scholarly journals Separating the scattered wavefield from teleseismic P using curvelets on the long beach array data set

2019 ◽  
Vol 220 (2) ◽  
pp. 1112-1127
Author(s):  
Jia Zhang ◽  
Charles A Langston
Keyword(s):  
Wave Propagation ◽  
Signal To Noise Ratio ◽  
Spherical Wave ◽  
Curvelet Transform ◽  
Structural Heterogeneity ◽  
Seismic Array ◽  
P Wave ◽  
Long Beach ◽  
Data Set ◽  
Array Data

SUMMARY A dense seismic array, composed of over 5000 stations with an average spacing close to 120 m was deployed in Long Beach, CA, by NodalSeismic and Signal Hill Petroleum as part of a survey associated with the Long Beach oilfield. Among many interesting wave propagation effects that have been reported by others, we observe that the coda of teleseismic P waves display waves caused by obvious local scattering from the Signal Hill popup structure between strands of the Newport-Inglewood fault. The density of the seismic array allows space-based methods, such as the Curvelet transform, to be investigated to separate the teleseismic and local scattered wavefields. We decompose a synthetic wavefield composed of a teleseismic plane wave and local scattered spherical wave in the curvelet domain to test the plausibility of our curvelet analysis and then apply the technique to the Long Beach array data set. Background noise is removed by a soft thresholding method and a declustering technique is applied to separate the teleseismic and local scattered wavefield in the curvelet domain. Decomposed results illustrate that the signal-to-noise ratio of the teleseismic P wave can be significantly improved by curvelet analysis. The scattered wavefield is composed of locally propagating Rayleigh waves from the pop-up structure and from the Newport Inglewood fault itself. Observing the wavefield both in space and time clearly improves understanding of wave propagation complexities due to structural heterogeneity.

P-wave backazimuth anomalies observed by a small-aperture seismic array at Pinyon Flat, southern California: Implications for structure and source location

1996 ◽  
Vol 86 (2) ◽  
pp. 470-476 ◽  
Author(s):  
Cheng-Horng Lin ◽  
S. W. Roecker
Keyword(s):  
Southern California ◽  
Seismic Array ◽  
P Wave ◽  
Small Aperture ◽  
Data Set ◽  
Single Interface ◽  
Seismic Networks ◽  
Dense Seismic Array ◽  
Beamforming Technique

Abstract Seismograms of earthquakes and explosions recorded at local, regional, and teleseismic distances by a small-aperture, dense seismic array located on Pinyon Flat, in southern California, reveal large (±15°) backazimuth anomalies. We investigate the causes and implications of these anomalies by first comparing the effectiveness of estimating backazimuth with an array using three different techniques: the broadband frequency-wavenumber (BBFK) technique, the polarization technique, and the beamforming technique. While each technique provided nearly the same direction as a most likely estimate, the beamforming estimate was associated with the smallest uncertainties. Backazimuth anomalies were then calculated for the entire data set by comparing the results from beamforming with backazimuths derived from earthquake locations reported by the Anza and Caltech seismic networks and the Preliminary Determination of Epicenters (PDE) Bulletin. These backazimuth anomalies have a simple sinelike dependence on azimuth, with the largest anomalies observed from the southeast and northwest directions. Such a trend may be explained as the effect of one or more interfaces dipping to the northeast beneath the array. A best-fit model of a single interface has a dip and strike of 20° and 315°, respectively, and a velocity contrast of 0.82 km/sec. Application of corrections computed from this simple model to ray directions significantly improves locations at all distances and directions, suggesting that this is an upper crustal feature. We confirm that knowledge of local structure can be very important for earthquake location by an array but also show that corrections computed from simple models may not only be adequate but superior to those determined by raytracing through smoothed laterally varying models.

scholarly journals Analysis of the Main Factors Influencing the Dominant Frequency of Blast Vibration

2019 ◽  
Vol 2019 ◽  
pp. 1-17 ◽  
Author(s):  
Da Liu ◽  
Wenbo Lu ◽  
Yijia Liu ◽  
Ming Chen ◽  
Peng Yan ◽  
...  
Keyword(s):  
Wave Propagation ◽  
Peak Velocity ◽  
Spherical Wave ◽  
Dominant Frequency ◽  
Vertical Vibration ◽  
P Wave ◽  
Blasting Vibration ◽  
Radial Vibration ◽  
Factors Influencing ◽  
Main Factors

