Routine location of T-phase sources in the Pacific

1966 ◽  
Vol 56 (1) ◽  
pp. 109-118 ◽  
Author(s):  
Rockne H. Johnson
Keyword(s):  
Peak Power ◽  
Power Level ◽  
Earthquake Magnitude ◽  
Origin Time ◽  
Arrival Times ◽  
Early Results ◽  
The Pacific ◽  
Least Squares Fit ◽  
The Kuril Islands ◽  
T Phase

abstract A program for the routine location of T-phase sources in the Pacific is described. Data for this program are supplied principally by the Pacific Missile Range hydrophone network. Arrival times and power levels are read at Honolulu for processing by an IBM 7040 computer. The solution for location and origin time is the least-squares fit to all hydrophone arrivals which are weighted according to their distribution in azimuth and their distance from the T-phase source. The velocities for the program are obtained from algebraic functions of latitude and longitude which are based upon shot calibrations and upon hydrographic measurements. A T-phase strength is computed from readings of peak power level in a manner analogous to earthquake magnitude. Early results for the r.m.s. difference between T-phase source locations and the corresponding earthquake epicenters were 0.6° in the Aleutians and 1.1° in the Kuril Islands.

T-phase radiators in the western Aleutians

1968 ◽  
Vol 58 (1) ◽  
pp. 1-10
Author(s):  
Rockne H. Johnson ◽  
Roger A. Norris
Keyword(s):  
Large Volume ◽  
Main Shock ◽  
Source Location ◽  
Earthquake Magnitude ◽  
The Pacific ◽  
Aleutian Arc ◽  
Relationship Of ◽  
T Phase ◽  
The Relationship

abstract The aftershocks of the Rat Islands earthquake of 4 February 1965 provided a large volume of data for processing with a T-phase source location program. Although the earthquake epicenters were somewhat uniformly distributed through the Rat and Near Islands region, the computed T-phase sources were grouped in six clusters along the Aleutian arc. The clusters are considered to represent radiation from distinct sites along the Aleutian Ridge. These sites are probably submarine promontories which, due to their exposure, radiate energy over broader arcs of the Pacific than do intervening regions. The relationship of T-phase strength to earthquake magnitude varied little among these radiators; however, T phases from sources south of the Aleutian trench were significantly weaker. Identification of the arrivals from separate radiators in the signal from the main shock allowed an estimation of the length and velocity of the faulting. The estimate was 500 km and 3.5 km/sec.

scholarly journals Low Frequency Noise Contamination in Fan Model Testing

2008 ◽  
Author(s):  
Clifford A. Brown ◽  
Nicholas A. Schifer
Keyword(s):  
Power Level ◽  
Pressure Ratio ◽  
Jet Noise ◽  
Scale Model ◽  
Frequency Noise ◽  
Fan Noise ◽  
Noise Component ◽  
Least Squares Fit ◽  
Noise Contamination ◽  
The Impact

Aircraft engine noise research and development depends on the ability to study and predict the noise created by each engine component in isolation. The presence of a downstream pylon for a model fan test, however, may result in noise contamination through pylon interactions with the free stream and model exhaust airflows. Additionally, there is the problem of separating the fan and jet noise components generated by the model fan. A methodology was therefore developed to improve the data quality for the 9 × 15 Low Speed Wind Tunnel (LSWT) at the NASA Glenn Research Center that identifies three noise sources: fan noise, jet noise, and rig noise. The jet noise and rig noise were then measured by mounting a scale model of the 9 × 15 LSWT model fan installation in a jet rig to simulate everything except the rotating machinery and in duct components of fan noise. The data showed that the spectra measured in the LSWT has a strong rig noise component at frequencies as high as 3 kHz depending on the fan and airflow fan exit velocity. The jet noise was determined to be significantly lower than the rig noise (i.e. noise generated by flow interaction with the downstream support pylon). A mathematical model for the rig noise was then developed using a multi-dimensional least squares fit to the rig noise data. This allows the rig noise to be subtracted or removed, depending on the amplitude of the rig noise relative to the fan noise, at any given frequency, observer angle, or nozzle pressure ratio. The impact of isolating the fan noise with this method on spectra, overall power level (OAPWL), and Effective Perceived Noise Level (EPNL) is studied.

scholarly journals Technique for solving for microseismic source location parameters based on adaptive particle swarm optimization

2019 ◽  
Author(s):  
Hong-Mei Sun ◽  
Jian-Zhi Yu ◽  
Xing-Li Zhang ◽  
Bing-Guo Wang ◽  
Rui-Sheng Jia
Keyword(s):  
Particle Swarm Optimization ◽  
Wave Velocity ◽  
Least Squares Method ◽  
Particle Swarm ◽  
Pso Algorithm ◽  
P Wave ◽  
Origin Time ◽  
Swarm Optimization ◽  
Arrival Times ◽  
P Wave Velocity

Abstract. An intelligent method is presented for locating microseismic source based on particle swarm optimization (PSO) concept. It eliminates microseismic source locating errors caused by inaccurate velocity model of the earth medium. The method uses as the target of PSO a global minimum of the sum of squared discrepancies between modeled arrival times and measured arrival times. The discrepancies are calculated for all pairs of detectors of a seismic monitoring system, Then, the adaptive PSO algorithm is applied to locate the microseismic source and obtain optimal value of the P-wave velocity. The PSO algorithm adjusts inertia weight, accelerating constants, the maximum flight velocity of particles, and other parameters to avoid the PSO algorithm trapping by local optima during the solution process. The origin time of the microseismic event is estimated by minimizing the sum of squared discrepancies between the modeled arrival times and the measured arrival times. This Sum is calculated using the obtained estimates of the microseismic source coordinates and P-wave velocity. The effectiveness of the PSO algorithm was verified through inversion of a theoretical model and two analyses of actual data from mine blasts in different locations. Compared with the classic least squares method, the PSO algorithm displays faster convergence and higher accuracy of microseismic source positioning. Moreover, there is no need to measure the microseismic wave velocity in advance: the PSO algorithm eliminates the adverse effects caused by error in the P-wave velocity when locating a microseismic source using traditional methods.

