The seismic waves from the Port Chicago explosion*

1946 ◽  
Vol 36 (4) ◽  
pp. 331-348
Author(s):  
Perry Byerly
Keyword(s):  
Sierra Nevada ◽  
Seismic Waves ◽  
Longitudinal Waves ◽  
Normal Waves ◽  
The Earth ◽  
Short Period ◽  
Differential Speed

Summary The records of the Port Chicago explosion alone suggest the conclusion that an averaged layering for California is 3 km. of rock of speed 5.0 km/sec. for longitudinal waves overlying a layer 11 km. thick of speed 5.6 km/sec., which in turn overlies a medium of speed 7.7 km/sec. No waves which traversed the mantle were observed. The root of the southern Sierra Nevada blocks the 7.7 km/sec. were even as it blocks the 8.0 km/sec. P normal waves. The air wave seems definitely recorded at Berkeley and Santa Clara as wave of period 3 or 4 seconds. The differential speed between the stations was normal, 342 m/sec. There is a suggestion of a short-period (0.5 sec.) air wave at Stanford with over-all speed of 333 m/sec. From study of the seismograms it is concluded that the energy in the earth waves was about 1016 ergs, or roughly of the order of one-thousandth of the probable energy released in the explosion.

scholarly journals Observations on seismic waves reflected at the core boundary of the earth*

1950 ◽  
Vol 40 (2) ◽  
pp. 95-109
Author(s):  
Samuel T. Martner
Keyword(s):  
Observational Data ◽  
Seismic Waves ◽  
Outer Boundary ◽  
Body Waves ◽  
Longitudinal Waves ◽  
The Core ◽  
The Earth ◽  
Core Boundary ◽  
Direct Body

Abstract Waves reflected from the outer boundary of the core of the earth often record trace amplitudes that appear excessive. A comparison of the observed displacements of these phases and the direct body waves is presented. Observational data seem to confirm the idea that the displacement ratios of the longitudinal waves reflected at the core to the longitudinal direct waves is larger than the presently recognized theory indicates. A discussion is included of some possible causes for this difference, but reasonable changes in accepted assumptions fail to explain the entire discrepancy.

The Origin of the Moon and its Relationship to the Origin of the Solar System

1962 ◽  
Vol 14 ◽  
pp. 133-148 ◽  
Author(s):  
Harold C. Urey
Keyword(s):  
Solar System ◽  
The Moon ◽  
The Past ◽  
The Earth ◽  
Short Period ◽  
Origin Of The Moon

During the last 10 years, the writer has presented evidence indicating that the Moon was captured by the Earth and that the large collisions with its surface occurred within a surprisingly short period of time. These observations have been a continuous preoccupation during the past years and some explanation that seemed physically possible and reasonably probable has been sought.

scholarly journals New Tools for the Optimized Follow-Up of Imminent Impactors

Universe ◽  
2021 ◽  
Vol 7 (1) ◽  
pp. 10
Author(s):  
Maddalena Mochi ◽  
Giacomo Tommei
Keyword(s):  
Orbit Determination ◽  
Main Belt ◽  
Impact Monitoring ◽  
The Earth ◽  
Current Observation ◽  
Short Period ◽  
Fly Eye ◽  
Near Earth Asteroids ◽  
Near Earth Objects

