F-K analysis of NORESS array and single station data to identify sources of near-receiver and near-source scattering

1990 ◽  
Vol 80 (6B) ◽  
pp. 2227-2241
Author(s):  
I. N. Gupta ◽  
C. S. Lynnes ◽  
T. W. McElfresh ◽  
R. A. Wagner
Keyword(s):  
Arrival Time ◽  
Secondary Phase ◽  
Seismic Source ◽  
Polarization Characteristic ◽  
P Waves ◽  
Earthquake Sources ◽  
Power Difference ◽  
Short Period ◽  
Single Station ◽  
Basin Boundaries

Abstract F-k analyses of short-period recordings of both explosion and earthquake sources at the high-frequency NORESS array indicate secondary arrivals from a near-receiver source about 25 to 30 km southwest of the array. Use of residual seismograms, derived by subtracting the beamed record from each array channel, improved the identification of the same scatterer. F-k power difference plots, obtained by subtracting (after normalization) the f-k power versus slowness estimates for the initial P window from those for the latter windows, provided nearly identical results. The secondary seismic source appears to be short-period surface waves, Rg, generated by the scattering of incident P waves in the region of Lake Mjosa, 27 km southwest of NORESS, where there is about 1 km of relief from the bottom of the lake to the top of an adjacent hill. Polarization analysis of an explosion recorded on three-component elements of NORESS also suggested a secondary phase with polarization characteristic of Rg and arrival time and azimuth consistent with those derived from the f-k analysis. Near-source scattering is investigated by f-k analysis of data from reciprocal arrays formed by interchanging the roles of source and receiver. Application to closely spaced Yucca Flat (NTS) shots recorded at several stations provides evidence for Rg → P scattering near the northwestern and other basin boundaries of the Yucca Valley. It seems that deterministic locations of near-receiver P → Rg and near-source Rg → P scattering can be obtained by f-k techniques.

scholarly journals Implementation of Filter Picker Algorithm For Aftershock Identification of Lombok Earthquake 2018

2019 ◽  
Vol 17 (1) ◽  
pp. 25
Author(s):  
A. Ardianto ◽  
Y.M. Husni ◽  
A. D. Nugraha ◽  
M. Muzli ◽  
Z. Zulfakriza ◽  
...  
Keyword(s):  
Arrival Time ◽  
Seismic Station ◽  
Broad Band ◽  
P Wave ◽  
Practical Reasons ◽  
Time Of Arrival ◽  
P Waves ◽  
Short Period ◽  
Minimum Number ◽  
Comparison Of The Results

The ability to identify earthquake events that are consistent, efficient and accurate is increasingly needed along with the increase in the amount of data analyzed. In this paper a filter picker algorithm is implemented to identify aftershock  events and determination of arrival time automatically, especially for the P wave phase. Here modifications are made in determining the uncertainty of arrival time and there are additional criteria in determining the time of arrival used. The additional criteria are that in a certain time span, there are at least 5 stations determined by the time the filter picker arrives. This is done to minimize identification errors due to local noise and other practical reasons, namely the minimum number of stations to determine the location and other seismological analysis. To test the filter picker algorithm, aftershock data from the Lombok earthquake occurred on July 29 (M 6.4), August 5 (M 7), and August 19 (M 6.3 and M 6.9)  2018. The aftershock data were used for 30 days, from August 4, 2018 to September 4, 2018 using local seismic station in Lombok Island. The results of the filter picker algorithm were evaluated by comparing the number of earthquake events detected and the accuracy of determining the P wave arrival time automatically to the results of manually arriving time. In addition, a comparison of the results obtained from a broadband type seismometer with a short period is used to find out how much influence the type of tool has on its performance results. The results of the comparison with the manual arrival time show that more than 85 percent of the results of the automatic arrival time have a difference below 0.2 seconds. Therefore, it can be said that the filter picker algorithm is quite effective for identifying events and determining the arrival time of P waves. In this paper it is also shown that this algorithm can be used for broad band and short period seismometer sensor, even without the prior correction of instruments.

Source inversion of the 1988 Upland, California, earthquake: Determination of a fault plane for a small event

1990 ◽  
Vol 80 (3) ◽  
pp. 507-518 ◽  
Author(s):  
Jim Mori ◽  
Stephen Hartzell
Keyword(s):  
Green Function ◽  
Fault Plane ◽  
Least Squares Method ◽  
Source Area ◽  
Rupture Velocity ◽  
P Waves ◽  
Waveform Data ◽  
Empirical Green Function ◽  
Finite Fault ◽  
Short Period

