The first preliminary waves of the Nevada earthquake of December 20, 1932*

1935 ◽  
Vol 25 (1) ◽  
pp. 62-80 ◽  
Author(s):  
Perry Byerly
Keyword(s):  
Sudden Change ◽  
Simple Explanation ◽  
Depth Of Focus ◽  
Time Curve ◽  
P Waves ◽  
Long Period ◽  
First Motion ◽  
Straight Lines ◽  
Suggested Explanation ◽  
Period Motion

Summary The P travel-time curve of the Nevada earthquake is presented. It is drawn as a series of straight lines. It is near Δ = 28° that the data outline most clearly the sudden change in slope of the curve, but definite evidence of overlapping of the branches is lacking. At Δ = 67° (approximately) the curve branches into two parts as did the curve of the Texas earthquake. Between 4° and 12° three parallel P curves are drawn. The suggested explanation of them is that they are due to transformations of an original P or S at boundaries near the focus. This would indicate a depth of focus of about fifteen kilometers. The nature of the first motion at the various stations shows a complex distribution which does not lead to a simple explanation of the forces acting at the focus. A long-period component of P waves is observed, and it is concluded that it is present from very near the beginning of the record, although often masked by shorter-period motion. It begins in opposite phase to the shorter-period motion accompanying it.

The Texas earthquake of August 16, 1931*

1934 ◽  
Vol 24 (2) ◽  
pp. 81-99
Author(s):  
Perry Byerly
Keyword(s):  
Travel Time ◽  
Travel Times ◽  
Time Curve ◽  
P Waves ◽  
First Order ◽  
First Motion ◽  
Order Discontinuity

Summary The travel-time curve of P for the Texas earthquake of August 16, 1931, shows that there is a definite break in the travel-time curve near Δ = 16°. This is interpreted as indicating a first-order discontinuity at a depth of about 300 kilometers. Another break in the travel-time curve at Δ = 25° is strongly suggested. Beyond Δ = 75° the curve has two branches, the lower following most existing curves, the upper following the Montana curve which latter seems to be a usual one for American earthquakes. This part of the curve is interpreted as indicating that the discontinuity at depth about 2,400 kilometers is a first-order one at which the speed of P waves drops discontinuously. From the direction of first motion on the records it is concluded that a sufficient source would have been motion on a fault of strike about N 35° W, the movement being up on the easterly side and down on the westerly side. The travel times of all waves read on the records are plotted on graphs. The scattering of all waves after P is marked.

scholarly journals A discontinuity in the dehydration of certain salt hydrates

1924 ◽  
Vol 106 (736) ◽  
pp. 215-222 ◽  
Keyword(s):  
High Temperature ◽  
Sudden Change ◽  
Barium Chloride ◽  
Heterogeneous Reactions ◽  
Interesting Problem ◽  
Random Series ◽  
Time Curve ◽  
Salt Hydrates ◽  
Straight Lines ◽  
Kinetics Of

Several investigators have studied the rate of loss of water from salt hydrates exposed in dry atmospheres at ordinary temperatures. The process for salts forming more than one hydrate consists of a series of stages, during each of which the evaporation proceeds at an approximately uniform rate. The existence of sudden changes in the rate of dehydration has been used as evidence of the existence of definite hydrates, even in cases where the hydrate concerned has not been isolated. Thus Richards (1) found a sudden change in rate with BaCl 2 . 2H 2 O at a point corresponding to the composition BaCl 2 . 1H 2 O. Davis and Eyre (2), in a recent paper on the “rehydration” of fibres and certain salts, state that the weight-time curve consists of a random series of parabolic segments and straight lines. The Odén-Keen Automatic Recording Balance (3) has rendered it possible to follow the progress of the dehydration and hydration of salt hydrates under conditions that were not possible by the methods of intermittent weighing hitherto adopted. The rehydration of anhydrous copper sulphatelu moist or saturated atmospheres showed no discontinuities similar to those found by Davis and Eyre. During the rapid dehydration of copper sulphate and barium chloride crystals, however, a characteristic break has been found. When these materials were dried at a high temperature it was found that the evaporation was either completely arrested or extremely slow for some minutes, when the composition of the residue could be represented by a definite hydrate such as CuSO 4 . 3H 2 O, CuSO 4 . 1H 2 O, or BaCl 2 . 1H 2 O. This phenomenon does not appear to have been observed previously, and its interpretation should provide an interesting problem in the kinetics of heterogeneous reactions.

