Arrival times of P waves and upper mantle structure

1964 ◽  
Vol 54 (2) ◽  
pp. 727-736
Author(s):  
Eysteinn Tryggvason
Keyword(s):  
Standard Error ◽  
Upper Mantle ◽  
P Wave ◽  
P Waves ◽  
Arrival Times ◽  
P Wave Velocity ◽  
Upper Mantle Structure ◽  
The Mean ◽  
The Difference ◽  
Mantle Velocity

ABSTRACT Residuals of arrival times of P waves, as given in the International Seismological Summary for Kiruna, Sweden, Reykjavik, Iceland, and Scoresbysund, Greenland, were studied in order to detect upper mantle anomalies. The Kiruna arrivals were systematically too early, with a mean residual of −1.4 seconds, while the mean Reykjavik residual was +1.3 seconds. The difference in mean residual was 2.7 seconds with a standard error of about 0.5 second. The mean residual at Scoresbysund was −0.4 second. It is assumed that there is a depth D below which the mantle is homogeneous. The difference in mean residuals at the stations is assumed to be caused by different wave velocities at depths less than D in the vicinities of the stations. If it is assumed that the P-wave velocity in the upper mantle is constant down to a depth D below each station, this depth can be computed. This velocity is known from other data to be 8.36 km/sec below Kiruna and 7.4 km./sec. below Reykjavik. If only earthquakes at distances from 20° to 39° were used, D is determined to be 246 ± 36 km. (standard error). Earthquakes at distances 40° to 59° give D = 177 ± 25 km., at distances 60° to 79° give D = 234 ± 14 km., and at distances 80° to 99° give D = 281 ± 20 km. The most probable value of D is thus about 240 km. below the earth's surface, with a standard error of about 40 km. In the vicinity of Scoresbysund the upper mantle velocity is found to be about 8.0 km./sec., using the same assumption.

A fall in P-wave velocity before the Gisborne, New Zealand, earthquake of 1966

1974 ◽  
Vol 64 (5) ◽  
pp. 1501-1507 ◽  
Author(s):  
D. J. Sutton
Keyword(s):  
New Zealand ◽  
Wave Velocity ◽  
Significant Variation ◽  
Arrival Time ◽  
P Wave ◽  
Time Interval ◽  
P Waves ◽  
Arrival Times ◽  
P Wave Velocity ◽  
Seismograph Station

Abstract A fall in P-wave velocity before the Gisborne earthquake of March 4, 1966 is indicated by arrival-time residuals of P waves from distant earthquakes recorded at the Gisborne seismograph station. Residuals were averaged over 6-month intervals from 1964 to 1968 and showed an increase of about 0.5 sec, implying later arrival times. The change began about 480 days before the earthquake. This precursory time interval is about that expected for an earthquake of this magnitude (ML = 6.2), but unlike most other reported instances, there was no obvious delay between the return of the velocity to normal and the occurrence of the earthquake. Similar analyses were carried out over the same period for two other New Zealand seismograph stations; at Karapiro there was no significant variation in mean residuals, and at Wellington the scatter was too large for the results to be meaningful. The Gisborne earthquake had a focus in the lower crust, about 25 km deep and was deeper than other events for which such precursory drops in P-wave velocity have been reported.

Upper Mantle Structure in Southern Saskatchewan and Western Manitoba from Project Edzoe

1975 ◽  
Vol 12 (12) ◽  
pp. 2134-2144 ◽  
Author(s):  
Allan Bates ◽  
D. H. Hall
Keyword(s):  
Upper Mantle ◽  
Linear Increase ◽  
P Wave ◽  
Mantle Structure ◽  
Low Velocity ◽  
Wave Velocities ◽  
P Wave Velocity ◽  
Upper Mantle Structure ◽  
Chemical Explosions ◽  
Velocity Zone

A line of eight recording sites in southern Saskatchewan and Manitoba, with ranges from 793 to 1284 km, recorded a series of chemical explosions in Greenbush Lake, British Columbia, as part of Project Edzoe in 1969.It is found that travel-times fall into two branches. The first branch is interpreted as representing the effect of a linear increase of P wave velocity, increasing from 8.10 km/s at the top of the mantle, with a gradient of 0.0017 s−1. The second branch indicates a rapid increase of gradient occurring somewhere between depths of 120 km and 150 km. Amplitude studies suggest, in the absence of complete triplication, a zone of low velocity gradient beneath the rapid increase. The presence or absence of a low velocity zone was not indicated in the data.Previous long-range refraction surveys indicate that a similar gradient in velocity also occurs beneath the Superior province of the Canadian shield, and that P-wave velocities are lowest at its center, reaching higher values at its edges.

