scholarly journals Measuring and crust-correcting finite-frequency travel time residuals – application to southwestern Scandinavia

2015 ◽  
Vol 7 (3) ◽  
pp. 1909-1939
Author(s):  
M. L. Kolstrup ◽  
V. Maupin
Keyword(s):  
Data Processing ◽  
Travel Time ◽  
Cross Correlation ◽  
Correlation Method ◽  
Ray Theory ◽  
Finite Frequency ◽  
S Wave ◽  
Low Velocity ◽  
Arrival Times ◽  
S Waves

Abstract. We present a data processing routine to compute relative finite-frequency travel time residuals using a combination of the Iterative Cross-Correlation and Stack (ICCS) algorithm and the MultiChannel Cross-Correlation method (MCCC). The routine has been tailored for robust measurement of P and S wave travel times in several frequency bands and for avoiding cycle-skipping problems at the shortest periods. We also investigate the adequacy of ray theory to calculate crustal corrections for finite-frequency regional tomography in normal continental settings with non-thinned crust. We find that ray theory is valid for both P and S waves at all relevant frequencies as long as the crust does not contain low-velocity layers associated with sediments at the surface. Reverberations in the sediments perturb the arrival times of the S waves and the long-period P waves significantly, and need to be accounted for in crustal corrections. The data processing routine and crustal corrections are illustated using data from a network in southwestern Scandinavia.

scholarly journals Measuring and crust-correcting finite-frequency travel time residuals – application to southwestern Scandinavia

Solid Earth ◽  
2015 ◽  
Vol 6 (4) ◽  
pp. 1117-1130 ◽  
Author(s):  
M. L. Kolstrup ◽  
V. Maupin
Keyword(s):  
Data Processing ◽  
Travel Time ◽  
Cross Correlation ◽  
Correlation Method ◽  
Ray Theory ◽  
Finite Frequency ◽  
S Wave ◽  
Low Velocity ◽  
Arrival Times ◽  
S Waves

Abstract. We present a data-processing routine to compute relative finite-frequency travel time residuals using a combination of the Iterative Cross-Correlation and Stack (ICCS) algorithm and the Multi-Channel Cross-Correlation method (MCCC). The routine has been tailored for robust measurement of P- and S-wave travel times in several frequency bands and for avoiding cycle-skipping problems at the shortest periods. We also investigate the adequacy of ray theory to calculate crustal corrections for finite-frequency regional tomography in normal continental settings with non-thinned crust. We find that ray theory is valid for both P and S waves at all relevant frequencies as long as the crust does not contain low-velocity layers associated with sediments at the surface. Reverberations in the sediments perturb the arrival times of the S waves and the long-period P waves significantly, and need to be accounted for in crustal corrections. The data-processing routine and crustal corrections are illustrated using data from a~network in southwestern Scandinavia.

Reliability evaluation of volcanic tremor source location determination using cross-correlation functions

2019 ◽  
Author(s):  
Theodorus Permana ◽  
Takeshi Nishimura ◽  
Hisashi Nakahara ◽  
Eisuke Fujita ◽  
Hideki Ueda
Keyword(s):  
Travel Time ◽  
Correlation Functions ◽  
Cross Correlation ◽  
Vertical Component ◽  
Volcanic Tremor ◽  
Source Location ◽  
Arrival Times ◽  
S Waves ◽  
Location Determination ◽  
Cross Correlation Analysis

Summary Source location determination of volcanic tremor has been a challenge in seismology due to the waveform complexity and difficulties in reading P- and S-wave arrival times. We present a method for locating volcanic tremor recorded at a seismic network distributed around a volcano. The method combines the source-scanning algorithm and cross-correlation analysis. Tremor records are processed using a technique adopted from ambient seismic interferometry to obtain stacked cross-correlation functions (CCFs) for all station pairs, which are expected to show high amplitudes at the lag time that corresponds to the travel time difference between the stations. The best seismic source location is determined from the maximum of the sum of envelope amplitudes of CCFs at predicted travel time differences between all pairs of stations. This method does not compute theoretical amplitudes, assume an initial hypocenter location, or measure the arrival times. To quantitatively evaluate the accuracy of the location determination, we examine the method by using the vertical component seismic data of volcano-tectonic (VT) earthquakes recorded at six seismic stations at Izu-Oshima volcano. The VTs have been previously located by using arrival times of P- and S-waves, and the hypocenters are used as the reference for evaluation and error estimation of the method. The results show that the misfit, which is the distance between our estimated sources and the references, is about 2 km or less when using CCFs at the frequency band of 4–16 Hz which contains the dominant frequencies of direct S-waves. To test whether the method can be used for volcanic tremor, we simulate the tremors by combining the observed VTs that occurred randomly in time in a localized region. The simulated tremors are determined with location errors of approximately 1 km or less, when the sources of VTs are located within a distance of 1 km and CCFs are calculated for a minimum data length of about 2 minutes. The volcanic tremor location method we present here can be used as an alternative tool for volcano monitoring, especially to locate tremors and seismic events with no clear phase arrival.

