Changes in soil conditions before and after earthquakes at a repetitive soil liquefaction site in Taiwan

Geophysics ◽  
2022 ◽  
pp. 1-49
Author(s):  
Yu-Tai Wu
Keyword(s):  
Shear Modulus ◽  
Wave Velocity ◽  
Shear Velocity ◽  
Soil Condition ◽  
Soil Liquefaction ◽  
Soil Conditions ◽  
S Wave ◽  
Liquefaction Potential ◽  
Wave Velocities ◽  
Low Shear

Beishih Village of Hsinhua Township in southern Taiwan is a unique location for studying soil liquefaction. Soil liquefaction was observed at the same site after earthquakes in 1946, 2010, and 2016, each of which had a Richter magnitude greater than six. This recurrence provides an opportunity for analyzing soil condition variations resulting from soil liquefaction. Seismic data sets were collected in 2011, 2014, 2016, and 2017. We used seismic refraction tomography and the multichannel analysis of surface waves to estimate P- and S-wave velocities. In S-wave velocity profiles, low shear velocity zones were located beneath sand volcanoes shortly after two earthquakes and disappeared 4 years after a 2010 earthquake. However, the P-wave velocity is less sensitive to soil condition changes, possibly because groundwater obscures the effect of soil liquefaction on velocity profiles. In addition, we used seismic wave velocities to determine the importance of soil properties such as Poisson’s ratio, shear modulus, and porosity to identify the cause of the low shear velocity zone. Notably, although porosity decreased after soil grain rearrangement, sand and clay mixing increased the Poisson’s ratio, reducing the shear modulus of the soil. In addition, a soil layer between 2 and 7 m and a deeper layer below 10 m that resulted in sand volcanoes were both liquefied. We also considered how the evaluation of soil liquefaction potential could be affected by long-term variations in soil conditions and changes resulting from liquefaction. The factor of safety was used to evaluate the liquefaction potential of the site. The results revealed that the assessment conducted long after the earthquake underestimated risk because the soil developed shear strength after the earthquake.

Impact of change in pore-fill material on P-wave velocity

Geophysics ◽  
2014 ◽  
Vol 79 (6) ◽  
pp. D399-D407 ◽  
Author(s):  
Nishank Saxena ◽  
Gary Mavko
Keyword(s):  
Shear Modulus ◽  
Wave Velocity ◽  
P Wave ◽  
Exact Equation ◽  
Fluid Substitution ◽  
Seismic Velocities ◽  
S Wave ◽  
Wave Velocities ◽  
Fill Material ◽  
P Wave Velocity

The problem of predicting the change in seismic velocities (P-wave and S-wave) upon the change in pore-fill material properties is commonly known as substitution. For isotropic rocks, P- and S-wave velocities are fundamentally linked to the effective P-wave and shear moduli. The change in the S-wave velocity or shear modulus upon fluid substitution can be predicted with Gassmann’s equations starting only with the initial S-wave velocity. However, predicting changes in P-wave velocity or the P-wave modulus requires knowledge of the initial P- and S-wave velocities. We initiated a rigorous derivation of the P-wave modulus for fluid and solid substitution in monomineralic isotropic rocks for cases in which an estimate of the S-wave velocity or shear modulus is not available. For the general case of solid substitution, the exact equation for the P-wave modulus depends on parameters that are usually unknown. However, for fluid substitution, fewer parameters are required. As Poisson’s ratio increases for the mineral in the rock frame, the dependence of exact substitution on these unknown parameters decreases. As a result, in the absence of shear velocity, P-wave modulus fluid substitution can, for example, be performed with higher confidence for rocks with a calcite or dolomite frame than it can for rocks with quartz frame. We evaluated a recipe for applying the new P-wave modulus fluid substitution. This improves on existing work and is recommended for practice.

scholarly journals Subsonic near-surface P-velocity and low S-velocity observations using propagator inversion

Geophysics ◽  
2005 ◽  
Vol 70 (4) ◽  
pp. R15-R23 ◽  
Author(s):  
Robbert van Vossen ◽  
Andrew Curtis ◽  
Jeannot Trampert
Keyword(s):  
Shear Velocity ◽  
Confining Pressure ◽  
Compressional Wave ◽  
P Wave ◽  
Soil Conditions ◽  
Detailed Knowledge ◽  
S Wave ◽  
Near Surface ◽  
Unconsolidated Sands ◽  
Wave Velocities