The Hebgen Lake, Montana, earthquake of August 18, 1959: P waves

1962 ◽  
Vol 52 (2) ◽  
pp. 235-271
Author(s):  
Alan Ryall
Keyword(s):  
Travel Time ◽  
Sierra Nevada ◽  
Fault Plane ◽  
Time Curve ◽  
P Waves ◽  
Arrival Times ◽  
The Pacific ◽  
First Motion ◽  
Plane Solution ◽  
The Pacific Ocean

ABSTRACT The instrumental epicenter of the Hebgen Lake earthquake is found to lie within the region of surface faulting. The depth of focus had a maximum value of 25 kilometers. Times of P are studied in detail for epicentral distances less than 13 degrees. The apparent scatter of arrival times from 700 to 1400 kilometers can be explained by variations of the velocity of Pn between the physiographic provinces of the western United States. A comparison of observations for the Hebgen Lake earthquake with published times for blasts in Nevada and Utah indicates that the velocity of Pn in the central and eastern Basin and Range is about 7.5 km/sec, and that the crust in that region thickens toward the east and thins toward the south. A comparison of apparent velocities in northern California, in directions parallel and transverse to the structure, indicates that the crust thins by about 19 kilometers, from the edge of the Sierra Nevada to the Pacific Ocean. A discontinuity is observed in the travel-time curve at a distance of 24–25 degrees. Arrivals of P waves in the range 65–128 degrees fall on two parallel travel-time branches; this multiplicity in the travel-time curve may be related to repeated motion at the source. Travel-times of PKIKP appear to deviate from published curves. The fault-plane solution for the Hebgen Lake earthquake, together with a consideration of the first motion at Bozeman, Montana, indicates a focal mechanism of the dipole, or fault, type. The strike and dip of the instrumental fault plane agree well with observed ruptures at the surface.

Seismic wave energy inferred from long-period body wave inversion

1988 ◽  
Vol 78 (5) ◽  
pp. 1707-1724
Author(s):  
Masayuki Kikuchi ◽  
Yoshio Fukao
Keyword(s):  
Seismic Wave ◽  
Wave Energy ◽  
Body Wave ◽  
Empirical Relation ◽  
P Waves ◽  
Average Value ◽  
Long Period ◽  
Wave Inversion ◽  
Moment Ratio ◽  
Order Of Magnitude

Abstract The seismic wave energy is evaluated for 35 large earthquakes by inverting far-field long-period P waves into the multiple-shock sequence. The results show that the seismic wave energy thus obtained is systematically less than that inferred from the Gutenberg-Richter's formula with the seismic magnitude. The difference amounts to one order of magnitude. The results also show that the energy-moment ratio is well confined to a narrow range: 10−6 < ES/Mo < 10−5 with the average of ∼5 × 10−6. This average value is exactly one order of magnitude as small as the energy-moment ratio inferred from the Gutenberg-Richter's formula using the moment magnitude. Comparing the energy-moment ratio with Δσo/2μ, where Δσo and μ are the stress drop and the rigidity, we obtain an empirical relation: ES/Mo ∼ 0.1 × Δσ0/2μ. Such a relation can be interpreted in terms of a subsonic rupture where the energy loss due to cohesion is not negligible to the seismic wave energy.

Evidence of tectonic release from underground nuclear explosions in long-period P waves

1983 ◽  
Vol 73 (2) ◽  
pp. 593-613
Author(s):  
Terry C. Wallace ◽  
Donald V. Helmberger ◽  
Gladys R. Engen
Keyword(s):  
Upper Mantle ◽  
High Stress ◽  
Test Site ◽  
Strike Slip ◽  
Body Waves ◽  
Release Time ◽  
P Waves ◽  
Underground Nuclear Explosions ◽  
Nuclear Explosions ◽  
Long Period