scholarly journals Constraints on temporal variations in velocity near Anza, California, from analysis of similar event pairs

1995 ◽  
Vol 85 (1) ◽  
pp. 194-206 ◽  
Author(s):  
Jennifer S. Haase ◽  
Peter M. Shearer ◽  
Rick C. Aster
Keyword(s):  
Travel Time ◽  
Seismic Velocity ◽  
Correlation Method ◽  
Temporal Variations ◽  
P Wave ◽  
Seismic Gap ◽  
S Wave ◽  
Arrival Times ◽  
Time Separation ◽  
Time Changes

Abstract Similar earthquake pairs recorded by the Anza Seismic Network in southern California are used as repeatable sources to place an upper limit on temporal changes in seismic velocity which occurred in the vicinity of the Anza seismic gap in the last 9 yr. Relative arrival times for each pair of events are found using a cross-correlation method and relative locations are calculated to verify that the pairs have nearly identical hypocenters. The time separation between events in these pairs varies from less than a day to almost 7 yr. The long-term changes in seismic travel times, as measured from the pairs with the longest time separation, are not significantly greater than the noise level estimated from the short-time-separation event pairs. Almost all P-wave paths show less than 0.06% (0.007 sec) change in travel time and all S-wave paths have less than 0.03% (0.004 sec) change. Sensitivity tests place an upper bound on travel-time changes that could be compensated by hypocenter mislocation at 0.2%. There is no evidence that localized stress accumulation causes measurable changes in seismic velocity in the Anza region.

Torsional overtone dispersion from correlations of S waves to SS waves

1974 ◽  
Vol 64 (2) ◽  
pp. 313-320
Author(s):  
James N. Brune ◽  
Freeman Gilbert
Keyword(s):  
Travel Time ◽  
Source Region ◽  
Correlation Method ◽  
Phase Correlation ◽  
Earth Model ◽  
Base Line ◽  
S Wave ◽  
Time Data ◽  
S Waves ◽  
Travel Time Data

abstract This paper presents SH overtone dispersion data obtained by using the phase correlation method of Brune (1964). The data augment the set provided by longer-period spheroidal and toroidal mode data and travel-time data. A major advantage of the phase-correlation method over travel-time data is the elimination, to first order, of source effects and source-region bias. The overtone data are consistent with lower-order spheroidal overtone data indicating a base-line correction of 4.0 ± 0.9 sec to the S-wave travel-time data of Hales and Roberts (1970). These and other fundamental-mode and overtone data, travel-time data, and mass and moment of inertia comprise 497 gross earth data and represent one more step in the march toward a spherically averaged earth model.

scholarly journals Body-wave amplitude and travel-time correlations across North America

1983 ◽  
Vol 73 (4) ◽  
pp. 1063-1076
Author(s):  
Thorne Lay ◽  
Donald V. Helmberger
Keyword(s):  
North America ◽  
Travel Time ◽  
Body Wave ◽  
Rocky Mountain ◽  
S Wave ◽  
Arrival Times ◽  
S Waves ◽  
Long Period ◽  
Amplitude Data ◽  
Short Period

abstract Relationships between travel-time and amplitude station anomalies are examined for short- and long-period SH waves and short-period P waves recorded at North American WWSSN and Canadian Seismic Network stations. Data for two azimuths of approach to North America are analyzed. To facilitate intercomparison of the data, the S-wave travel times and amplitudes are measured from the same records, and the amplitude data processing is similar for both P and S waves. Short-period P- and S-wave amplitudes have similar regional variations, being relatively low in the western tectonic region and enhanced in the shield and mid-continental regions. The east coast has intermediate amplitude anomalies and systematic, large azimuthal travel-time variations. There is a general correlation between diminished short-period amplitudes and late S-wave arrival times, and enhanced amplitudes and early arrivals. However, this correlation is not obvious within the eastern and western provinces separately, and the data are consistent with a step-like shift in amplitude level across the Rocky Mountain front. Long-period S waves show no overall correlation between amplitude and travel-time anomalies.

