Earthquake locations and seismic wave propagation in the upper 250 km of the Tonga island arc

1969 ◽  
Vol 59 (3) ◽  
pp. 1115-1135
Author(s):  
Walter Mitronovas ◽  
Bryan Isacks ◽  
Leonardo Seeber
Keyword(s):  
Seismic Waves ◽  
Seismic Wave Propagation ◽  
Island Arc ◽  
Seismic Zone ◽  
Magma Chambers ◽  
Uppermost Mantle ◽  
Short Term ◽  
High Attenuation ◽  
Upper Limit ◽  
Anomalous Propagation

abstract This paper reports results of a series of short-term seismic observations made on nearly all the major island groups of the Tonga island arc. These data extend the mapping of anomalous propagation of seismic waves from earthquakes beneath the island arc reported by Oliver and Isacks (1967), and significantly increase the number of accurately located earthquakes beneath the Tonga Islands. The data of this paper, combined with those of Sykes et al (1969), indicate that the inclined seismic zone of the Tonga island arc is very thin even at shallow depths. Most of the hypocenters are confined to a slab of about 25 km thickness. This thickness probably still reflects the precision of locations and may only be a measure of the upper limit of the thickness of the seismic zone. The inclined seismic zone, which has a dip of about 45° at intermediate depths in the mantle, appears to decrease in dip or bend over at depths less than about 50 km and appears to intersect the surface at or near the axis of the trench. The wedge-shaped region above the inclined seismic zone appears to be relatively aseismic, although some minor seismic activity has been located at shallow depths beneath the line of active volcanoes. P and S phases with anomalously large amplitudes and frequencies from deep earthquakes (> 400 km) were observed at all sites occupied in Tonga, including sites on two volcanoes. These observations and observations from shallower events include ray paths that emerge nearly vertically beneath the volcanoes. Thus, any region of high attenuation (low Q) below the volcanoes, such as magma chambers, must be limited in extent. These data, in conjunction with regional observations of Sn, indicate that a broad zone of low Q material in the uppermost mantle exists west of the volcanoes on the concave side of the arc. However, the P and S phases recorded on the volcanic ridge exhibit an emergent and drawn-out character that contrasts with the sharp and impulsive character of phases recorded on the non-volcanic ridge. These observations are interpreted to indicate considerable heterogeneity beneath the volcanoes.

Reconnaissance seismic refraction-reflection surveys in northwestern New Mexico

1984 ◽  
Vol 74 (4) ◽  
pp. 1263-1274
Author(s):  
Lawrence H. Jaksha ◽  
David H. Evans
Keyword(s):  
New Mexico ◽  
Wave Velocity ◽  
Lower Crust ◽  
Seismic Waves ◽  
Seismic Refraction ◽  
Velocity Model ◽  
P Wave ◽  
Uppermost Mantle ◽  
P Wave Velocity ◽  
Crustal Thinning

Abstract A velocity model of the crust in northwestern New Mexico has been constructed from an interpretation of direct, refracted, and reflected seismic waves. The model suggests a sedimentary section about 3 km thick with an average P-wave velocity of 3.6 km/sec. The crystalline upper crust is 28 km thick and has a P-wave velocity of 6.1 km/sec. The lower crust below the Conrad discontinuity has an average P-wave velocity of about 7.0 km/sec and a thickness near 17 km. Some evidence suggests that velocity in both the upper and lower crust increases with depth. The P-wave velocity in the uppermost mantle is 7.95 ± 0.15 km/sec. The total crustal thickness near Farmington, New Mexico, is about 48 km (datum = 1.6 km above sea level), and there is evidence for crustal thinning to the southeast.

scholarly journals Seismic wave propagation in anisotropic ice – Part 1: Elasticity tensor and derived quantities from ice-core properties

2015 ◽  
Vol 9 (1) ◽  
pp. 367-384 ◽  
Author(s):  
A. Diez ◽  
O. Eisen
Keyword(s):  
Seismic Waves ◽  
Dynamic Behaviour ◽  
Ice Core ◽  
Ice Cores ◽  
Seismic Wave Propagation ◽  
Elasticity Tensor ◽  
Reflection Coefficients ◽  
Seismic Velocities ◽  
Crystal Anisotropy ◽  
Elasticity Tensors