At present, the study on the dominant frequency of blasting vibration is still a worldwide problem. Compared with the mature research on the particle peak velocity of blasting vibration, the researches on the dominant frequency of blasting vibration are much less. In this paper, by analyzing the main influencing factors of the dominant frequency, an attenuation equation of the dominant frequency induced by blasting vibration has been proposed by dimensional analysis combined with the theory of radial spherical wave propagation. The proposed equation is applied to the fitting analysis on the dominant frequency measured in Zhoushan Green Petrochemical Base in China, which has obtained a favorable fitting correlation. Based on the fitting analysis, it has found that the correlation coefficient of radial vibration obtained by the proposed equation is higher than that of vertical vibration, which is resulted from the reason that the vibration in vertical is considered to be influenced most by the R-wave on the ground and perceived to be quite different from the radial vibration affected by P-wave. In generally, different components of blasting waves will affect the attenuation of dominant frequency.

Aftershock Sequence of the 2018 Mw 6.4 Hualien Earthquake in Eastern Taiwan from a Dense Seismic Array Data Set

2018 ◽  
Vol 90 (1) ◽  
pp. 60-67 ◽  
Author(s):  
Hao Kuo‐Chen ◽  
Zhuo‐Kang Guan ◽  
Wei‐Fang Sun ◽  
Pei‐Yu Jhong ◽  
Dennis Brown
Keyword(s):  
Aftershock Sequence ◽  
Seismic Array ◽  
Data Set ◽  
Array Data ◽  
Dense Seismic Array

The stability of rms Lg measurements and their potential for accurate estimation of the yields of Soviet underground nuclear explosions

1990 ◽  
Vol 80 (6B) ◽  
pp. 2106-2126
Author(s):  
Roger A. Hansen ◽  
Frode Ringdal ◽  
Paul G. Richards
Keyword(s):  
Soviet Union ◽  
Signal To Noise Ratio ◽  
Test Site ◽  
P Wave ◽  
Accurate Estimation ◽  
Seismic Stations ◽  
Array Data ◽  
Underground Nuclear Explosions ◽  
Nuclear Explosions ◽  
Single Station

Abstract Data on underground nuclear explosions have recently become available from modern digital seismic stations installed within the Soviet Union and China. Observations of root mean square (rms) Lg-wave signals for Soviet underground nuclear explosions at the Shagan River Test Site in East Kazakhstan show that the relative amplitudes of the rms signals at stations in Norway, the USSR, and China are very similar for different explosions, the standard deviation of the differences being only about 0.03 in logarithmic units (i.e., magnitude units). This is consistent with earlier observations comparing NORSAR and Graefenberg array data, and the observed scatter is significantly lower than has been reported for Lg data from Nevada Test Site explosions. In view of the excellent correspondence found by Nuttli (1986) and Patton (1988) for Lg versus yield at Nevada, this indicates that rms Lg has a potential for yield estimation with very high accuracy at Shagan River. Our study has shown that: (a) selected stations in the USSR and China, situated at regional distances, provide a much improved signal-to-noise ratio of the Lg phase for events at Shagan River, as compared to NORSAR array data; (b) the scaling of rms Lg amplitudes between different-sized events recorded at the same single station site appears to be consistent with that of NORSAR, indicating a remarkable degree of precision in single station measurements of Lg signal; (c) rms Lg amplitude measurements for the best of these stations may be made at 1.5 to 2.0 magnitude units lower than at NORSAR or Graefenberg, allowing a much lower threshold for Lg-based yield determination; and (d) the P-wave detection capabilities of these single stations do not match those of the NORESS and ARCESS arrays; thus, teleseismic signals continue to be important for detection of small nuclear explosions. Our conclusion is that Lg signals appear to provide an excellent basis for supplying estimates of the yields of nuclear explosions even down to below 1 kt when such signals are recorded at high-quality, digital in-country seismic stations, and when calibrated by access to independent (nonseismic) yield information for a few nuclear explosions at the test sites of interest. In the context of monitoring a low-yield threshold test ban treaty, it will, in addition, be important to take into consideration various environmental conditions in the testing area, such as the possible presence of cavities, and to devise appropriate procedures for on-site observations in this regard.

