Relationship of Tsunami Intensity to Source Earthquake Magnitude as Retrieved from Historical Data

Operational prediction of near-field tsunamis in all existing Tsunami Warning Systems (TWSs) is based on fast determination of the position and size of submarine earthquakes. Exceedance of earthquake magnitude above some established threshold value, which can vary over different tsunamigenic zones, results in issuing a warning signal. Usually, a warning message has several (from 2 to 5) grades reflecting the degree of tsunami danger and sometimes contains expected wave heights at the coast. Current operational methodology is based on two main assumptions: (1) submarine earthquakes above some threshold magnitude can generate dangerous tsunamis and (2) the height of a resultant tsunami is, in general, proportional to the earthquake magnitude. While both assumptions are physically reasonable and generally correct, statistics of issued warnings are far from being satisfactory. For the last 55 years, up to 75% of warnings for regional tsunamis have turned out to be false, while each TWS has had at least a few cases of missing dangerous tsunamis. This paper presents the results of investigating the actual dependence of tsunami intensity on earthquake magnitude as it can be retrieved from historical observations and discusses the degree of correspondence of the above assumptions to real observations. Tsunami intensity, based on the Soloviev-Imamura scale is used as a measure of tsunami “size”. Its correlation with the M _s and M _w magnitudes is investigated based on historical data available for the instrumental period of observations (from 1900 to present).     

Methodology of the indirect temperature estimation basing on magnetotelluric data: Northern Tien Shan case study

Electrical conductivity of rocks being closely related to their temperature could serve as a proxy parameter to be used for indirect temperature estimation from the surface electromagnetic (EM) data. Studies are carried out aimed at estimating the feasibility of indirect temperature estimation in the geologically complicated areas of the Earth crust from the electromagnetic data collected at the surface. Basing on the neuronet analysis of magnetotelluric (MT) and temperature data measured at the Bishkek geodynamical testing ground in the northern Tien Shan, optimal methodologies for calibration and application of indirect electromagnetic geothermometer are developed. It is shown that the temperature estimation my means of the EM geothermometer calibrated by 6–8 temperature logs results in 12% average relative error (instead of 30% achieved using only temperature logs). The availability of prior geological information about the region under study and preliminary analysis of the local heterogeneities' indicators determined from the available MT data make it possible rejection of inappropriate site locations that may, in turn, decrease average error to only 11%.The results of the electromagnetic temperature extrapolation in depth indicate that the extrapolation accuracy essentially depends on the ratio between the well length and the extrapolation depth. In particular, in extrapolation to a depth twice as large as the well depth the relative error is 5–6%, and in case of its threefold excess the error is around 20%. This result makes it possible to increase significantly the deepness of indirect temperature estimation in the Earth interior (in particular, for geothermal exploration) based on the available temperature logs.     

The relationship between sea surface temperature anomalies and atmospheric circulation in GCM experiments

Several 19-year integrations of the Hamburg version of the ECMWF/T21 general circulation model driven by the monthly mean sea surface temperature (SST) observed in 1970–1988 were examined to study extratropical response of the atmospheric circulation to SST anomalies in the Northern Hemisphere in winter. In the first 19-years run SST anomalies were prescribed globally (GAGO run), and in two others SST monthly variability was limited to extratropical regions (MOGA run) and to tropics (TOGA run), respectively. A canonical correlation analysis (CCA), which select from two time-dependent fields optimally correlated pairs of patterns, was applied to monthly anomalies of SST in the North Alantic and Pacific Oceans and monthly anomalies of sea level pressure and 500 hPa geopotential height in the Northern Hemisphere. In the GAGO run the best correlated atmospheric pattern is global and is characterized by north-south dipole structures of the same polarity in the North Atlantic and the North Pacific sectors. In the MOGA and TOGA experiments the atmospehric response is more local than in the GAGO run with main centers in the North Atlantic and North Pacific, respectively. The extratropical response in the GAGO run is not equal to the sum of the responses in the MOGA and TOGA runs. The artificial meridional SST gradients at 25°–30°N probably influence the results of the MOGA and TOGA runs. The atmopsheric modes found by the CCA were compared with the normal modes of the barotropic vorticity equation linearized about the 500 hPa. winter climate. The normal modes with smallest eigenvalues are similar to the model leading variability modes and canonical patterns of 500 hPa geopotential height. The corresponding eigenvectors of the adjoint operator, which represent an external forcing optimal for exciting normal modes, have a longitudinal structure with maxima in regions characterized by enhanced high frequency baroclinic activity over both oceans.     

Peculiarities of the Formation of the Interference Structure of Scalar-Vector Acoustic Fields on the Shelf of the Sea of Japan

The results of experimental study of the spatial structure of the scalar-vector acoustic field formed during towing of a tone low-frequency emitter over the shelf of the Sea of Japan are discussed. The experiment was accomplished by towing the source of a tone signal with a frequency of 134 Hz at a depth of 20 m over various acoustic tracks at distances up to 10 km from an integrated receiving system consisting of a receiver of acoustic pressure and three orthogonal components of the acoustic pressure gradient. Special attention has been focused on study of the interference structure of the scalar and vector fields with provision of the technical reliability of the method and the results of the experiment under controlled hydrological conditions. We discuss the quantitative characteristics and peculiarities of the interference formation along tracks that differ in depth. The unique results of comparing the horizontal and vertical components of the fields are most interesting of all. They allowed us to reveal the existence of eddy structures in the acoustic field of the source over several tracks. We analyze the possibility of practical application of the results of our research.