Abstract We examined short-period P waves to investigate if waveform data could be used to determine which of two nodal planes was the actual fault plane for a small (ML 4.6) earthquake near Upland, California. We removed path and site complications by choosing a small aftershock (ML 2.7) as an empirical Green function. The main shock P waves were deconvolved by using the empirical Green function to produce simple far-field displacement pulses. We used a least-squares method to invert these pulses for the slip distribution on a finite fault. Both nodal planes (strike 125°, dip 85° and strike 221°, dip 40°) of the first-motion focal mechanism were tested at various rupture velocities. The southwest trending fault plane consistently gave better fitting solutions than the southeast-trending plane. We determined a moment of 4.2 × 1022 dyne-cm. The rupture velocity, and thus the source area could not be well resolved, but if we assume a reasonable rupture velocity of 0.87 times the shear wave velocity, we obtain a source area of 0.97 km2 and a stress drop of 38 bars. Choice of a southwest-trending fault plane is consistent with the trend of the nearby portion of the Transverse Ranges frontal fault zone and indicates left-lateral motion. This method provides a way to determine the fault plane for small earthquakes that have no surface rupture and no obvious trend in aftershock locations.

scholarly journals Automated detection and association of surface waves

1994 ◽  
Vol 37 (3) ◽  
Author(s):  
R. G. North ◽  
C. R. D. Woodgold
Keyword(s):  
Surface Waves ◽  
Group Velocity ◽  
Rayleigh Waves ◽  
Arrival Time ◽  
Narrow Band ◽  
Broad Band ◽  
Detection Algorithm ◽  
Automated Detection ◽  
Short Period ◽  
Group Velocities

An algorithm for the automatic detection and association of surface waves has been developed and tested over an 18 month interval on broad band data from the Yellowknife array (YKA). The detection algorithm uses a conventional STA/LTA scheme on data that have been narrow band filtered at 20 s periods and a test is then applied to identify dispersion. An average of 9 surface waves are detected daily using this technique. Beamforming is applied to determine the arrival azimuth; at a nonarray station this could be provided by poIarization analysis. The detected surface waves are associated daily with the events located by the short period array at Yellowknife, and later with the events listed in the USGS NEIC Monthly Summaries. Association requires matching both arrival time and azimuth of the Rayleigh waves. Regional calibration of group velocity and azimuth is required. . Large variations in both group velocity and azimuth corrections were found, as an example, signals from events in Fiji Tonga arrive with apparent group velocities of 2.9 3.5 krn/s and azimuths from 5 to + 40 degrees clockwise from true (great circle) azimuth, whereas signals from Kuriles Kamchatka have velocities of 2.4 2.9 km/s and azimuths off by 35 to 0 degrees. After applying the regional corrections, surface waves are considered associated if the arrival time matches to within 0.25 km/s in apparent group velocity and the azimuth is within 30 degrees of the median expected. Over the 18 month period studied, 32% of the automatically detected surface waves were associated with events located by the Yellowknife short period array, and 34% (1591) with NEIC events; there is about 70% overlap between the two sets of events. Had the automatic detections been reported to the USGS, YKA would have ranked second (after LZH) in terms of numbers of associated surface waves for the study period of April 1991 to September 1992.

Estimating azimuth and slowness from three-component and array stations

1990 ◽  
Vol 80 (6B) ◽  
pp. 1987-1998 ◽  
Author(s):  
Anne Suteau-Henson
Keyword(s):  
Arrival Time ◽  
Dominant Frequency ◽  
Polarization Analysis ◽  
Vertical Array ◽  
Regional Network ◽  
Array Measurements ◽  
Short Period ◽  
Wide Range ◽  
P Type ◽  
Teleseismic Events

Abstract The capabilities of three-component (3-C) and array stations for estimating azimuth and slowness are compared for short-period P-type phases recorded at the NORESS array. For vertical array data, azimuth and slowness estimates are obtained from broadband frequency-wavenumber (f-k) analysis. For 3-C data, polarization analysis is performed. The data processing is automated, using arrival time and dominant frequency information from the NORESS Bulletin. Independent determinations of azimuth and/or slowness, obtained from locations in the NEIS or regional network bulletins, are used as reference estimates. Over 100 events are analyzed, both teleseismic and regional. They were selected from a variety of distances and azimuths, and cover a wide range of signal-to-noise ratios (SNR). The capability of 3-C stations for azimuth and slowness estimation critically depends on SNR. For SNR below a threshold of ∼2, the scatter in the estimates is very large for both parameters, and the slowness of teleseismic events tends to be overestimated. Also, the results are site-dependent within the NORESS array. The array measurements obtained with the broadband f-k method are not significantly affected by noise at the levels of SNR considered. For events with sufficient SNR, both methods compare well, and only a slightly better performance is observed with the f-k method.

scholarly journals Seismic scatterers in the lower mantle near subduction zones

2019 ◽  
Vol 219 (Supplement_1) ◽  
pp. S2-S20 ◽  
Author(s):  
Satoshi Kaneshima
Keyword(s):  
Oceanic Crust ◽  
Lower Mantle ◽  
Subduction Zones ◽  
P Waves ◽  
Waveform Data ◽  
Basaltic Rocks ◽  
Short Period ◽  
Subducted Oceanic Crust ◽  
Conversion Depth ◽  
Seismic Networks