Abstract. A preferred orientation of the anisotropic ice crystals influences the viscosity of the ice bulk and the dynamic behaviour of glaciers and ice sheets. Knowledge about the distribution of crystal anisotropy is mainly provided by crystal orientation fabric (COF) data from ice cores. However, the developed anisotropic fabric influences not only the flow behaviour of ice but also the propagation of seismic waves. Two effects are important: (i) sudden changes in COF lead to englacial reflections, and (ii) the anisotropic fabric induces an angle dependency on the seismic velocities and, thus, recorded travel times. A framework is presented here to connect COF data from ice cores with the elasticity tensor to determine seismic velocities and reflection coefficients for cone and girdle fabrics. We connect the microscopic anisotropy of the crystals with the macroscopic anisotropy of the ice mass, observable with seismic methods. Elasticity tensors for different fabrics are calculated and used to investigate the influence of the anisotropic ice fabric on seismic velocities and reflection coefficients, englacially as well as for the ice–bed contact. Hence, it is possible to remotely determine the bulk ice anisotropy.

scholarly journals Vertical to Horizontal Spectral Ratio (VHSR) Response of Seismic Wave Propagation in a Homogeneous Elastic – Poroelastic Medium Using The Spectral Finite Element Method

2021 ◽  
Vol 11 (1) ◽  
pp. 95
Author(s):  
Sudarmaji Saroji ◽  
Budi Eka Nurcahya ◽  
Nivan Ramadhan Sugiantoro
Keyword(s):  
Finite Element Method ◽  
Elastic Medium ◽  
Seismic Waves ◽  
Low Frequency ◽  
Seismic Wave Propagation ◽  
P Wave ◽  
Poroelastic Medium ◽  
Compressional Waves ◽  
Spectral Finite Element Method ◽  
Spectral Finite Element

<p>Numerical modeling of 2D seismic wave propagation using spectral finite element method to estimate the response of seismic waves passing through the poroelastic medium from a hydrocarbon reservoir has been carried out. A hybrid simple model of the elastic - poroelastic - elastic with a mesoscopic scale element size of about 50cm was created. Seismic waves which was in the form of the ricker function are generated on the first elastic medium, propagated into the poroelastic medium and then transmitted to the second elastic medium. Pororoelastic medium is bearing hydrocarbon fluid in the form of gas, oil or water. Vertical and horizontal component of velocity seismograms are recorded on all mediums. Seismograms which are recorded in the poroelastic and second elastic medium show the existence of slow P compressional waves following fast P compressional waves that do not appear on the seismogram of the first elastic medium. The slow P wave is generated when the fast P wave enters the interface of the elastic - poroelastic boundary, propagated in the poroelastic medium and is transmited to the second elastic medium. The curves of Vertical to horizontal spectrum ratio (VHSR) which are observed from seismograms recorded in the poroelastic and the second elastic medium show that the peak of VHSR values at low frequency correlated with the fluid of poroelastic reservoir. The highest VHSR value at the low frequency which is recorded on the seismogram is above the 2.5 Hz frequency for reservoirs containing gas and oil in the second elastic medium, while for the medium containing water is the highest VHSR value is below the 2.5 Hz frequency.</p>

scholarly journals Transient electromagnetic radiation of the lithosphere in a seismically active region

2019 ◽  
Vol 127 ◽  
pp. 03006
Author(s):  
Yiyang Luo ◽  
Nguyen Xuan An ◽  
Vladislav Lutsenko ◽  
Vladimir Uvarov
Keyword(s):  
Electromagnetic Field ◽  
Active Region ◽  
Electromagnetic Radiation ◽  
Seismic Waves ◽  
Earth’S Crust ◽  
Schumann Resonance ◽  
Short Term ◽  
Transient Electromagnetic ◽  
Earth's Crust ◽  
High Level

To study the electromagnetic radiation of the lithosphere associated with seismic waves, we used the recordings of the natural electromagnetic radiation obtained under conditions of weak industrial noise and a high level of microseismicity in the ELF-VLF wave bands. It is shown that these data contain information about the surface waves of the Earth’s crust and are accompanied by a frequency close to the first harmonic of the Schumann resonance. The distribution of spikes over thresholds is obtained, which can be indicators of the activity in the processes of the Earth’s crust. The averaged form of the spikes for different components of the electromagnetic field is obtained. Attention is drawn to the differences in the various components of the electromagnetic field and their diurnal differences are analyzed. The possibility of using the approach to predict the short-term movement of the Earth’s crust is considered.