The solar system is populated with, other than planets, a wide variety of minor bodies, the majority of which are represented by asteroids. Most of their orbits are comprised of those between Mars and Jupiter, thus forming a population named Main Belt. However, some asteroids can run on trajectories that come close to, or even intersect, the orbit of the Earth. These objects are known as Near Earth Asteroids (NEAs) or Near Earth Objects (NEOs) and may entail a risk of collision with our planet. Predicting the occurrence of such collisions as early as possible is the task of Impact Monitoring (IM). Dedicated algorithms are in charge of orbit determination and risk assessment for any detected NEO, but their efficiency is limited in cases in which the object has been observed for a short period of time, as is the case with newly discovered asteroids and, more worryingly, imminent impactors: objects due to hit the Earth, detected only a few days or hours in advance of impacts. This timespan might be too short to take any effective safety countermeasure. For this reason, a necessary improvement of current observation capabilities is underway through the construction of dedicated telescopes, e.g., the NEO Survey Telescope (NEOSTEL), also known as “Fly-Eye”. Thanks to these developments, the number of discovered NEOs and, consequently, imminent impactors detected per year, is expected to increase, thus requiring an improvement of the methods and algorithms used to handle such cases. In this paper we present two new tools, based on the Admissible Region (AR) concept, dedicated to the observers, aiming to facilitate the planning of follow-up observations of NEOs by rapidly assessing the possibility of them being imminent impactors and the remaining visibility time from any given station.

Attenuation of short period seismic waves at Etna as compared to other volcanic areas

1987 ◽  
Vol 125 (6) ◽  
pp. 1039-1050 ◽  
Author(s):  
E. Del Pezzo ◽  
S. Gresta ◽  
G. Patané ◽  
D. Patané ◽  
G. Scarcella
Keyword(s):  
Seismic Waves ◽  
Short Period

scholarly journals Amplitudes of P, PP, and S and magnitude of shallow earthquakes*

1945 ◽  
Vol 35 (2) ◽  
pp. 57-69
Author(s):  
B. Gutenberg
Keyword(s):  
Absorption Coefficient ◽  
Shallow Earthquake ◽  
Transverse Waves ◽  
Longitudinal Waves ◽  
Longitudinal And Transverse Waves ◽  
The Core ◽  
The Earth ◽  
Shallow Earthquakes

Summary It is found that the absorption coefficient for longitudinal and transverse waves in the mantle of the earth as well as for longitudinal waves through the core is 0.00012 per km. In the average shallow earthquake about equal amounts of energy go into longitudinal and transverse waves. Equation (18), together with tables 2 and 4, permits the calculation of the magnitude of a shallow earthquake from the amplitudes of P, PP, or S.

JOINT 3D TRAVELTIME INVERSION OF P, S AND CONVERTED WAVES

2001 ◽  
Vol 09 (04) ◽  
pp. 1407-1416 ◽  
Author(s):  
GIULIANA ROSSI ◽  
ALDO VESNAVER
Keyword(s):  
Linear System ◽  
Seismic Waves ◽  
Velocity Fields ◽  
Traveltime Inversion ◽  
S Waves ◽  
The Earth ◽  
Converted Waves

Converted waves can play a basic role in the traveltime inversion of seismic waves. The sought velocity fields of P and S waves are almost decoupled, when considering pure P and S arrivals: their only connection are the possible common reflecting interfaces in the Earth. Converted waves provide new equations in the linear system to be inverted, which directly relates the two velocity fields. Since the new equations do not introduce additional unknowns, they increase the system rank or its redundancy, so making its solutions better constrained and robust.

scholarly journals Radar Observations of Comet Nuclei and Comae

2005 ◽  
Vol 13 ◽  
pp. 763-763
Author(s):  
Donald B. Campbell ◽  
John K. Harmon ◽  
Micael C. Nolan ◽  
Steven J. Ostro
Keyword(s):  
Cross Sections ◽  
Cometary Nucleus ◽  
Size Distributions ◽  
Radar Systems ◽  
The Earth ◽  
Radar Cross Sections ◽  
Short Period ◽  
Grain Size Distributions ◽  
Resolution Imaging

Nine comets have been detected with either the Arecibo (12.6 cm wavelength) or Goldstone (3.5 cm) radar systems. Included are six nucleus detections and five detections of echoes from coma grains. The radar backscatter cross sections measured for the nuclei correlate well with independent estimates of their sizes and are indicative of surface densities in the range of 0.5 to 1.0 g cm-3. Like most asteroids, comets appear to have surfaces that are very rough at scales much larger than the radar wavelength. Coma echo models can explain the radar cross sections using grain size distributions that include a substantial population of cm-sized grains. A long term goal of the cometary radar program has been the high resolution imaging of a cometary nucleus. Eleven short period comets are potentially detectable over the next two decades a few of which may be suitable for imaging. We are always waiting for the arrival of a new comet with an orbit that brings it within 0.1 AU of the earth.