Detailed knowledge of near-surface P- and S-wave velocities is important for processing and interpreting multicomponent land seismic data because (1) the entire wavefield passes through and is influenced by the near-surface soil conditions, (2) both source repeatability and receiver coupling also depend on these conditions, and (3) near-surface P- and S-wave velocities are required for wavefield decomposition and demultiple methods. However, it is often difficult to measure these velocities with conventional techniques because sensitivity to shallow-wave velocities is low and because of the presence of sharp velocity contrasts or gradients close to the earth's free surface. We demonstrate that these near-surface P- and S-wave velocities can be obtained using a propagator inversion. This approach requires data recorded by at least one multicomponent geophone at the surface and an additional multicomponent geophone at depth. The propagator between them then contains all information on the medium parameters governing wave propagation between the geophones at the surface and at depth. Hence, inverting the propagator gives local estimates for these parameters. This technique has been applied to data acquired in Zeist, the Netherlands. The near-surface sediments at this site are unconsolidated sands with a thin vegetation soil on top, and the sediments considered are located above the groundwater table. A buried geophone was positioned 1.05 m beneath receivers on the surface. Propagator inversion yielded low near-surface velocities, namely, 270 ± 15 m/s for the compressional-wave velocity, which is well below the sound velocity in air, and 150 ± 9 m/s for the shear velocity. Existing methods designed for imaging deeper structures cannot resolve these shallow material properties. Furthermore, velocities usually increase rapidly with depth close to the earth's surface because of increasing confining pressure. We suspect that for this reason, subsonic near-surface P-wave velocities are not commonly observed.

The relation between seismic P‐ and S‐wave velocity dispersion in saturated rocks

Geophysics ◽  
1994 ◽  
Vol 59 (1) ◽  
pp. 87-92 ◽  
Author(s):  
Gary Mavko ◽  
Diane Jizba
Keyword(s):  
Wave Velocity ◽  
Large Scale ◽  
Velocity Dispersion ◽  
Seismic Velocity ◽  
Ultrasonic Velocities ◽  
S Wave ◽  
Local Flow ◽  
Wave Velocities ◽  
Shear Compliance

Seismic velocity dispersionin fluid-saturated rocks appears to be dominated by tow mecahnisms: the large scale mechanism modeled by Biot, and the local flow or squirt mecahnism. The tow mechanisms can be distuinguished by the ratio of P-to S-wave dispersions, or more conbeniently, by the ratio of dynamic bulk to shear compliance dispersions derived from the wave velocities. Our formulation suggests that when local flow denominates, the dispersion of the shear compliance will be approximately 4/15 the dispersion of the compressibility. When the Biot mechanism dominates, the constant of proportionality is much smaller. Our examination of ultrasonic velocities from 40 sandstones and granites shows that most, but not all, of the samples were dominated by local flow dispersion, particularly at effective pressures below 40 MPa.

Soil Liquefaction Evaluation of Offshore Site Based on In Situ Shear Wave Velocity Measurements

2013 ◽  
Vol 405-408 ◽  
pp. 470-473
Author(s):  
Sheng Jie Di ◽  
Ming Yuan Wang ◽  
Zhi Gang Shan ◽  
Hai Bo Jia
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Wind Farm ◽  
Soil Liquefaction ◽  
Offshore Wind ◽  
Velocity Measurements ◽  
Liquefaction Resistance ◽  
Liquefaction Potential

A procedure for evaluating liquefaction resistance of soils based on the shear wave velocity measurements is outlined in the paper. The procedure follows the general formal of the Seed-Idriss simplified procedure. In addition, it was developed following suggestions from industry, researchers, and practitioners. The procedure correctly predicts moderate to high liquefaction potential for over 95% of the liquefaction case histories. The case study for the site of offshore wind farm in Jiangsu province is provided to illustrate the application of the proposed procedure. The feature of the soils and the shear wave velocity in-situ tested in site are discussed and the liquefaction potential of the layer is evaluated. The application shows that the layers of the non-cohesive soils in the depths 3-11m may be liquefiable according to the procedure.

scholarly journals Rapid lateral variation of P-wave velocity at the base of the mantle near the edge of the Large-Low Shear Velocity Province beneath the western Pacific

2014 ◽  
Vol 200 (2) ◽  
pp. 1052-1065 ◽  
Author(s):  
Satoru Tanaka ◽  
Hitoshi Kawakatsu ◽  
Masayuki Obayashi ◽  
Y. John Chen ◽  
Jieyuan Ning ◽  
...  
Keyword(s):  
Wave Velocity ◽  
Shear Velocity ◽  
Western Pacific ◽  
P Wave ◽  
Lateral Variation ◽  
P Wave Velocity ◽  
The Western Pacific ◽  
Low Shear