A simple model of the crust and upper mantle in central Chile

1973 ◽  
Vol 63 (3) ◽  
pp. 819-825
Author(s):  
L. Chuaqui
Keyword(s):  
Wave Velocity ◽  
Upper Mantle ◽  
Structural Parameters ◽  
P Wave ◽  
S Wave ◽  
Crust And Upper Mantle ◽  
Central Chile ◽  
Arrival Times ◽  
P Wave Velocity ◽  
Wave Arrival

abstract A simplified model of the crust and upper mantle of central Chile is developed with P- and S-wave arrival times and is compared with previous gravimetric work on the area. The following structural parameters were determined: crustal P-wave velocity, upper mantle P-wave velocity, crustal thickness and orientation of the plane separating crust and upper mantle. The model obtained here agrees well with those calculated in the gravimetric study.

UPPER MANTLE STRUCTURE IN CANADA FROM SEISMIC OBSERVATIONS USING CHEMICAL EXPLOSIONS

1967 ◽  
Vol 4 (5) ◽  
pp. 961-975 ◽  
Author(s):  
K. G. Barr
Keyword(s):  
Wave Velocity ◽  
Upper Mantle ◽  
Velocity Structure ◽  
P Wave ◽  
Hudson Bay ◽  
S Wave ◽  
Low Velocity ◽  
P Wave Velocity ◽  
Upper Mantle Structure ◽  
Chemical Explosions

Long-range seismic observations at the standard Canadian seismic stations, from chemical explosions in Hudson Bay and Lake Superior, are used to derive a P-wave velocity structure for the upper mantle. The coordinates of observed cusps are used to define the structural discontinuities. These discontinuities are at depths of 126 and 366 km, which agree closely with the depths of the S-wave velocity discontinuities deduced from surface-wave observations. The observations do not require a low velocity layer in the upper mantle.

scholarly journals P- waves reflected from the "20" discontinuity" beneath the Mediterranean region

2010 ◽  
Vol 28 (1) ◽  
Author(s):  
A BOTTARI ◽  
B. FEDERICO
Keyword(s):  
Mediterranean Area ◽  
P Wave ◽  
Travel Times ◽  
P Waves ◽  
First Order ◽  
P Wave Velocity ◽  
Different Depths ◽  
The Mediterranean ◽  
Regional Character ◽  
Order Discontinuity

The observed travel-times of the P-waves for twenty shallow, intermediate, and deep earthquakes, with epicenters in the Mediterranean area, are used in order to analyze some characteristics of the upper mantle. A first- order discontinuity, identifiable as the "20° discontinuity", is found at a depth of 505 ± 16 km in the area underneath the Mediterranean basin. The velocity contrast is equal to 12% (above T'= 8.9 km/sec; below V= 9.97 km/sec). Assuming that this discontinuity gives rise to reflected P-waves (PdP), the travel times of these waves are calculated for various hypocentral depths. The observation of impulses identified as PdP on the seismograms of Messina supports this hypothesis. This result and its implications are discussed in the contest of the conclusions of various authors who locate a P-wave velocity-discontinuity at different depths between 400 and 580 km. Finally, particular emphasis is given to the regional character of the analyzed structures in question.

Seismic analysis of the 7 January 1998 Chemical plant explosion at Kean Canyon, Nevada

1999 ◽  
Vol 89 (4) ◽  
pp. 938-945 ◽  
Author(s):  
Gene A. Ichinose ◽  
Kenneth D. Smith ◽  
John G. Anderson
Keyword(s):  
Seismic Analysis ◽  
Correlation Method ◽  
Chemical Safety ◽  
P Waves ◽  
Arrival Times ◽  
Chemical Company ◽  
Optimal Separation ◽  
The Difference ◽  
Possible Cause

Abstract An accident at the Sierra Chemical Company Kean Canyon plant, 16 km east of Reno, Nevada, resulted in two explosions 3.52 sec apart that devastated the facility. An investigation into a possible cause for the accident required the determination of the chronological order of the explosions. We resolved the high-precision relative locations and chronology of the explosions using a cross-correlation method applied to both seismic and air waves. The difference in relative arrival times of air waves between the explosions indicated that the first explosion occurred at the northern site. We then determined two station centroid separations between explosions, which average about 73 m with uncertainties ranging from ± 17 to 41 m depending on the alignment of station pairs. We estimated a centroid separation of 80 m using P waves with a larger uncertainty of ± 340 m. We performed a grid search for an optimal separation and the azimuth by combining air-wave arrivals from three station pairs. The best solution for the relative location of the second explosion is 73.2 m S35°E from the first explosion. This estimate is well within the uncertainties of the survey by the U.S. Chemical Safety and Hazard Investigation Board (CSB). The CSB reported a separation of approximately 76.2 m S33°E. The spectral amplitudes of P waves are 3 to 4 times higher for the second explosion relative to the first explosion, but the air waves have similar spectral amplitudes. We suggest that this difference is due to the partitioning of energy between the ground and air caused by downward directivity at the southern explosion, and upward directivity at the northern explosion. This is consistent with the absence of a crater for the first explosion and a 1.8-m-deep crater for the second explosion.

