Deep Focus Earthquake as a Result of a Hydraulic Shock in the Mantle of the Earth

2019 ◽  
Author(s):  
Serguei Bychkov
Keyword(s):  
Hydraulic Shock ◽  
The Earth ◽  
Deep Focus

scholarly journals Global earthquakes in the 2020 second half according to the GS RAS

2021 ◽  
Vol 3 (1) ◽  
pp. 7-26
Author(s):  
Yuri Vinogradov ◽  
Mariya Ryzhikova ◽  
Natalia Petrov ◽  
Svetlana Poygina ◽  
Marina Kolomiets
Keyword(s):  
Seismic Energy ◽  
Aegean Sea ◽  
Focal Mechanisms ◽  
Intraplate Earthquake ◽  
Strong Earthquakes ◽  
Tatar Strait ◽  
The Earth ◽  
Deformation Processes ◽  
The Russian Federation ◽  
Deep Focus

The data on the seismicity of the Earth in the second half of 2020 at the level of strong earthquakes with magnitudes mb≥6.0 are given according to the data of the Alert Service of the Geophysical Survey RAS. The review also includes information on 54 tangible earthquakes in Russia and five earthquakes in adjacent territories that were felt in the settlements of the Russian Federation. Two of 67 strong earthquakes of the Earth with mb≥6.0 for the period under consideration were registered in the territory of Russia. For 15 strong earthquakes, the Alert Service published Information Messages within one or two days after their occurrence, for 14 earthquakes the information on focal mechanisms is provided. The strongest earthquake of the Earth with MS=7.9 occurred on July, 22 in the region of the Alaska Peninsula. The maximum human casualties and material damage during the study period were the result of the catastrophic intraplate earthquake with MS=6.8, which occurred on October, 30 in the Aegean Sea, near the Samos Island. As a result of the earthquake, 117 people died, 1054 were injured. The strongest earthquake on the territory of Russia was the deep-focus one with mb=6.4, which took place on November, 30 in the Tatar Strait, separating Sakhalin Island from continental Eurasia. The crustal Bystrinsk earthquake on September, 21 with MS=5.2, which occurred in the area of Lake Baikal, was felt with a maximum intensity I=6–7 on the territory of Russia. Comparative analysis of the rate of seismic energy released in the Globe in 2010-2020 showed that its value in the second half of 2020, as well as for 2019-2020 on average, is one of the lowest for the eleven-year period and indicates a seismic calm, which should be replaced by a period of intensification of global seismic and deformation processes

A new analytical method for finding the upper mantle velocity structure from P and S wave travel times of deep earthquakes

1969 ◽  
Vol 59 (2) ◽  
pp. 755-769
Author(s):  
K. L. Kaila
Keyword(s):  
Velocity Structure ◽  
Focal Depth ◽  
Least Square ◽  
Travel Times ◽  
S Wave ◽  
The Earth ◽  
Straight Line ◽  
Wave Travel ◽  
Deep Focus ◽  
Mantle Velocity

abstract A new analytical method for the determination of velocity at the hypocenter of a deep earthquake has been developed making use of P- and S-wave travel times. Unlike Gutenberg's method which is graphical in nature, the present method makes use of the least square technique and as such it yields more quantitative estimates of the velocities at depth. The essential features of this method are the determination from the travel times of a deep-focus earthquake the lower and upper limits Δ1 and Δ2 respectively of the epicentral distance between which p = (dT/dΔ) in the neighborhood of inflection point can be considered stationary so that the travel-time curve there can be approximated to a straight line T = pΔ + a. From p = (1/v*) determined from the straight line least-square fit made on the travel-time observation points between Δ1 and Δ2 for various focal depths, upper-mantle velocity structure can be obtained by making use of the well known relation v = v*(r0 − h)/r0, h being the focal depth of the earthquake, r0 the radius of the Earth, v* the apparent velocity at the point of inflection and v the true velocity at that depth. This method not only gives an accurate estimate of p, at the same time it also yields quite accurate value of a which is a function of focal depth. Calibration curves can be drawn between a and the focal depth h for various regions of the Earth where deep focus earthquakes occur, and these calibration curves can then be used with advantage to determine the focal depths of deep earthquakes in those areas.