     

The application of an indirect electromagnetic geothermometer to temperature extrapolation in depth

We study the feasibility of the application of an indirect EM geothermometer, developed recently, to the temperature extrapolation in depth using magnetotelluric data collected in the seismically active northern Tien Shan faulted area (Bishkek Geodynamic Test Site, Kyrgyzstan) and Hengill geothermal zone (Iceland). The approach used is based on the artificial neural network technique, which does not imply the prior knowledge of the electrical conductivity mechanisms on the one hand and provides temperature estimates based on the analysis of the implicit conductivity-temperature relations, on the other.
The samples for neuronet teaching consisted in the well temperature records and electrical conductivity values determined for the same depths from the magnetotelluric data measured in the vicinities of eight boreholes in each testing area. The testing of the taught neuronets was carried out using the temperature records not involved in the teaching process. The results indicate that the temperature extrapolation accuracy essentially depends on the ratio between the well length and the extrapolation depth. In particular, in extrapolation to a depth twice as large as the well depth the relative error is 5–6% and in case of threefold excess, the error is around 20%. This result makes it possible to increase significantly the depth of indirect temperature estimation in the Earth's interior (in particular, for geothermal exploration) based on the available temperature logs.
The practical application of an indirect electromagnetic geothermometer could provide the following facilities: 1) more exact temperature estimation in the extrapolation mode; 2) remote temperature estimates in the boreholes in areas characterized by extreme conditions for conventional geothermometers.     

A conceptual model of the copper–porphyry ore formation based on joint analysis of deep 3D geophysical models: Sorskoe complex (Russia) case study

Joint analysis of deep three-dimensional models of the electrical resistivity, seismic velocity, and density of the complex hosting the Sorskoe Cu–Mo deposit (Russia) is carried out aimed at finding geophysical markers characterizing the areas of ore generation, transportation and deposition. The three-dimensional lithology model of the study area is built based on the empirical relationship between the silica content of the rocks and seismic velocities. It is in agreement with geological and geochemical studies provided in this area earlier and could be used as a basis for forecasting locations of the copper–molybdenum ore deposits at depth. A conceptual model of the copper–porphyry complex explaining the mechanisms of ore generation, transportation from the lower to the upper crust and deposition in the upper crust is suggested. In particular, it is supposed that post-magmatic supercritical gas–water ore-bearing fluids are upwelling through the plastic crust due to the sliding of the fluid films along the cleavage planes of the foliated rocks while at the depths of the brittle upper crust this mechanism could be changed by volumetric fluid transportation along the network of large pores and cracks.     

Warming hiatus and evergreen conifers in Altay-Sayan Region,Siberia

"Warming hiatus" occurred in the AltaySayan Mountain Region, Siberia in c. 1997–2014. We analyzed evergreen conifer(EGC) stands area(satellite data) and trees(Siberian pine, Pinus sibirica Du Tour, Siberian fir, Abies sibirica Ledeb.) growth increment(dendrochronology data) response to climate variables before and during the hiatus. During the hiatus, EGC area increased in the highlands(1000 m)(+30%), whereas at low and middle elevations(1000 m. a.s.l.) the EGC area decreased(-7%). The EGC area increase was observed on the rain-ward northwest slopes mainly. In highlands, EGC area increase mainly correlated with summer air temperature, whereas at low and middle elevations EGC area decrease correlated with drought index SPEI and vapor pressure deficit(VPD). EGC mortality(fir and Siberian pine) in lowland was caused by the synergy of water stress(inciting factor) and barkbeetle attacks(contributing factor). Tree growth increment(GI) dynamics differs with respect to elevation. At high elevation(1700 m) GI permanently increased since warming onset, whereas at the middle(900 m) and low elevations(450 m) GI increased until c. 1983 yr. with followed depression. That GI "breakpoint" occurred about a decade before hiatus onset. In spite of growth depression, during hiatus GI was higher than that in pre-warming period. At high elevation, GI positively responded to elevated June temperatures and negatively to moisture increase(precipitation, root zone moisture content, VPD, and SPEI). At low elevation GI negatively responded to June temperatures and positively to moisture increase. For both, low and high elevation, these patterns persisted throughout the study period(1967–2014). On the contrary, at middle elevations GI dependence on climate variables switch after breakpoint year(1983). Before breakpoint, June air temperature(positive correlation) and moisture(negative correlations) controlled GI. Further temperature increase leads GI depression and switched correlation signs to opposite(from positive to negative with temperature, and from negative to positive with moisture variables).     

Seasonal and Annual Fluxes of Nutrients and Organic Matter from Large Rivers to the Arctic Ocean and Surrounding Seas

River inputs of nutrients and organic matter impact the biogeochemistry of arctic estuaries and the Arctic Ocean as a whole, yet there is considerable uncertainty about the magnitude of fluvial fluxes at the pan-Arctic scale. Samples from the six largest arctic rivers, with a combined watershed area of 11.3?×?10⁶?km², have revealed strong seasonal variations in constituent concentrations and fluxes within rivers as well as large differences among the rivers. Specifically, we investigate fluxes of dissolved organic carbon, dissolved organic nitrogen, total dissolved phosphorus, dissolved inorganic nitrogen, nitrate, and silica. This is the first time that seasonal and annual constituent fluxes have been determined using consistent sampling and analytical methods at the pan-Arctic scale and consequently provide the best available estimates for constituent flux from land to the Arctic Ocean and surrounding seas. Given the large inputs of river water to the relatively small Arctic Ocean and the dramatic impacts that climate change is having in the Arctic, it is particularly urgent that we establish the contemporary river fluxes so that we will be able to detect future changes and evaluate the impact of the changes on the biogeochemistry of the receiving coastal and ocean systems.     

Features of the Formation of the Pulse Characteristics of Waveguides by the Long-Range Propagation of Acoustic Signals in Underwater Sound Channels

Doklady Earth Sciences - The results of experimental studies on the features of propagation and reception of broadband pulsed signals in an underwater sound channel (USC) at a distance of 300 km...