scholarly journals Recording seismic reflections using rigidly interconnected geophones

Geophysics ◽  
2001 ◽  
Vol 66 (6) ◽  
pp. 1838-1842 ◽  
Author(s):  
C. M. Schmeissner ◽  
K. T. Spikes ◽  
D. W. Steeples
Keyword(s):  
Wave Propagation ◽  
Data Acquisition ◽  
Seismic Reflection ◽  
Spatial Sampling ◽  
P Wave ◽  
Signal Distortion ◽  
Reflection And Refraction ◽  
First Arrival ◽  
The Cost ◽  
Seismic Reflections

Ultrashallow seismic reflection surveys require dense spatial sampling during data acquisition, which increases their cost. In previous efforts to find ways to reduce these costs, we connected geophones rigidly to pieces of channel iron attached to a farm implement. This method allowed us to plant the geophones in the ground quickly and automatically. The rigidly interconnected geophones used in these earlier studies detected first‐arrival energy along with minor interfering seismic modes, but they did not detect seismic reflections. To examine further the feasibility of developing rigid geophone emplacement systems to detect seismic reflections, we experimented with four pieces of channel iron, each 2.7 m long and 10 cm wide. Each segment was equipped with 18 geophones rigidly attached to the channel iron at 15‐cm intervals, and the spikes attached to all 18 geophones were pushed into the ground simultaneously. The geophones detected both refracted and reflected energy; however, no significant signal distortion or interference attributable to the rigid coupling of the geophones to the channel iron was observed in the data. The interfering seismic modes mentioned from the previous experiments were not detected, nor was any P‐wave propagation noted within the channel iron. These results show promise for automating and reducing the cost of ultrashallow seismic reflection and refraction surveys.

Source dynamics of the 1979 Imperial Valley earthquake from near-source observations (of ground acceleration and velocity)

1982 ◽  
Vol 72 (6A) ◽  
pp. 1957-1968
Author(s):  
Mansour Niazi
Keyword(s):  
Particle Acceleration ◽  
Particle Velocity ◽  
High Frequency ◽  
Observation Point ◽  
P Wave ◽  
Imperial Valley ◽  
Ground Acceleration ◽  
Data Set ◽  
Ground Shaking ◽  
Fault Surface

abstract Two sets of observations obtained during the 15 October 1979 Imperial Valley earthquake, MS 6.9, are presented. The data suggest different dynamic characteristics of the source when viewed in different frequency bands. The first data set consists of the observed residuals of the horizontal peak ground accelerations and particle velocity from predicted values within 50 km of the fault surface. The residuals are calculated from a nonlinear regression analysis of the data (Campbell, 1981) to the following empirical relationships, PGA = A 1 ( R + C 1 ) − d 1 , PGV = A 2 ( R + C 2 ) − d 2 in which R is the closest distance to the plane of rupture. The so-calculated residuals are correlated with a positive scalar factor signifying the focusing potential at each observation point. The focusing potential is determined on the basis of the geometrical relation of the station relative to the rupture front on the fault plane. The second data set consists of the acceleration directions derived from the windowed-time histories of the horizontal ground acceleration across the El Centro Differential Array (ECDA). The horizontal peak velocity residuals and the low-pass particle acceleration directions across ECDA require the fault rupture to propagate northwestward. The horizontal peak ground acceleration residuals and the high-frequency particle acceleration directions, however, are either inconclusive or suggest an opposite direction for rupture propagation. The inconsistency can best be explained to have resulted from the incoherence of the high-frequency radiation which contributes most effectively to the registration of PGA. A test for the sensitivity of the correlation procedure to the souce location is conducted by ascribing the observed strong ground shaking to a single asperity located 12 km northwest of the hypocenter. The resulting inconsistency between the peak acceleration and velocity observations in relation to the focusing potential is accentuated. The particle velocity of Delta Station, Mexico, in either case appears abnormally high and disagrees with other observations near the southeastern end of the fault trace. From the observation of a nearly continuous counterclockwise rotation of the plane of P-wave particle motion at ECDA, the average rupture velocity during the first several seconds of source activation is estimated to be 2.0 to 3.0 km/sec. A 3 km upper bound estimate of barrier dimensions is tentatively made on the basis of the observed quasiperiodic variation of the polarization angles.

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