Understanding earthquake from the granular physics point of view — Causes of earthquake, earthquake precursors and predictions

2018 ◽  
Vol 32 (07) ◽  
pp. 1850081 ◽  
Author(s):  
Kunquan Lu ◽  
Meiying Hou ◽  
Zehui Jiang ◽  
Qiang Wang ◽  
Gang Sun ◽  
...  
Keyword(s):  
Large Scale ◽  
Continuum Theory ◽  
Earthquake Precursors ◽  
Point Of View ◽  
The Earth ◽  
Discrete Nature ◽  
Granular Physics ◽  
Deep Focus ◽  
Tectonic Forces ◽  
Precursory Information

We treat the earth crust and mantle as large scale discrete matters based on the principles of granular physics and existing experimental observations. Main outcomes are: A granular model of the structure and movement of the earth crust and mantle is established. The formation mechanism of the tectonic forces, which causes the earthquake, and a model of propagation for precursory information are proposed. Properties of the seismic precursory information and its relevance with the earthquake occurrence are illustrated, and principle of ways to detect the effective seismic precursor is elaborated. The mechanism of deep-focus earthquake is also explained by the jamming–unjamming transition of the granular flow. Some earthquake phenomena which were previously difficult to understand are explained, and the predictability of the earthquake is discussed. Due to the discrete nature of the earth crust and mantle, the continuum theory no longer applies during the quasi-static seismological process. In this paper, based on the principles of granular physics, we study the causes of earthquakes, earthquake precursors and predictions, and a new understanding, different from the traditional seismological viewpoint, is obtained.

The Distribution of Deep-focus Earthquakes

1937 ◽  
Vol 74 (7) ◽  
pp. 316-324 ◽  
Author(s):  
Charles Davison
Keyword(s):  
Northern Hemisphere ◽  
Depth Of Focus ◽  
The Earth ◽  
Deep Focus

During the years 1918–1931, there were 270 earthquakes with unusually deep foci, 167 in the Northern Hemisphere, 101 in the Southern, and two with epicentres on the equator. The normal depth of focus is assumed to be about 50 km. or ·008 of the earth's radius. The focal depths of the above earthquakes range from ·005 to ·090 of the earth's radius below the normal depth, or from 50 to 380 miles beneath the surface. Throughout this paper, the depth, when given in terms of the earth's radius, is referred to the normal depth; when given in miles, to the surface of the earth.

The times of origin and depths of focus of intermediate and deep focus earthquakes: Model calculations

1981 ◽  
Vol 71 (5) ◽  
pp. 1539-1552
Author(s):  
A. L. Hales ◽  
K. J. Muirhead ◽  
L. Maki-Lopez
Keyword(s):  
Average Velocity ◽  
Epicentral Distance ◽  
Depth Range ◽  
Depth Of Focus ◽  
P Waves ◽  
Model Calculations ◽  
The Earth ◽  
Deep Focus ◽  
The Times ◽  
Time Of Origin

abstract Two methods for determining the time of origin, depth of focus, and the average velocities from the focus to the surface are described. The first stage in the first method is to determine the time of origin using a modification of the Wadati method. As was pointed out in 1973 by Kisslinger and Engdahl, the relation between (ts − tp and tp is nonlinear and it is necessary to allow for this nonlinearity by including a term in tp2 in the analysis. Thereafter the depth of focus and the average velocity can be found by a modification of the procedure used to determine the depth to a reflector in seismic reflection prospecting. It is necessary to allow for the sphericity of the Earth in this analysis. In the second method, the depth of focus is determined first by analyzing (ts − tp)2 as a function of x2, x being the epicentral distance. The average velocity of separation of S and P waves is also determined at this stage. Thereafter the time of origin and the average P and S velocities are determined. The results of the analysis of the calculated travel times for three models show that systematic errors in the depth of focus using these procedures are less than 2 km over the depth range of 60 to 640 km. Preliminary results of the analysis of a limited set of Japanese earthquakes by these methods give estimates of depth smaller than those given by ISC for depths less than 300 km. For deeper earthquakes, these methods give foci deeper than the ISC, but in these cases the observations close to the epicenter are inadequate for reliable analysis.