Geology, petrology and tectonomagmatic evolution of the plutonic crustal rocks of the Sabzevar ophiolite, NE Iran

2013 ◽  
Vol 150 (5) ◽  
pp. 862-884 ◽  
Author(s):  
MORTEZA KHALATBARI JAFARI ◽  
HASSAN A. BABAIE ◽  
MOJTABA MIRZAIE
Keyword(s):  
Subduction Zone ◽  
Subduction Zones ◽  
Island Arc ◽  
Magma Chambers ◽  
Northern Margin ◽  
Crustal Rocks ◽  
Microscopic Studies ◽  
Element Enrichment ◽  
Spider Diagrams ◽  
Ocean Ridge

AbstractThe plutonic crustal sequence exposed northeast of Sabzevar is part of the ophiolitic belt of Sabzevar that occurs along the northern margin of the Central Iran micro-continent. The sequence includes olivine and pyroxene gabbro with cumulate characteristics, isotropic gabbro, foliated gabbro and a diabase sheeted dyke complex cut by wehrlite and olivine websterite intrusions, and pegmatite gabbro and plagiogranite as small intrusions and dykes. The sequence is comparable to gabbros in known ophiolite complexes. Microscopic studies show an abundance of the mesocumulate and heteradcumulate textures that represent open system magma chambers, which are common in supra-subduction zones. The olivine → plagioclase → clinopyroxene → ± orthopyroxene → amphibole trend of mineralization in the gabbros, similar to mid-ocean ridge basalt (MORB), and olivine → clinopyroxene → ± orthopyroxene → plagioclase → amphibole, similar to arc rocks, indicate the diversity in the formation of these rocks, and represent petrographic evidence of their formation in a supra-subduction zone. The rocks have calc-alkaline to tholeiitic affinities, and niobium depletion in the spider diagrams of diabase that matches the patterns of island arc magma. These patterns, and the light rare earth element enrichment of the diabase and plagiogranite, suggest the effect and introduction of the fluids, originating from the subducting slab, beneath the mantle wedge. The low titanium compositions, matching those of arc diabase and plagiogranite, plot in the island arc to MORB tectonomagmatic fields, and suggest formation of the Sabzevar ophiolitic plutonic crustal sequence in a supra-subduction zone during Late Cretaceous time.

Ferro-andesites in the Grande Ronde Basalt: their composition and significance in studies of the origin of the Columbia River Basalt Group

1995 ◽  
Vol 32 (4) ◽  
pp. 424-436 ◽  
Author(s):  
R. StJ. Lambert ◽  
V. E. Chamberlain ◽  
J. G. Holland
Keyword(s):  
Chemical Composition ◽  
Columbia River ◽  
Special Consideration ◽  
Negative Slope ◽  
Magma Chambers ◽  
Uppermost Mantle ◽  
Average Value ◽  
Isotopic Compositions ◽  
Columbia River Basalt ◽  
Columbia River Basalt Group

Flows from the Grande Ronde Basalt of the Columbia River Basalt Group include several with the chemical composition of ferro-andesites. These flows have SiO2 > 55%, MgO < 4%, and also have higher Fe/Mg than the average value for Grande Ronde Basalt. They are also distinctly richer in Cs, Rb, K, Ba, La, Ce, Th, and U than the remainder of the Grande Ronde Basalt flows, and possess small negative Eu anomalies. Their Pb isotopic compositions define a mixing line with a negative slope on a 206Pb/204Pb versus 207Pb/204Pb plot. Their Nd isotopic compositions lie between 143Nd/144Nd = 0.51252 and 0.51264, and their Sr isotopic compositions lie between 87Sr/86Sr = 0.7055 and 0.7060. These values define the enriched end of the Columbia River Basalt Group spectrum on a Sr–Nd epsilon diagram (excluding the Saddle Mountains Basalt). These ferro-andesite flows also form a compositional end member of the Columbia River Basalt Group and are sufficiently distinctive to warrant special consideration. We compare them with lavas from other tholeiitic provinces. Petrogenetically, they can be related to the Grande Ronde Basalt low-Mg basalts by plagioclase fractionation, or by clinopyroxene fractionation in partially melted eclogites. However, the situation may not be that simple, as their unique isotopic compositions are closely related to those of parental mantle materials, perhaps thus requiring separate reservoirs and (or) sources. Extending this argument to other parts of the Columbia River Basalt Group suggests that the origin of these basalts may be in a system of comparatively small magma chambers in the uppermost mantle, frequently replenished from a variety of sources.

