inferred from branched GDGT distributions in a sediment core from Lake McKenzie

Branched glycerol dialkyl glycerol tetraether (GDGT) distributions observed in a sediment core from Lake McKenzie were utilized to quantitatively reconstruct the pattern of mean annual air temperature (MAAT) from coastal subtropical eastern Australia between 37 and 18.3 cal ka BP and 14.0 cal ka BP to present. Both the reconstructed trend and amplitude of MAAT changes from the top of the sediment core were nearly identical to a local instrumental MAAT record from Fraser Island, providing confidence that in this sediment core branched GDGTs could be used to produce a quantitative record of past MAAT. The reconstructed trend of MAAT during 37 to 18.3 cal ka BP and timing of the Last Glacial Maximum (LGM) in the Lake McKenzie record were in agreement with previously published nearby marine climate records. The amplitude of lower-than-present MAAT during the LGM potentially provides information on the latitude of separation of the Tasman Front from the East Australian current in the subtropical western Pacific. The Lake McKenzie record shows an earlier onset of near modern day warm temperatures in the early Holocene compared to marine records and the presence of a warmer than present day period during the mid-Holocene.     

Site response of the Ganges basin inferred from re-evaluated macroseismic observations from the 1897 Shillong, 1905 Kangra,and 1934 Nepal earthquakes

We analyze previously published geodetic data and intensity values for the M _s = 8.1 Shillong (1897), M _s = 7.8 Kangra (1905), and M _s = 8.2 Nepal/Bihar (1934) earthquakes to investigate the rupture zones of these earthquakes as well as the amplification of ground motions throughout the Punjab, Ganges and Brahmaputra valleys. For each earthquake we subtract the observed MSK intensities from a synthetic intensity derived from an inferred planar rupture model of the earthquake, combined with an attenuation function derived from instrumentally recorded earthquakes. The resulting residuals are contoured to identify regions of anomalous intensity caused primarily by local site effects. Observations indicative of liquefaction are treated separately from other indications of shaking severity lest they inflate inferred residual shaking estimates. Despite this precaution we find that intensites are 1–3 units higher near the major rivers, as well as at the edges of the Ganges basin. We find evidence for a post-critical Moho reflection from the 1897 and 1905 earthquakes that raises intensities 1–2 units at distances of the order of 150 km from the rupture zone, and we find that the 1905 earthquake triggered a substantial subsequent earthquake at Dehra Dun, at a distance of approximately 150 km. Four or more M = 8 earthquakes are apparently overdue in the region based on seismic moment summation in the past 500 years. Results from the current study permit anticipated intensities in these future earthquakes to be refined to incorporate site effects derived from dense macroseismic data.     

Earthquake hazard assessment from the recent space and surface measurements of the Earth's gravity field

The distinctive nature of the structure of the Earth's gravity field over high seismicity areas, as observed in some limited scale studies, indicates that it is possible to use these associative patterns to outline areas of high seismicity or high earthquake hazard potential from a knowledge of the finer structure of the Earth's gravity field. The global scale investigation of such relationships as a function of the geophysical characteristics of various tectonic provinces, and the parameterisation of such relationships by hypocentral depth and earthquake intensity/energy data, become even more attractive because of the availability of (1) satellite-determined gravity models which provide global information on the long wavelength components of the gravity field, (2) satellite altimetry data which provide oceanwide information on the detailed geoidal structure, (3) surface gravity data which provide information on the short wavelength components in the areas of surface gravity coverage, and (4) bathymetric and topographic data which, though still somewhat limited in spite of their recent extensions of coverage, are available in more and more areas and provide information on the tectonic and morphological environments of an area to enable its gravity data conversion to some standard environments for direct comparisons of underlying structures. Additionally, the rapidly mounting geological and geophysical evidence of considerable intraplate tectonic activity, not so fashionable until recently, makes the study of these correlative patterns even more attractive and productive from a scientific viewpoint. This paper presents the major elements of the theoretical formulation for conducting such investigations.     

Annual phytoplankton metabolism in Narragansett Bay calculated from survey field measurements and microcosm observations

Field surveys of phytoplankton metabolism, based on oxygen changes, were made in Narragansett Bay from 1971–73. Annual daytime net production varied from 218 g C per m² per yr in the East Passage to 429 g C per m² per yr in the Providence River. The area based average for the bay was 269 g C per m² per yr. The area based average night respiration was 159 g C per m² per yr resulting in an annual net carbon available for export or to the benthos of 110 g C per m² per yr. A set of microcosms, operated so as to simulate the Bay, had an annual net production of 276 g C per m² per yr and a night respiration of 163 g C per m² per yr resulting in an annual net carbon available for export or to the benthos of 113 g C per m² per yr. *** DIRECT SUPPORT *** A01BY015 00002     

浅谈野外岩心地质编录工作

岩心地质编录是收集和观察研究岩心中所赋存的各种地质信息和地质现象的一项重要的基础性地质工作。本文根据具体实践经验，简要介绍了岩心地质编录工作的3个阶段以及贯穿于编录工作始终的取样工作。     

Formation of the Eurasia Basin in the Arctic Ocean as inferred from geohistorical analysis of the anomalous magnetic field

A new combined magnetic database and a magnetic-profile map are developed for the Eurasia Basin as a result of adjusting all available historical and recent Russian and American magnetic data sets. The geohistorical analysis of magnetic data includes several steps: identification of linear magnetic anomalies along each trackline, calculation of the Euler rotation pole positions for the relative motion of the North American and Eurasian plates, analysis of temporal and spatial variations in the spreading rate, and plate reconstructions. The pattern of key Cenozoic magnetic isochrons (24, 20, 18, 13, 6, 5, 2a) is constructed for the entire Eurasia Basin. In the western half of the basin, this pattern is consistent with a recently published scheme [16]. In its eastern half, magnetic isochrons are determined in detail for the first time and traced up to the Laptev Sea shelf. The main stages in the seafloor spreading are established for the Eurasia Basin. Each stage is characterized by a specific spreading rate and the degree of asymmetry of the basin opening. The revealed differences are traced along the Gakkel Ridge. Systematic patterns in wandering of the Eurasia Basin opening pole are established for particular stages. The continent-ocean transition zone corresponding to the primary rupture between plates is outlined in the region under consideration on the basis of gravimetric data. The nature of different potential fields and bottom topography on opposite sides of the Gakkel Ridge is discussed. The characteristic features of the basin-bottom formation at main stages of its evolution are specified on the basis of new and recently published data. The results obtained are in good agreement with plate geodynamics of the North Atlantic and the adjacent Arctic basins.     

Evidence of Quaternary active folding near Utique (Northeast Tunisia) from tectonic observations and a seismic profile

The present-day seismicity in northeastern Tunisia reported from permanent networks is of low to moderate magnitude. However, earthquakes are mentioned in the literature, specially a destructive one in the antique city of Utique. Geologic, seismic, and neotectonic investigations in this area show that the Utique fold is closely related to the recent tectonic activity in this region. Data show that the Utique fold is built on an east-west fault, and we found evidence of activity of this fault in the past 20 kyr. A seismic section and balanced cross-section show that the slip rate is of the order of 0.38 mm.yr⁻¹. Our data show definitively the Late Pleistocene–Holocene activity of the Utique Fault; and we can predict the earthquake recurrence interval which should be of ∼10³–10⁴ yr. This high seismic risk zone deserves to be taken into account during the establishment of important regional development programs and in the application of seismic building codes.