scholarly journals Attenuation of shear waves in the upper and lower mantle

1964 ◽  
Vol 54 (6A) ◽  
pp. 1855-1864 ◽  
Author(s):  
Robert L. Kovach ◽  
Don L. Anderson
Keyword(s):  
Lower Mantle ◽  
Seismic Waves ◽  
Wave Amplitude ◽  
Body Wave ◽  
Shear Waves ◽  
Normal Incidence ◽  
Frequency Range ◽  
Spectral Ratios ◽  
The Earth ◽  
Deep Focus

abstract The attenuation of seismic waves is a direct measure of the absorption due to nonelastic processes in the earth. The well known difficulties in obtaining body wave amplitude decrement data have been avoided by studying the spectral ratios of multiple ScS and sScS phases from two deep focus earthquakes recorded at near normal incidence. The average Q, for shear, in the mantle is about 600 for the frequency range 0.015 to 0.07 cps. Assuming that equal radiation occurs upwards and downwards from the source the average Q for the upper 600 km of the mantle is determined to be about 200 and about 2200 for the rest of the mantle. The value for Q at the base of the mantle is at least 5000 for shear waves.

Direct and Indirect Evidence

1999 ◽  
Author(s):  
Naomi Oreskes
Keyword(s):  
National Research Council ◽  
Continental Drift ◽  
Indirect Evidence ◽  
California Institute Of Technology ◽  
The Earth ◽  
Elastic Rebound ◽  
Order Of Magnitude ◽  
Internal Constitution ◽  
Institute Of Technology ◽  
Deep Focus

At the California Institute of Technology in the mid-1940s, a young Henry William Menard—later an expert on submarine physiography and director of the U.S. Geological Survey—learned about continental drift from Beno Gutenberg. For although most American earth scientists considered the question of drift settled, many Europeans did not. Among them was “Dr. G,” famous for his pioneering work on microseisms (the continual seismic disturbances that form the background “noise” of seismographs) and deep-focus earthquakes, who had come to Caltech from Germany in 1930. In 1939, he edited Internal Constitution of the Earth, part of a series entitled Physics of the Earth sponsored by the National Research Council. Gutenberg’s chapter, “Hypotheses on the Development of the Earth’s Crust and their Implications,” focused on the evidence for a plastic crustal substrate and “currents” within it. More than just an idea, he argued, subcrustal currents were necessary—in the past and at present — to account for both isostasy and horizontal crustal dislocations: “Many writers have expressed the belief that the strength of the interior of the earth prevents any currents today. The results of geophysical research, however, leave no doubt that such currents still exist. . . . [either] as a consequence of changes produced by disturbances at the surface [or as ] the primary cause of movement at the surface.” Gutenberg’s course at Caltech reflected these views. The strength of the crust was “enough to support [the] highest mountains,” he explained in class, but isostasy demonstrated that this strength “decreases downwards, and below 40 km or so plastic flow may occur.” This flow was implicated in both geological and seismological processes. Among the forces causing earthquakes, for example, Gutenberg suggested “elastic rebound as a release of shear due to sub-crustal flow and contraction of the crust & possibly differential movements in the crust from continental drift.” He noted that the energy release associated with earthquakes was “of the same order of magnitude as that due to temperature gradient,” which suggested that the most likely cause of plas tic flow was internal temperature differentials. One preexamination review sheet asked students for the meaning of isostasy and of “Wegener’s hypothesis.”

