scholarly journals A hybrid method to compute short-period synthetic seismograms of teleseismic body waves in a 3-D regional model

2012 ◽  
Vol 192 (1) ◽  
pp. 230-247 ◽  
Author(s):  
Vadim Monteiller ◽  
Sébastien Chevrot ◽  
Dimitri Komatitsch ◽  
Nobuaki Fuji
Keyword(s):  
Hybrid Method ◽  
Regional Model ◽  
Synthetic Seismograms ◽  
Body Waves ◽  
Short Period

scholarly journals On the validity of the planar wave approximation to compute synthetic seismograms of teleseismic body waves in a 3-D regional model

2020 ◽  
Vol 224 (3) ◽  
pp. 2060-2076
Author(s):  
Vadim Monteiller ◽  
Stephen Beller ◽  
Bastien Plazolles ◽  
Sébastien Chevrot
Keyword(s):  
Epicentral Distance ◽  
Spectral Element ◽  
Synthetic Seismograms ◽  
Body Waves ◽  
Earth Model ◽  
Secondary Phases ◽  
P Waves ◽  
Short Period ◽  
Wide Range ◽  
Injection Methods

SUMMARY Injection methods are a very efficient means to compute synthetic seismograms of short-period teleseismic body waves in 3-D regional models. The principle is to inject an incident teleseismic wavefield inside a regional 3-D Cartesian spectral-element grid. We have developed an opern-source package that allows us to inject either an incident plane wave, computed with a frequency–wavenumber method, or the complete wavefield, computed in a spherically symmetric reference earth model with AxiSEM. The computations inside the regional spectral-element grid are performed with SPECFEM3D_Cartesian. We compare the efficiency and reliability of the two injection methods for teleseismic P waves, considering a wide range of epicentral distance and hypocentral depths. Our simulations demonstrate that in practice the effects of wave front and Earth curvature are negligible for moderate size regional domains (several hundreds of kilometres) and for periods larger than 2 s. The main differences observed in synthetic seismograms are related to secondary phases that have a different slowness from the one of the reference P phase.

The foreshock sequence of the 1986 Chalfant, California, earthquake

1988 ◽  
Vol 78 (1) ◽  
pp. 172-187
Author(s):  
Kenneth D. Smith ◽  
Keith F. Priestley
Keyword(s):  
Main Shock ◽  
Slip Surface ◽  
Body Waves ◽  
Aftershock Distribution ◽  
Time Period ◽  
Main Shocks ◽  
Short Period ◽  
Local Shear ◽  
Stress Drops ◽  
Foreshock Activity

Abstract The ML 6.4 Chalfant, California, earthquake of 21 July 1986 was preceded by an extensive foreshock sequence. Foreshock activity is characterized by shallow clustering activity, including 7 events greater than ML 3, beginning 18 days before the earthquake, an ML 5.7 foreshock 24 hr before the main shock that ruptured only in the upper 10 km of the crust, and an “off-fault” cluster of activity perpendicular to the slip surface of the ML 5.7 foreshock associated with the hypocenter of the main shock. The Chalfant sequence occurred within the local short-period network, and the spatial and temporal development of the foreshock sequence can be observed in detail. Seismicity of the July 1986 time period is largely confined to two nearly conjugate planes; one striking N30°E and dipping 60° to the northwest associated with the ML 5.7 foreshock and the other striking N25°W and dipping 70° to the southwest associated with the main shock. Focal mechanisms for the foreshock period fall into two classes in agreement with these two planes. Shallow clustering of earthquakes in July and the ML 5.7 principal foreshock occur at the intersection of the two planes at a depth of approximately 7 km. The seismic moments determined from inversion of the teleseismic body waves are 4.2 × 1025 and 2.5 × 1025 dyne-cm for the principal foreshock and the main shock, respectively. Slip areas for these two events can be estimated from the aftershock distribution and result in stress drops of 63 bars for the principal foreshock and 16 bars for the main shock. The main shock occurred within an “off-fault” cluster of earthquakes associated with the principal foreshock. This cluster of activity occurs at a predicted local shear stress high in relation to the slip surface of the 20 July earthquake, and this appears to be the triggering mechanism of the main shock. The shallow rupture depth of the principal foreshock indicates that this event was anomalous with respect to the character of main shocks in the region.

Short-period seismic noise

1967 ◽  
Vol 57 (1) ◽  
pp. 55-81
Author(s):  
E. J. Douze
Keyword(s):  
Surface Waves ◽  
Rayleigh Waves ◽  
Seismic Noise ◽  
Body Waves ◽  
Deep Hole ◽  
Period Range ◽  
Short Period ◽  
The Subject ◽  
Hole Arrays

abstract This report consists of a summary of the studies conducted on the subject of short-period (6.0-0.3 sec period) noise over a period of approximately three years. Information from deep-hole and surface arrays was used in an attempt to determine the types of waves of which the noise is composed. The theoretical behavior of higher-mode Rayleigh waves and of body waves as measured by surface and deep-hole arrays is described. Both surface and body waves are shown to exist in the noise. Surface waves generally predominate at the longer periods (of the period range discussed) while body waves appear at the shorter periods at quiet sites. Not all the data could be interpreted to define the wave types present.