P-velocity models of the southern Diablo Range, California, from inversion of earthquake and explosion arrival times

1978 ◽  
Vol 68 (2) ◽  
pp. 357-367
Author(s):  
J. Alan Steppe ◽  
Robert S. Crosson
Keyword(s):  
Linear Increase ◽  
Low Velocity ◽  
Origin Time ◽  
Arrival Times ◽  
Central California ◽  
Velocity Models ◽  
Crustal Model ◽  
Hypocentral Parameters ◽  
Inversion Procedure ◽  
Damped Least Squares

Abstract Velocity models are developed for the region in and around the southern Diablo Range, lying just east of seismically active portions of the San Andreas and Calaveras faults in central California. An iterative damped least-squares inversion procedure is used to simultaneously estimate hypocentral parameters, station delays, and velocities in a horizontally layered crustal model. Arrival times from both earthquakes and explosions of known location and origin time are used as data. The procedure used has the potential to detect low-velocity layers if they exist. The models obtained show a rapid increase in velocity to about 5.5 km/sec at 3 km depth, another rapid increase to about 6.0 km/sec at 6 km depth, and a roughly linear increase below 6 km with the velocity reaching approximately 6.7 km/sec at a depth of 15 km.

Source bias in epicenter determinations

1968 ◽  
Vol 58 (6) ◽  
pp. 1791-1796
Author(s):  
Eugene Herrin ◽  
James Taggart
Keyword(s):  
Upper Mantle ◽  
Significant Source ◽  
Volcanic Island ◽  
Constant Delay ◽  
Origin Time ◽  
Station Corrections ◽  
The Pacific ◽  
Tectonically Active ◽  
Using Data ◽  
Consistent Error

ABSTRACT Epicenter determinations using data from stations at distances greater than 20° from the source make use of standard travel times based on a spherically symmetrical Earth. Lateral inhomogeneities in the upper mantle result in relative delays with respect to the standard times. Delays associated with the end of the up-traveling ray can be handled through the use of station corrections. A constant delay beneath the source can not be easily corrected, but it will result only in errors in origin time. However, if the delay arising beneath the source changes with azimuth, a consistent error, here called source bias, will be present in the estimate of the epicenter. Studies of explosions within continental masses have revealed no significant source bias; however, events on two linear, volcanic island chains in the Pacific (Rat Islands-Aleutians and Hawaii) show significant source bias. Errors arising from this effect may be as large as 12 degree and are most likely to occur with events near tectonically active island chains.

Discussion of “Proposed use of the T phase in tsunami warning systems”*

1951 ◽  
Vol 41 (2) ◽  
pp. 165-167
Author(s):  
L. Don Leet
Keyword(s):  
Dominican Republic ◽  
Pacific Coast ◽  
Sea Water ◽  
Tsunami Warning ◽  
Columbia University ◽  
Warning Systems ◽  
The Pacific ◽  
Short Period ◽  
The Pacific Ocean ◽  
T Phase

Abstract Ewing, Tolstoy, and Press of Columbia University reported that “a striking correlation between the occurrence of a short-period earthquake phase (T phase) traveling through the ocean with the speed of sound in sea water and the occurrence of tsunamis has been observed.” Their statements about the characteristics of T are incorrect in every essential detail. For the Pacific Ocean, they list five tsunami between 1933 and 1946, of which the largest, on April 1, 1946, was generated by an earthquake for which no T was recorded. They neglect to mention the earthquake of January 23, 1938, near Hawaii, which produced the largest T recorded on the Pacific coast to date, but no tsunami. The importance of these outstanding exceptions, errors in reporting the data, and uncertainty concerning the actual number of T phases recorded on the Pacific coast combine to make the evidence for any value of T as a tsunami warning decidedly inconclusive. In the Atlantic, the proposal that T be used as a tsunami warning reduces to an absurdity. Ewing, Tolstoy, and Press state that between 1939 and 1948 “20 Dominican Republic shocks produced T phases,” and that one of them was followed by a definite tsunami. Actually, more than 200 Dominican Republic shocks produced T within that span of years, and many in other Atlantic regions. With one minor tsunami among 200 to 250 T phases, the correlation is not impressive.

scholarly journals Tsunami source area of the 2011 off the Pacific coast of Tohoku Earthquake determined from tsunami arrival times at offshore observation stations

2011 ◽  
Vol 63 (7) ◽  
pp. 809-813 ◽  
Author(s):  
Yutaka Hayashi ◽  
Hiroaki Tsushima ◽  
Kenji Hirata ◽  
Kazuhiro Kimura ◽  
Kenji Maeda
Keyword(s):  
Pacific Coast ◽  
Tohoku Earthquake ◽  
Source Area ◽  
Tsunami Source ◽  
Arrival Times ◽  
The Pacific
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