Characteristic periods of fundamental and overtone oscillations of the earth following a deep-focus earthquake

1972 ◽  
Vol 62 (1) ◽  
pp. 247-274 ◽  
Author(s):  
A. A. Nowroozi
Keyword(s):  
Phase Velocity ◽  
Upper Mantle ◽  
Ocean Bottom ◽  
The Earth ◽  
The Pacific ◽  
Spectral Peaks ◽  
Deep Focus ◽  
Ray Parameter ◽  
The Relationship ◽  
Spheroidal Oscillations

Abstract The deep-focus earthquake of July 31, 1970, (1.5°S, 72.6°W, h = 651 km, Mb = 7.1) excited a set of fundamental and overtone free oscillations. From analysis of seismograms recorded at Berkeley, California, at an ocean-bottom station in the Pacific, and at Ogdensburg, New Jersey, the fundamental spheroidal oscillations, l = 10-98, and a number of overtones with n = 1, 2, and 3, fundamental torsional oscillations, l = 3-70, and overtones with n = 1, 2, 3, and 4, are identified. The majority of resolved spectral peaks are above the 95 per cent confidence level. For some modes with periods less than 300 sec, the observed period at each station differs by up to 2 sec. This path-dependency of the period may thus suggest the existence of lateral heterogeneity in the upper mantle. The observed periods are compared to calculated periods for Haddon-Bullen's model HB1 and Derr's model DI-11; for fundamental modes the agreements are good, while differences up to 2 sec exist for some overtone modes. A relationship between order of oscillations, l, the frequency, nωl, and the ray parameter dt/dθ is derived, which is equivalent to the Jean's equation for phase velocity. The relationship implies that each mode with period nTl will travel with phase velocity dΔ/dt along its own ray with parameter dt/dθ. Other models will travel along the same ray if they have the same ray parameter.

Periodicity of deep-focus earthquakes*

1941 ◽  
Vol 31 (1) ◽  
pp. 33-82
Author(s):  
Howard McMurry
Keyword(s):  
Pressure Fluctuations ◽  
Focal Depth ◽  
Barometric Pressure ◽  
Great Depth ◽  
Earth Tides ◽  
The Earth ◽  
Stress Changes ◽  
Deep Focus ◽  
Stress Variations ◽  
Periodogram Analysis

Summary and Conclusions Data were assembled of about 320 earthquakes, including nearly all those available for which the determinations of epicentral location, time of occurrence, and focal depth were considered reliable. They were analyzed collectively and in selected geographical groups by the method of periodogram analysis which appeared most suitable. Tests were made on periods of 6, 12, and 14 months and for correlation with twice the lunar and solar hour angles. None of the results could be interpreted as other than accidental. However, the Japanese group gave a slight indication of a correlation with twice the solar hour angle, and the South American earthquakes with twice the lunar hour angle. Many additional data must first be accumulated and tested before any special significance can be attached to these results. The manner whereby small fluctuations in stress might be expected to determine the exact time of occurrence of an earthquake was reviewed. A study was then made of three possible sources of such trigger stresses which could be effective at great depth, namely, tidal stresses in the solid earth, stresses due to changes in sea level, and stresses due to variations in barometric pressure. Tidal stresses alone were considered in detail. It was concluded that tidal stress variations approximate harmonic changes sufficiently well to warrant a search for lunar hour angle correlations by the methods of periodogram analysis, but they are nevertheless too irregular to make the statistical results of such studies valuable in supplying information concerning the mechanics and environment of deep-seated earthquakes. Periodicity investigations of this type, even if successful, can be expected to do little more than indicate the causes which can influence earthquake occurrence times. The importance of other agencies in causing stress variations within the earth was studied. It was concluded that oceanic tidal loads, and to a much less degree erratic barometric fluctuations, are capable of producing stress changes comparable with those due to tides in the earth. The stresses from the earth tides in general dominate the others, although the effect of ocean tidal loading may be of primary importance under special circumstances. The irregularity of both ocean loads and barometric pressure fluctuations renders them unsuitable subjects for study. For the reasons given, the only stress changes that appear to warrant study with reference to their effect on earthquakes are those due to earth tides. The best chance of finding a definite correlation world be from a study of data of a large number of earthquakes which had occurred within relatively small regions, as only then is it justifiable to assume that all the earthquakes had been similarly affected by the triggering stress. Data at present available are far from sufficient to provide a satisfactory basis for such a study.

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