scholarly journals Improvements of the shock arrival times at the Earth model STOA

2015 ◽  
Vol 120 (7) ◽  
pp. 5290-5297 ◽  
Author(s):  
H.-L. Liu ◽  
G. Qin
Keyword(s):  
Earth Model ◽  
Arrival Times ◽  
The Earth

INVESTIGATING S VELOCITY STRUCTURE OF THE UPPER MANTLE BENEATH WEST INDONESIA USING SEISMOGRAM ANALYSIS OF TWO STRONG SOUTH JAVA EARTHQUAKES IN MALAYSIAN SEISMOLOGICAL NETWORK

2010 ◽  
Vol 04 (04) ◽  
pp. 321-339
Author(s):  
BAGUS JAYA SANTOSA
Keyword(s):  
Upper Mantle ◽  
Velocity Structure ◽  
Corner Frequency ◽  
Earth Model ◽  
Time Data ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Arrival Times ◽  
The Earth ◽  
Seismological Network

This research investigated the S speed structure in the upper mantle beneath West Indonesia by analyzing the seismogram triggered by the C052606A and C071706B earthquakes in South Java and recorded at the Malaysian seismological network MY. The method used is waveform comparison between the measured seismogram and the synthetic one in the time domain and three Cartesian components simultaneously, instead of travel time data or dispersion curve, which are commonly used by other seismologists. The seismogram comparison was conducted in the same unit and a low-pass filter with 20 mHz corner frequency was applied to both seismograms. Seismogram analysis shows very strong deviations in the arrival times and amplitudes of the Love and Rayleigh surface waveforms. To solve the observed deviation, a correction on the earth structure covering the speed gradient of βh and the value of zero-order coefficients for the βh and βv in the earth upper mantle is required. The research's result shows that the area of East Sumatra and Borneo has negative correction of S speed structure in the upper mantle layers, compared to PREMAN standard earth model. This result is different from other seismological result.

Seismic Rays

2017 ◽  
Author(s):  
John A. Adam
Keyword(s):  
Inverse Problem ◽  
Seismic Tomography ◽  
Seismic Waves ◽  
Seismic Station ◽  
Three Dimensional ◽  
Arrival Times ◽  
The Earth ◽  
Straight Lines ◽  
Ray Path ◽  
Uniform Composition

This chapter focuses on the underlying mathematics of seismic rays. Seismic waves caused by earthquakes and explosions are used in seismic tomography to create computer-generated, three-dimensional images of Earth's interior. If the Earth had a uniform composition and density, seismic rays would travel in straight lines. However, it is broadly layered, causing seismic rays to be refracted and reflected across boundaries. In order to calculate the speed along the wave's ray path, the time it takes for a seismic wave to arrive at a seismic station from an earthquake needs to be determined. Arrival times of different seismic waves allow scientists to define slower or faster regions deep in the Earth. The chapter first presents the relevant equations for seismic rays before discussing how rays are propagated in a spherical Earth. The Wiechert-Herglotz inverse problem is considered, along with the properties of X in a horizontally stratified Earth.

2.1.3.2 The earth model

2005 ◽  
pp. 85-96
Author(s):  
A. M. Dziewonski ◽  
D. L. Anderson
Keyword(s):  
Earth Model ◽  
The Earth

scholarly journals Rigid-Earth Nutation Models

2000 ◽  
Vol 180 ◽  
pp. 190-195
Author(s):  
J. Souchay
Keyword(s):  
Transfer Function ◽  
Rigid Body ◽  
Earth Model ◽  
High Quality ◽  
Frequency Dependent ◽  
Relative Improvement ◽  
The Earth ◽  
Rigid Earth

AbstractDespite the fact that the main causes of the differences between the observed Earth nutation and that derived from analytical calculations come from geophysical effects associated with nonrigidity (core flattening, core-mantle interactions, oceans, etc…), efforts have been made recently to compute the nutation of the Earth when it is considered to be a rigid body, giving birth to several “rigid Earth nutation models.” The reason for these efforts is that any coefficient of nutation for a realistic Earth (including effects due to nonrigidity) is calculated starting from a coefficient for a rigid-Earth model, using a frequency-dependent transfer function. Therefore it is important to achieve high quality in the determination of rigid-Earth nutation coefficients, in order to isolate the nonrigid effects still not well-modeled.After reviewing various rigid-Earth nutation models which have been established recently and their relative improvement with respect to older ones, we discuss their specifics and their degree of agreement.