abstract In this paper, we study the long-period body waves at regional and upper mantle distances from large underground nuclear explosions at Pahute Mesa, Nevada Test Site. A comparison of the seismic records from neighboring explosions shows that the more recent events have much simpler waveforms than those of the earlier events. In fact, many of the early events produced waveforms which are very similar to those produced by shallow, moderate-size, strike-slip earthquakes; the phase sP is particularly obvious. The waveforms of these explosions can be modeled by assuming that the explosion is accompanied by tectonic release represented by a double couple. A clear example of this phenomenon is provided by a comparison of GREELEY (1966) and KASSERI (1975). These events are of similar yields and were detonated within 2 km of each other. The GREELEY records can be matched by simply adding synthetic waveforms appropriate for a shallow strike-slip earthquake to the KASSERI observations. The tectonic release for GREELEY has a moment of 5 ՠ1024 dyne-cm and is striking approximately 340°. The identification of the sP phase at upper mantle distances indicates that the source depth is 4 km or less. The tectonic release time function has a short duration (less than 1 sec). A comparison of these results with well-studied strike-slip earthquakes on the west coast and eastern Nevada indicate that, if tectonic release is triggered fault motion, then the tectonic release is relatively high stress drop, on the order of several hundred bars. It is possible to reduce these stress drops by a factor of 2 if the tectonic release is a driven fault; i.e., rupturing with the P velocity. The region in which the stress is released for a megaton event has a radius of about 4 km. Pahute Mesa events which are detonated within this radius of a previous explosion have a substantially reduced tectonic release.

Near earthquakes in Central California*

1939 ◽  
Vol 29 (3) ◽  
pp. 427-462 ◽  
Author(s):  
Perry Byerly
Keyword(s):  
Least Squares ◽  
Travel Time ◽  
Sierra Nevada ◽  
Accurate Determination ◽  
Depth Of Focus ◽  
Surface Layers ◽  
P Waves ◽  
Central California ◽  
The Waves

Summary Least-squares adjustments of observations of waves of the P groups at central and southern California stations are used to obtain the speeds of various waves. Only observations made to tenths of a second are used. It is assumed that the waves have a common velocity for all earthquakes. But the time intercepts of the travel-time curves are allowed to be different for different shocks. The speed of P̄ is found to be 5.61 km/sec.±0.05. The speed for S̄ (founded on fewer data) is 3.26 km/sec. ± 0.09. There are slight differences in the epicenters located by the use of P̄ and S̄ which may or may not be significant. It is suggested that P̄ and S̄ may be released from different foci. The speed of Pn, the wave in the top of the mantle, is 8.02 km/sec. ± 0.05. Intermediate P waves of speeds 6.72 km/sec. ± 0.02 and 7.24 km/sec. ± 0.04 are observed. Only the former has a time intercept which allows a consistent computation of structure when considered a layer wave. For the Berkeley earthquake of March 8, 1937, the accurate determination of depth of focus was possible. This enabled a determination of layering of the earth's crust. The result was about 9 km. of granite over 23 km. of a medium of speed 6.72 km/sec. Underneath these two layers is the mantle of speed 8.02 km/sec. The data from other shocks centering south of Berkeley would not fit this structure, but an assumption of the thickening of the granite southerly brought all into agreement. The earthquakes discussed show a lag of Pn as it passes under the Sierra Nevada. This has been observed before. A reconsideration of the Pn data of the Nevada earthquake of December 20, 1932, together with the data mentioned above, leads to the conclusion that the root of the mountain mass projects into the mantle beneath the surface layers by an amount between 6 and 41 km.

scholarly journals The February 9, 1971 San Fernando earthquake: A study of source finiteness in teleseismic body waves

1978 ◽  
Vol 68 (1) ◽  
pp. 1-29 ◽  
Author(s):  
Charles A. Langston
Keyword(s):  
Near Field ◽  
Dislocation Line ◽  
Strong Motion ◽  
Body Waves ◽  
P Waves ◽  
Long Period ◽  
Short Period ◽  
Wave Forms ◽  
San Fernando ◽  
The Time Domain

abstract Teleseismic P, SV, and SH waves recorded by the WWSS and Canadian networks from the 1971 San Fernando, California earthquake (ML = 6.6) are modeled in the time domain to determine detailed features of the source as a prelude to studying the near and local field strong-motion observations. Synthetic seismograms are computed from the model of a propagating finite dislocation line source embedded in layered elastic media. The effects of source geometry and directivity are shown to be important features of the long-period observations. The most dramatic feature of the model is the requirement that the fault, which initially ruptured at a depth of 13 km as determined from pP-P times, continuously propagated toward the free surface, first on a plane dipping 53°NE, then broke over to a 29°NE dipping fault segment. This effect is clearly shown in the azimuthal variation of both long period P- and SH-wave forms. Although attenuation and interference with radiation from the remainder of the fault are possible complications, comparison of long- and short-period P and short-period pP and P waves suggest that rupture was initially bilateral, or, possibly, strongly unilateral downward, propagating to about 15 km depth. The average rupture velocity of 1.8 km/sec is well constrained from the shape of the long-period wave forms. Total seismic moment is 0.86 × 1026 dyne-cm. Implications for near-field modeling are drawn from these results.

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