Seismic Rays

2017 ◽  
Author(s):  
John A. Adam
Keyword(s):  
Inverse Problem ◽  
Seismic Tomography ◽  
Seismic Waves ◽  
Seismic Station ◽  
Three Dimensional ◽  
Arrival Times ◽  
The Earth ◽  
Straight Lines ◽  
Ray Path ◽  
Uniform Composition

This chapter focuses on the underlying mathematics of seismic rays. Seismic waves caused by earthquakes and explosions are used in seismic tomography to create computer-generated, three-dimensional images of Earth's interior. If the Earth had a uniform composition and density, seismic rays would travel in straight lines. However, it is broadly layered, causing seismic rays to be refracted and reflected across boundaries. In order to calculate the speed along the wave's ray path, the time it takes for a seismic wave to arrive at a seismic station from an earthquake needs to be determined. Arrival times of different seismic waves allow scientists to define slower or faster regions deep in the Earth. The chapter first presents the relevant equations for seismic rays before discussing how rays are propagated in a spherical Earth. The Wiechert-Herglotz inverse problem is considered, along with the properties of X in a horizontally stratified Earth.

Horizontal particle velocity and its relation to magnitude in the Western United States

1979 ◽  
Vol 69 (6) ◽  
pp. 2037-2061
Author(s):  
A. F. Espinosa
Keyword(s):  
United States ◽  
Data Base ◽  
San Francisco ◽  
Seismic Waves ◽  
Scaling Law ◽  
Direct Determination ◽  
Strong Motion ◽  
Western United States ◽  
Short Period ◽  
Horizontal Particle

abstract A magnitude (ML) scaling law has been derived from the strong-motion data base of the San Fernando earthquake of February 9, 1971, and the results have been compared with other strong-motion recordings obtained from 62 earthquakes in the Western United States. The relationship derived is ML = 3.21 + 1.35 log10Δ + log10v. An excellent agreement was obtained between the determined ML values in this study and those evaluated by Kanamori and Jennings (1978). This scaling law is applicable to the collected data from 63 earthquakes whose local magnitudes range from about 4.0 to 7.2, recorded at epicentral distances between about 5 to 300 km, and with short-period seismic waves in the range of 0.2 to 3.0 sec. The Long Beach earthquake of 1933, with an ML = 6.3 (PAS) and an ML = 6.43 ± 0.36 as determined by Kanamori and Jennings is in agreement with an ML = 6.49 ± 0.32 obtained in this study. The Imperial Valley earthquake of 1940, with an ML = 6.5 (PAS), compares well with an ML = 6.5 as determined in this study. The Kern County earthquake of 1952, with an ML = 7.2 (BRK), is in fairly good agreement with the ML = 7.0 ± 0.2 obtained in this investigation. This value is significantly lower than the commonly quoted 7.7 value for this event. The San Francisco earthquake of 1957, with an ML = 5.3 (BRK), agrees very well with an ML = 5.3 ± 0.1 as determined in this study. The Parkfield earthquake of 1966 has an ML = 5.8 ± 0.3, which is consistent with the 5.6 (PAS). The procedure developed here is applied to the data base obtained from the Western United States strong-motion recordings. The procedure allows the evaluation of ML for moderate and larger earthquakes from the first integration of the strong-motion accelerograms and allows the direct determination of ML from the scaled amplitudes in a rapid, economical, and accurate manner. It also has allowed for the extension of the trend of the attenuation curve for horizontal particle velocities at distances less than 5 km for different size events.

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