Validity of Resolving the 785 km Discontinuity in the Lower Mantle with P′P′ Precursors?

2020 ◽  
Vol 91 (6) ◽  
pp. 3278-3285
Author(s):  
Baolong Zhang ◽  
Xiangfang Zeng ◽  
Jun Xie ◽  
Vernon F. Cormier
Keyword(s):  
Lower Mantle ◽  
Forward Modeling ◽  
Earth Model ◽  
Frequency Content ◽  
Waveform Data ◽  
Mantle Discontinuities ◽  
The Earth ◽  
Earth Models ◽  
Beamforming Technique ◽  
Ray Paths

Abstract P ′ P ′ precursors have been used to detect discontinuities in the lower mantle of the Earth, but some seismic phases propagating along asymmetric ray paths or scattered waves could be misinterpreted as reflections from mantle discontinuities. By forward modeling in standard 1D Earth models, we demonstrate that the frequency content, slowness, and decay with distance of precursors about 180 s before P′P′ arrival are consistent with those of the PKPPdiff phase (or PdiffPKP) at epicentral distances around 78° rather than a reflection from a lower mantle interface. Furthermore, a beamforming technique applied to waveform data recorded at the USArray demonstrates that PKPPdiff can be commonly observed from numerous earthquakes. Hence, a reference 1D Earth model without lower mantle discontinuities can explain many of the observed P′P′ precursors signals if they are interpreted as PKPPdiff, instead of P′785P′. However, this study does not exclude the possibility of 785 km interface beneath the Africa. If this interface indeed exists, P′P′ precursors at distances around 78° would better not be used for its detection to avoid interference from PKPPdiff. Indeed, it could be detected with P′P′ precursors at epicentral distances less than 76° or with other seismic phases such as backscattered PKP·PKP waves.

scholarly journals New measurements of long-period radial modes using large earthquakes

2020 ◽  
Vol 224 (2) ◽  
pp. 1211-1224
Author(s):  
S Talavera-Soza ◽  
A Deuss
Keyword(s):  
Inner Core ◽  
Cross Coupling ◽  
Earth Model ◽  
Cylindrical Anisotropy ◽  
Long Period ◽  
Centre Frequency ◽  
The Earth ◽  
Radial Anisotropy ◽  
Crucial Information ◽  
Quality Factor Q

SUMMARY Radial modes, nS0, are long-period oscillations that describe the radial expansion and contraction of the whole Earth. They are characterized only by their centre frequency and quality factor Q, and provide crucial information about the 1-D structure of the Earth. Radial modes were last measured more than a decade ago using only one or two earthquakes. Here, we measure radial modes using 16 of the strongest and deepest earthquakes of the last two decades. By introducing more earthquake data into our measurements, we improve our knowledge of 1-D attenuation, as we remove potential earthquake bias from our results. For mode 0S0, which is dominated by compressional energy, we measure a Q value of 5982, much higher than previously measured, and requiring less bulk attenuation in the Earth than previously thought. We also show that radial modes cross-couple (resonate) strongly to their nearest spheroidal mode due to ellipticity and inner core cylindrical anisotropy. Cross-coupling improves the fit between data and synthetics, and gives better estimates of the centre frequency and attenuation value of the radial modes. Including cross-coupling in our measurements results in a systematic shift of the centre frequencies of radial modes towards the Preliminary Reference Earth Model. This shift in centre frequencies, has implications for the strength of the radial anisotropy present in the uppermost inner core, with our cross-coupling results agreeing with lower values of anisotropy than the ones inferred from just measuring the modes in self-coupling (isolation). Furthermore, cross-coupling between radial modes and angular-order two modes provides constraints on cylindrical inner core anisotropy, that will help us improve our knowledge of the 3-D structure of the inner core.