How loan interest rate liberalization affects firms’ loan maturity structure

2014 ◽  
Vol 4 (2) ◽  
pp. 153-167 ◽  
Author(s):  
Jianfang Zhou ◽  
Jingjing Wang ◽  
Jianping Ding
Keyword(s):  
Interest Rate ◽  
Interest Rates ◽  
Manufacturing Companies ◽  
Short Term ◽  
Data Set ◽  
Content Type ◽  
Interest Rate Liberalization ◽  
Upper Limit ◽  
Maturity Structure

Purpose – After loan interest rate upper limit deregulation in October 2004, the financing environment in China changed dramatically, and the banks were eligible for risk compensation. The purpose of this paper is to focus on the influence of the loan interest rate liberalization on firms’ loan maturity structure. Design/methodology/approach – Based on Rajan's (1992) model, the authors constructed a trade-off model of how the banks choose long-term and short-term loans scales, and further analyzed banks’ loan term decisions under the loan interest rate upper limit deregulation or collateral cases. Then the authors used an unbalanced panel data set of 586 Chinese listed manufacturing companies and 9,376 observations during the period 1996-2011 to testify the theoretical conclusion. Furthermore, the authors studied the effect on firms with different characteristics of ownership or scale. Findings – The results show that the loan interest rate liberalization significantly decreases the private companies’ reliance on short-term loans and increases sensitivity to interest rates of state-owned companies’ long-term loans. But the results also show that the companies’ ownership still plays a key role on the long-term loans availability. When monetary policy tightened, small companies still have to borrow short-term loans for long-term purposes. As the bank industry is still dominated by state-owned banks and the deposit interest rate has upper limits, the effect of the loan interest rate liberalization on easing long-term credit constraints is limited. Originality/value – From a new perspective, the content and findings of this paper contribute to the study of the effect of the interest rate liberalization on China economy.

Modelling the effects of diffusive-viscous waves in a 3-D fluid-saturated media using two numerical approaches

2020 ◽  
Vol 224 (2) ◽  
pp. 1443-1463
Author(s):  
Victor Mensah ◽  
Arturo Hidalgo
Keyword(s):  
Seismic Wave ◽  
Fourth Order ◽  
Seismic Waves ◽  
Time Discretization ◽  
Seismic Wave Propagation ◽  
Second Order ◽  
Finite Volume Scheme ◽  
Fluid Saturation ◽  
Runge Kutta ◽  
Saturated Medium

SUMMARY The accurate numerical modelling of 3-D seismic wave propagation is essential in understanding details to seismic wavefields which are, observed on regional and global scales on the Earth’s surface. The diffusive-viscous wave (DVW) equation was proposed to study the connection between fluid saturation and frequency dependence of reflections and to characterize the attenuation property of the seismic wave in a fluid-saturated medium. The attenuation of DVW is primarily described by the active attenuation parameters (AAP) in the equation. It is, therefore, imperative to acquire these parameters and to additionally specify the characteristics of the DVW. In this paper, quality factor, Q is used to obtain the AAP, and they are compared to those of the visco-acoustic wave. We further derive the 3-D numerical schemes based on a second order accurate finite-volume scheme with a second order Runge–Kutta approximation for the time discretization and a fourth order accurate finite-difference scheme with a fourth order Runge–Kutta approximation for the time discretization. We then simulate the propagation of seismic waves in a 3-D fluid-saturated medium based on the derived schemes. The numerical results indicate stronger attenuation when compared to the visco-acoustic case.

Double seismic zone beneath the Mariana Island Arc

1981 ◽  
Vol 86 (B8) ◽  
pp. 7013 ◽  
Author(s):  
Ilene R. Samowitz ◽  
Donald W. Forsyth
Keyword(s):  
Island Arc ◽  
Seismic Zone ◽  
Double Seismic Zone ◽  
Mariana Island Arc
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