Upper-mantle discontinuity from amplitude data of P′P′ and its precursors

1973 ◽  
Vol 63 (2) ◽  
pp. 587-597
Author(s):  
Ta-Liang Teng ◽  
James P. Tung
Keyword(s):  
Upper Mantle ◽  
Body Waves ◽  
P Wave ◽  
Specific Reference ◽  
Amplitude Data ◽  
Surface Displacements ◽  
Short Period ◽  
Mantle Velocity ◽  
Mantle Discontinuity ◽  
Upper Mantle Discontinuity

abstract Recent observations of P′P′ and its precursors, identified as reflections from within the Earth's upper mantle, are used to examine the structure of the uppermantle discontinuities with specific reference to the density, the S velocity, and the Q variations. The Haskell-Thomson matrix method is used to generate the complex reflection spectrum, which is then Fourier synthesized for a variety of upper-mantle velocity-density and Q models. Surface displacements are obtained for the appropriate recording instrument, permitting a direct comparison with the actual seismograms. If the identifications of the P′P′ precursors are correct, our proposed method yields the following: (1) a structure of Gutenberg-Bullen A type is not likely to produce observable P′P′ upper-mantle reflections, (2) in order that a P′P′ upper-mantle reflection is strong enough to be observed, first-order density and S-velocity discontinuities together with a P-wave discontinuity are needed at a depth of about 650 km, and (3) corresponding to a given uppermantle velocity-density model, an estimate can be made of the Q in the upper mantle for short-period seismic body waves.

Imaging the Ice Sheet and Uppermost Crustal Structures with a Dense Linear Seismic Array in the Larsemann Hills, Prydz Bay, East Antarctica

2021 ◽  
Author(s):  
Lei Fu ◽  
Jingxue Guo ◽  
Junlun Li ◽  
Bao Deng ◽  
Guofeng Liu ◽  
...  
Keyword(s):  
High Resolution ◽  
Ice Sheet ◽  
Velocity Model ◽  
Dispersion Curves ◽  
Body Waves ◽  
East Antarctica ◽  
Prydz Bay ◽  
Larsemann Hills ◽  
Geophysical Surveys ◽  
Short Period

Abstract Comprehensive geophysical surveys including magnetotelluric, seismic, and aerial gravity–magnetic surveys are essential for understanding the history of Antarctic tectonics. The ice sheet and uppermost structure derived from those geophysical methods are relatively low resolution. Although ice-penetrating radar can provide high-resolution reflectivity images of the ice sheet, it cannot provide constraints on subice physical properties, which are important for geological understanding of the Antarctic continent. To obtain high-resolution images of the ice sheet and uppermost crustal structure beneath the Larsemann Hills, Prydz Bay, East Antarctica, we conduct an ambient noise seismic experiment with 100 short-period seismometers spaced at 0.2 km intervals. Continuous seismic waveforms are recorded for one month at a 2 ms sampling rate. Empirical Green’s functions are extracted by cross correlating the seismic waveform of one station with that of another station, and dispersion curves are extracted using a new phase-shift method. A high-resolution shear-velocity model is derived by inverting the dispersion curves. Furthermore, body waves are enhanced using a set of processing techniques commonly used in seismic exploration. The stacked body-wave image clearly shows a geological structure similar to that revealed by the shear-wave velocity model. This study, which is the first of its kind in Antarctica, possibly reveals a near-vertical intrusive rock covered by an ice sheet with a horizontal extent of 4 km. Our results help to improve the understanding of the subice environment and geological evolution in the Larsemann Hills, Prydz Bay, East Antarctica.

A hybrid method to calculate teleseismic body waves in a regional 3D model using GEMINI and SPECFEM.

2021 ◽  
Author(s):  
Thomas Möller ◽  
Wolfgang Friederich
Keyword(s):  
Wave Propagation ◽  
Hybrid Method ◽  
Velocity Model ◽  
Absorbing Boundary Conditions ◽  
Body Waves ◽  
P Wave ◽  
Spherically Symmetric ◽  
Target Region ◽  
3D Simulations ◽  
Earth Models

<p>Modeling waveforms of teleseismic body waves requires the solution of the seismic wave equation in the entire Earth. Since fully-numerical 3D simulations on a global scale with periods of a few seconds are far too computationally expensive, we resort to a hybrid approach in which fully-numerical 3D simulations are performed only within the target region and wave propagation through the rest of the Earth is modeled using methods that are much faster but apply only to spherically symmetric Earth models.</p><p>We present a hybrid method that uses GEMINI to compute wave fields for a spherically symmetric Earth model up to the boundaries of a regional box. The wavefield is injected at the boundaries, where wave propagation is continued using SPECFEM-Cartesian. Inside the box, local heterogeneities in the velocity distribution are allowed, which can cause scattered and reflected waves. To prevent these waves from reflecting off the edges of the box absorbing boundary conditions are specifically applied to these parts of the wavefields. They are identified as the difference between the wavefield calculated with SPECFEM at the edges and the incident wavefield.</p><p>The hybrid method is applied to a target region in and around the Alps as a test case. The region covers an area of 1800 by 1350 km centered at 46.2°N and 10.87°E and includes crust and mantle to a depth of 600 km. We compare seismograms with a period of up to ten seconds calculated with the hybrid method to those calculated using GEMINI only for identical 1D earth models. The comparison of the seismograms shows only very small differences and thus validates the hybrid method. In addition, we demonstrate the potential of the method by calculating seismograms where the 1D velocity model inside the box is replaced by a velocity model generated using P-wave traveltime tomography.</p>

Attenuation of short-period body waves in Northwestern Himalayan Region, India

2018 ◽  
Vol 114 ◽  
pp. 555-562
Author(s):  
Priyamvada Singh ◽  
Sushil Kumar ◽  
Pitam Singh
Keyword(s):  
Body Waves ◽  
Himalayan Region ◽  
Short Period
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