The Heritage Stone of Nossa Senhora de Guadalupe Church, Mouçós, North of Portugal: Characterisation and Glyptography

2021 ◽  
Author(s):  
David Freire-Lista ◽  
Bruno Campos ◽  
Patricia Moreira da Costa
Keyword(s):  
Water Absorption ◽  
Bulk Density ◽  
Wave Velocity ◽  
Effective Porosity ◽  
P Wave ◽  
Building Stones ◽  
Thin Sections ◽  
P Wave Velocity ◽  
The Mean ◽  
The Church

<p>Granite is the most important building stone in the north of Portugal. The importance of the stones in this region is evidenced by the pre-Roman roots Mor (r), Mur (r) and Mour of place names such as Montemuro, Moreiras, Mouçós, and Mourelhe. These roots indicate the existence of building stones used since ancient times in these places.</p><p>The quarries of the main building stones of historical buildings were generally in the vicinity of the buildings. Formerly, stonemasons carved mason's marks on ashlars. The mason's marks are lapidary signs to indicate the work carried out by each one. The mason's marks are generally symbolised by the initial of the stonemason's name. They are often found on dressed stones in buildings and in other public structures.</p><p>Nossa Senhora de Guadalupe church of Mouçós (possibly 16<sup>th</sup> century) has typical characteristics from the late Romanesque. It is located in Vila Real (North of Portugal). It is made up of three volumes: a single nave, a lower rectangular apse, and a sacristy attached to the apse. The exterior of this church is preserved almost unaltered in its original state. Each of the granite ashlars that make up this church has a mason's mark in the center of its face.</p><p>The mason's marks of the church have been identified; all the ashlars with visible mason's marks have been mapped, and a glyptographic study has been carried out. This has made it possible to calculate the number of stonemasons that worked in the construction of the church and the number of ashlars that were transported in each carriage, and to determine the construction phases of the church.</p><p>Eight cubic samples have been cut to calculate the granite’s hydric properties (effective porosity, water absorption and bulk density) according to UNE-EN:1936. Ultrasound wave velocity was measured according to UNE-EN:14579. Furthermore, three thin sections have been made to characterise the granite petrographically under a polarisation microscope Leica DM-4500-P. A mosaic of photomicrographs has been made to evaluate the petrographic properties.</p><p>There are six main types of mason's marks in Nossa Senhora de Guadalupe Church. All quarrymen extracted the stones from the same quarry, or from nearby quarries. The mean effective porosity of the building granite is 3.2%±0.3, and the mean water absorption is 1.2%±0.1. Its mean bulk density is 2566 kg/m<sup>3</sup>±61.0 and its ultrasound P wave velocity is 2920 m/s±98.3.</p><p>The mason's marks are preserved because of the excellent petrographic and petrophysical properties of Mouçós granite. Further, Nossa Senhora de Guadalupe church was protected with lime plaster during the past centuries, and the plaster was not removed with the projection of abrasive particles.</p><p>The use of analytical techniques such as petrography, ultrasonic P wave velocity and the determination of hydric properties will guarantee the quality and durability of a sustainable restoration.</p><p>The historical quarries, forms of traditional stone extraction and uses of Mouçós granite constitute a heritage that must be safeguarded.</p><p>Acknowledgements: The Fundação para a Ciência e a Tecnologia (FCT) of Portugal. CEECIND/03568/2017.</p>

P-wave travel times from shallow earthquakes recorded in India and inferred upper mantle structure

1968 ◽  
Vol 58 (6) ◽  
pp. 1879-1897
Author(s):  
K. L. Kaila ◽  
P. R. Reddy ◽  
Hari Narain
Keyword(s):  
Upper Mantle ◽  
P Wave ◽  
Mantle Structure ◽  
Travel Times ◽  
The North ◽  
Shallow Earthquakes ◽  
Upper Mantle Structure ◽  
Wave Travel ◽  
Excess Value ◽  
Velocity Changes

ABSTRACT P-wave travel times of 39 shallow earthquakes and three nuclear explosions with epicenters in the North in Himalayas, Tibet, China and USSR as recorded in Indian observatories have been analyzed statistically by the method of weighting observations. The travel times from Δ = 2° to 50° can be represented by four straight line segments indicating abrupt velocity changes around 19°, 22° and 33° respectively. The P-wave velocity at the top of the mantle has been found to be 8.31 ± 0.02 km/sec. Inferred upper mantle structure reveals three velocity discontinuities in the upper mantle at depths (below the crust) of 380 ± 20, 580 ± 50 and 1000 ± 120 km with velocities below the discontinuities as 9.47 ± 0.06, 10.15 ± 0.07 and 11.40 ± 0.08 km/sec respectively. The J-B residuals up to Δ = 19° are mostly negative varying from 1 to 10 seconds with a dependence on Δ values indicating a different upper mantle velocity in the Himalayan region as compared to that used by Jeffreys-Bullen in their tables (1940). Between 19° to 33° there is a reasonably good agreement between the J-B curve and the observation points. From Δ = 33° to 50° the J-B residuals are mostly positive with an average excess value of about 4 sec.

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