Travel-time curves and upper-mantle structure from long period S waves

1967 ◽  
Vol 57 (5) ◽  
pp. 1063-1092 ◽  
Author(s):  
Abou-Bakr K. Ibrahim ◽  
Otto W. Nuttli
Keyword(s):  
Travel Time ◽  
Upper Mantle ◽  
Earth Model ◽  
S Wave ◽  
Time Data ◽  
Low Velocity ◽  
S Waves ◽  
Long Period ◽  
Travel Time Data ◽  
Proposed Model

abstract Long-period S-wave travel-time data, including second and later arrivals, are presented for distances of 3° to 65° for focal depths of 33 and 120 km. Onset times were determined on the basis of particle motion diagrams and the product of the horizontal radial and vertical components of motion. Because the recording stations principally were LRSM units, the travel times represent data for an “average” United States earth model. An S-wave velocity distribution calculated for the upper mantle provides a satisfactory fit to the empirical travel-time data for focal depths of both 33 and 120 km. The proposed model contains a pronounced low-velocity layer at a depth of about 150-200 km, and secondary low-velocity layers at depths of 340-370 km and of 670-710 km. In addition, there are regions of rapidly increasing velocity beginning at depths of about 400 and 750 km, and constant velocity zones at 220-350 km and 400-670 km.

scholarly journals Array data processing techniques applied to long-period shear waves at Fennoscandian seismograph stations

1969 ◽  
Vol 59 (5) ◽  
pp. 1863-1887
Author(s):  
James H. Whitcomb
Keyword(s):  
Data Processing ◽  
Velocity Ratio ◽  
Underground Explosion ◽  
High Signal ◽  
S Wave ◽  
Array Data ◽  
S Waves ◽  
Long Period ◽  
Normal Record ◽  
The Individual

abstract Array data processing is applied to long-period records of S waves at a network of five Fennoscandian seismograph stations (Uppsala, Umeå, Nurmijärvi, Kongsberg, Copenhagen) with a maximum separation of 1300 km. Records of five earthquakes and one underground explosion are included in the study. The S motion is resolved into SH and SV, and after appropriate time shifts the individual traces are summed, both directly and after weighting. In general, high signal correlation exists among the different stations involved resulting in more accurate time readings, especially for records which have amplitudes that are too small to be read normally. S-wave station residuals correlate with the general crustal type under each station. In addition, the Fennoscandian shield may have a higher SH/SV velocity ratio than the adjacent tectonic area to the northwest.SV-to-P conversion at the base of the crust can seriously interfere with picking the onset of Sin normal record reading. The study demonstrates that, for epicentral distances beyond about 30°, existing networks of seismograph stations can be successfully used for array processing of long-period arrivals, especially the S arrivals.

scholarly journals Travel-Time Inversion Method of Converted Shear Waves Using RayInvr Algorithm

2021 ◽  
Vol 11 (8) ◽  
pp. 3571
Author(s):  
Genggeng Wen ◽  
Kuiyuan Wan ◽  
Shaohong Xia ◽  
Huilong Xu ◽  
Chaoyan Fan ◽  
...  
Keyword(s):  
Travel Time ◽  
Wave Velocity ◽  
P Wave ◽  
Inversion Method ◽  
Time Inversion ◽  
Ocean Bottom Seismometer ◽  
S Wave ◽  
S Waves ◽  
Inversion Model ◽  
Travel Time Inversion

The detailed studies of converted S-waves recorded on the Ocean Bottom Seismometer (OBS) can provide evidence for constraining lithology and geophysical properties. However, the research of converted S-waves remains a weakness, especially the S-waves’ inversion. In this study, we applied a travel-time inversion method of converted S-waves to obtain the crustal S-wave velocity along the profile NS5. The velocities of the crust are determined by the following four aspects: (1) modelling the P-wave velocity, (2) constrained sediments Vp/Vs ratios and S-wave velocity using PPS phases, (3) the correction of PSS phases’ travel-time, and (4) appropriate parameters and initial model are selected for inversion. Our results show that the vs. and Vp/Vs of the crust are 3.0–4.4 km/s and 1.71–1.80, respectively. The inversion model has a similar trend in velocity and Vp/Vs ratios with the forward model, due to a small difference with ∆Vs of 0.1 km/s and ∆Vp/Vs of 0.03 between two models. In addition, the high-resolution inversion model has revealed many details of the crustal structures, including magma conduits, which further supports our method as feasible.