Integrated use of the Earth model in subsalt seismic prestack imaging

1998 ◽  
Author(s):  
Joe Stefani ◽  
Bob Shank ◽  
David C. Bartel ◽  
William L. Abriel
Keyword(s):  
Earth Model ◽  
The Earth

The Research into the Visual and Simulated System of the Orbiting Satellite

2013 ◽  
Vol 753-755 ◽  
pp. 1324-1327
Author(s):  
Jia Qiang Dong
Keyword(s):  
Real Time ◽  
Time Management ◽  
Simulation System ◽  
Earth Model ◽  
Virtual Training ◽  
The Real ◽  
Whole Process ◽  
Network Training ◽  
The Earth ◽  
Simulated System

The visual and simulated system of the orbiting satellite based on the OpenGL technology is designed and realized in this paper, in which a visualization platform of the satellite in-orbit running is constructed. The simulation system has constructed the satellite model and the earth model by making use of 3DS MAX technology, and achieved the visualization of satellite in-orbit-running, the visualization of the communication route and of the overlay effect. At the same time, which has realized the access to the database of the orbiting satellite by means of ADO technology .The practices have proven that the system can simulate the whole process of satellite in-orbit-running in real-time, and provides the assistant support platform of the real-time management and decision. Apart from this, the system provides the network training of the space forces with virtual training platform. It is of great significance to construct the virtual battlefield simulation system.

The Earth’s Free Spherical Oscillations of the Great Japan Earthquake

2012 ◽  
Vol 622-623 ◽  
pp. 1664-1669 ◽  
Author(s):  
Ye Wu ◽  
Yong Ge Wan ◽  
Liang Ding
Keyword(s):  
Free Oscillation ◽  
Low Frequency ◽  
Earth Model ◽  
Frequency Signal ◽  
The Earth ◽  
Oscillation Modes ◽  
Spectral Splitting ◽  
Earth’S Free Oscillations ◽  
Earth’S Free Oscillation ◽  
Digital Seismic Network

An M9.0 earthquake struck Japan on March 11, 2011 and the strong earthquake made continuous oscillation of the Earth. We first studied the Earth’s free oscillations using observations of VHZ channel of China Digital Seismic Network (CDSN). Since the frequency response of seismograph in CDSN suppresses the information of low frequency signal, we do not need to remove the solid tide in our data processing. We extracted 72 clear spherical modes of (0S0,0S2to0S72) of the Earth’s free oscillation and 21 harmonic modes and they are consistent and nearly same with the frequencies of the modes of Preliminary Reference Earth Model (PREM). Spectral splitting phenomenon is observed obviously in0S2,0S3,0S4and1S2free oscillation modes.

Wavelet estimation for a multidimensional acoustic or elastic earth

Geophysics ◽  
1990 ◽  
Vol 55 (7) ◽  
pp. 902-913 ◽  
Author(s):  
Arthur B. Weglein ◽  
Bruce G. Secrest
Keyword(s):  
Estimation Method ◽  
Normal Derivative ◽  
Source Spectrum ◽  
Earth Model ◽  
Far Field ◽  
Wavelet Estimation ◽  
Seismic Wavelet ◽  
Array Pattern ◽  
The Earth ◽  
Source Array

A new and general wave theoretical wavelet estimation method is derived. Knowing the seismic wavelet is important both for processing seismic data and for modeling the seismic response. To obtain the wavelet, both statistical (e.g., Wiener‐Levinson) and deterministic (matching surface seismic to well‐log data) methods are generally used. In the marine case, a far‐field signature is often obtained with a deep‐towed hydrophone. The statistical methods do not allow obtaining the phase of the wavelet, whereas the deterministic method obviously requires data from a well. The deep‐towed hydrophone requires that the water be deep enough for the hydrophone to be in the far field and in addition that the reflections from the water bottom and structure do not corrupt the measured wavelet. None of the methods address the source array pattern, which is important for amplitude‐versus‐offset (AVO) studies. This paper presents a method of calculating the total wavelet, including the phase and source‐array pattern. When the source locations are specified, the method predicts the source spectrum. When the source is completely unknown (discrete and/or continuously distributed) the method predicts the wavefield due to this source. The method is in principle exact and yet no information about the properties of the earth is required. In addition, the theory allows either an acoustic wavelet (marine) or an elastic wavelet (land), so the wavelet is consistent with the earth model to be used in processing the data. To accomplish this, the method requires a new data collection procedure. It requires that the field and its normal derivative be measured on a surface. The procedure allows the multidimensional earth properties to be arbitrary and acts like a filter to eliminate the scattered energy from the wavelet calculation. The elastic wavelet estimation theory applied in this method may allow a true land wavelet to be obtained. Along with the derivation of the procedure, we present analytic and synthetic examples.

Sign in / Sign up

Export Citation Format

Share Document