SUMMARY We investigate the global distribution of S-to-P scatterers in the shallow to mid-lower mantle beneath subduction zones, where deep seismicity extends down to the bottom of the upper mantle. By array processing broadband and short period waveform data obtained at seismic networks, we seek anomalous later phases in the P coda within about 15–150 s after direct P waves. The later phases usually arrive along off-great circle paths and significantly later than S-to-P conversion from the ‘660 km’ discontinuity, often show positive slowness anomalies relative to direct P, and do not show a conversion depth that is consistent among nearby events. They are thus adequately regarded as scattered waves, rather than conversion at a global horizontal discontinuity. The S-to-P scattered waves often show amplitudes comparable to ‘S660P’ waves, which indicates that a spatial change in elastic properties by several percent occurs at the scatterers as abruptly as the post-spinel transformation and should arise from compositional heterogeneity. We locate prominent S-to-P scatterers beneath Pacific subduction zones and beneath southern Spain. Nearly half of 137 S-to-P scatterers located in this study and previous studies by the authors are shallower than 1000 km, and the number of scatterers decreases with depth. Scatterers deeper than 1800 km are rare and mostly weak. We examine relations between the locations of the scatterers and recently subducted slabs inferred from seismic tomography. The scatterers of mid-mantle depths, deeper than about 1000 km, are located distant from tomographic slabs. On the other hand, the majority of shallower scatterers are located beneath the slabs rather than near their fastest portions, which would indicate that chemically heterogeneous materials are not extensively entrained within thickened and folded slabs when the slabs impinge on the lower mantle. We also find scatterers near the locations where basaltic rocks of recently subducted oceanic crust are expected to exist, which suggests that oceanic crust is not delaminating when slabs impinge on the lower mantle.

WIDE‐BAND EXTRACTION OF MANTLE P WAVES FROM AMBIENT NOISE

Geophysics ◽  
1964 ◽  
Vol 29 (5) ◽  
pp. 672-692 ◽  
Author(s):  
Milo Backus ◽  
John Burg ◽  
Dick Baldwin ◽  
Ed Bryan
Keyword(s):  
Ambient Noise ◽  
Wide Band ◽  
P Wave ◽  
Cumberland Plateau ◽  
P Waves ◽  
Single Output ◽  
Short Period ◽  
Multichannel Filtering ◽  
On Line ◽  
Element Array

The spatial correlation characteristics of ambient short‐period (0.5 to 5 cps) noise at Ft. Sill, Oklahoma, and on the Cumberland Plateau in Tennessee were investigated on “permanent” arrays with 3–4 kilometer diameter. Dominant ambient noise at the two locations is spatially organized, and to first order may be treated as a combination of seismic propagating wave trains. At the Tennessee location noise energy above one cps is dominantly propagating with velocities from 3.5 to 4.5 km/sec, and must be carried in deeply trapped, high‐order modes. Generalized multichannel filtering (Burg) can be used to preserve a large class of mantle P‐wave signals, wide‐band, in a single output trace, while at the same time specifically rejecting ambient noise on the basis of its organization. Results of generalized multichannel filtering applied on‐line at the nineteen‐element array in Tennessee and applied off‐line are discussed.

scholarly journals Comparative Measurements of Local Seismic Rotations by Three Independent Methods

Sensors ◽  
2020 ◽  
Vol 20 (19) ◽  
pp. 5679
Author(s):  
Johana Brokešová ◽  
Jiří Málek
Keyword(s):  
Seismic Source ◽  
Medium Size ◽  
Period Range ◽  
Small Aperture ◽  
Technical Problems ◽  
Rotation Rates ◽  
Active Experiment ◽  
Short Period ◽  
Order Of Magnitude ◽  
The Given

A comparative active experiment that is aimed at collocated measurement of seismic rotation rates along three orthogonal axes by means of three different methods is described. The rotation rates in a short-period range of 6–20 Hz were obtained using three different methods: the 6C Rotaphone sensor system developed by the authors, the commercial R-1 rotational sensor by Eentec, and a small-aperture array of twelve standard velocigraphs in a rectangular arrangement. Those three methods are compared and discussed in detail. A medium-size quarry blast was used as a seismic source. At a distance of approximately 240 m, the rotation rates reached an amplitude of the order of magnitude of 10−4–10−5 rad/s. The array derived rotation rates displayed serious limitations, as clearly documented. The R-1 instruments have shown certain technical problems that partly limit their applicability. The measured rotation rates were compared to the relevant acceleration components according to rotation-to-translation relations. Out of all the three methods, the records best matching the acceleration components were made by Rotaphone. The experiment also revealed that rotation rates in the given short-period range noticeably changed over a distance as short as 2 m.

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