Seismic P- and S-wave velocity Tomography in Scandinavia

2020 ◽  
Author(s):  
Nevra Bulut ◽  
Valerie Maupin ◽  
Hans Thybo
Keyword(s):  
Travel Time ◽  
North Atlantic ◽  
Upper Mantle ◽  
Body Waves ◽  
Significant Heterogeneity ◽  
Finite Frequency ◽  
S Wave ◽  
The North ◽  
The North Atlantic ◽  
High Topography

<p>The causes of the high topography in Scandinavia along the North Atlantic passive continental margins are enigmatic, and two end-member models have been proposed. One opinion is that the high topography has been maintained since the Caledonian orogeny, because isostatic rebound has compensated for most of the erosion over >400 My. The other opinion is that the topography is Cenozoic and that it is related to plate tectonic or deep thermal / geodynamic processes. Onshore uplift is related to simultaneous offshore subsidence, and the rapid topographic changes may be the combined result of a series of complementary processes.</p><p>Here, we provide new evidence for the upper mantle structure by calculating a tomographic model for Fennoscandia (Scandinavia and Finland) by teleseismic inversion of finite-frequency P- and S- wave travel-time residuals. We use seismic signals from earthquakes at epicentral distances between 30° and 104° and with magnitudes larger than 5.5, gathered on 200 broad-band seismic stations installed by the ScanArray project in Norway, Sweden and Finland, which operated during 2012-2017, together with data from earlier projects and stationary stations..</p><p>We measure relative travel-time residuals of direct body waves in high- and low-frequency bands, and carry out an appropriate frequency-dependent crustal correction. The average residuals vary over the region, and show clear trends depending on location and and back-azimuthal directions. This demonstrates the presence of significant heterogeneity of seismic velocities in the upper mantle across the region. Based on the travel-time residuals<strong>,</strong> we carry out finite-frequency body-wave tomographic inversion to determine the P and S wave seismic velocity structure of the upper-mantle. By use of “relative kernels” we reduce problems related to station coverage with asynchronous datasets, which allows the use of data from different deployments for the inversion. The resulting seismic model is compared to the existing and past topography in order to contribute to the understanding of mechanisms responsible for the topographic changes in the Fennoscandian region, which we relate to the general tectonic and geological evolution of the North Atlantic region. The models provide basis for deriving high-resolution models of temperature and compositional anomalies that may contribute to the understanding of the observed, enigmatic topography.</p>

Tomographic imaging of permafrost using three-component seismic cone-penetration test

Geophysics ◽  
2006 ◽  
Vol 71 (5) ◽  
pp. H55-H65 ◽  
Author(s):  
Anne-Marie LeBlanc ◽  
Richard Fortier ◽  
Calin Cosma ◽  
Michel Allard
Keyword(s):  
Tomographic Imaging ◽  
Unfrozen Water ◽  
Seismic Velocities ◽  
S Wave ◽  
Cone Penetration ◽  
Arrival Times ◽  
S Waves ◽  
Seismic Properties ◽  
Unfrozen Water Content ◽  
First Arrival

We conducted seismic cone-penetration tests (SCPT) and tomographic imaging in a permafrost mound in northern Quebec, Canada, to study the cryostratigraphy and assess the seismic properties of permafrost at temperatures near [Formula: see text]. A swept impact source generating both P- and S-waves and penetrometer-mounted three-component accelerometers were used to acquire surface-to-depth first-arrival times as input to produce 2D images of P- and S-wave velocities. Based on the three-component accelerometer records and the propagation modes of body waves, the P- and S-wave first arrivals were detected and discriminated. The inversion of the first-arrival times was based on the simultaneous iterative reconstruction technique. The multioffset surface-to-depth geometry used in this study limits the lateral resolution of tomographic imaging. However, the vertical variation in seismic velocities in the permafrost mound shows good reproducibility and can be compared to the cone data. The gathering of cone data such as cone resistance, friction ratio, electrical resistivity, and temperature, along with the seismic velocities, provides new insights into the cryostratigraphy of permafrost. While the cone data are affected by the vertical heterogeneity because of the complex sequence of ice lenses and frozen soil layers of a few centimeters thickness, the smooth velocity variations of P- and S-waves characterized by a wavelength of a few meters depend on the bulk physical properties of permafrost. The P- and S-wave velocities varied from [Formula: see text] and from [Formula: see text], respectively, for a temperature range between [Formula: see text] and [Formula: see text]. At this temperature range, the variations in unfrozen water content are important and affect directly the seismic properties of permafrost. The decrease in P- and S-waves velocities in depth with the permafrost mound depends nonlinearly on the increase of unfrozen water content from 9% to 30% for a temperature increase from [Formula: see text].

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