Wavefield simulation and data-acquisition-scheme analysis for LWD acoustic tools in very slow formations

Geophysics ◽  
2011 ◽  
Vol 76 (3) ◽  
pp. E59-E68 ◽  
Author(s):  
Hua Wang ◽  
Guo Tao
Keyword(s):  
Wave Velocity ◽  
Cutoff Frequency ◽  
P Wave ◽  
Flexural Wave ◽  
S Wave ◽  
Low Frequencies ◽  
Wave Velocities ◽  
Dipole System ◽  
P Wave Velocity ◽  
Wavefield Simulation

Propagating wavefields from monopole, dipole, and quadrupole acoustic logging-while-drilling (LWD) tools in very slow formations have been studied using the discrete wavenumber integration method. These studies examine the responses of monopole and dipole systems at different source frequencies in a very slow surrounding formation, and the responses of a quadrupole system operating at a low source frequency in a slow formation with different S-wave velocities. Analyses are conducted of coherence-velocity/slowness relationships (semblance spectra) in the time domain and of the dispersion characteristics of these waveform signals from acoustic LWD array receivers. These analyses demonstrate that, if the acoustic LWD tool is centralized properly and is operating at low frequencies (below 3 kHz), a monopole system can measure P-wave velocity by means of a “leaky” P-wave for very slow formations. Also, for very slow formations a dipole system can measure the P-wave velocity via a leaky P-wave and can measure the S-wave velocity from a formation flexural wave. With a quadrupole system, however, the lower frequency limit (cutoff frequency) of the drill-collar interference wave would decrease to 5 kHz and might no longer be neglected if the surrounding formation becomes a very slow formation, with S-wave velocities at approximately 500 m/s.

Sequential Measurement of Compressional and Shear Velocities of Rock Samples Under Triaxial Pressure

1969 ◽  
Vol 9 (04) ◽  
pp. 378-394 ◽  
Author(s):  
K.P. Desai ◽  
D.P. Helander
Keyword(s):  
Acoustic Wave ◽  
Resonant Frequency ◽  
Wave Velocity ◽  
Resonance Method ◽  
Shear Velocity ◽  
Berea Sandstone ◽  
Rock Samples ◽  
Wave Velocities ◽  
Compressional Velocity ◽  
Wave Properties

Abstract A laboratory measuring system was designed that can precisely and sequential measure both compressional and shear velocities of rock samples under identical conditions of stress distribution and stress history. This is required if accurate and realistic dynamic elastic properties of rocks are to be determined. The hysteresis effect on velocity pressure characteristics of rock was determined to pressure characteristics of rock was determined to illustrate this point. Lead titanate zirconate transducers were used for measuring compressional wave velocity, and AC-cut quartz transducers were used for measuring shear wave velocity. The system was tested using samples of standard material such as aluminum, steel, brass and lucite. Measurements obtained were accurate within 1 percent. percent. Compressional and shear velocities were measured sequentially on 10 samples of Berea sandstone and two samples of Bartlesville sandstone. It was found that 1. Both compressional and shear velocities increased with an increase in applied external pressure. pressure. 2. Compressional velocity depends upon both external (Pe) and internal (Pi) pressure. 3. Shear velocity depends only upon the differential pressure (Pne-Pe-Pi). 4. The nature of the fluid saturant had little effect on compressional velocity. 5. Shear velocity decreased with an increase in the density of the saturant. 6. The Berea sandstone indicated very little anisotropy. 7. The Bartlesville sandstone showed definite anisotropy. Introduction The various properties of an acoustic wave trainvelocity, amplitude, frequency, etc. may be modified, sometimes quite severely by the media through which the wave has traveled. This suggests the use of wave properties to determine, at least in part, the nature of the material through which the part, the nature of the material through which the wave has passed. To accomplish this successfully requires a reliable technique to for obtaining accurate values of all acoustic wave properties. One purpose of this paper is to describe a recently developed system that can precisely and sequentially record acoustic compressional and shear energies as functions both of time and of frequency. One example of the utility of this system is the accurate measurement of compressional and shear velocities through rock samples subjected to triaxial, i.e., simultaneous but independent vertical, circumferential and pore pressure. Since acoustic velocity and elasticity are closely interrelated, such a system would help to determine realistically the elastic properties of rock samples in the laboratory. METHODS FOR THE INDEPENDENT MEASUREMENT OF COMPRESSIONAL AND SHEAR WAVE VELOCITIES Currently there are two suitable nondestructive laboratory techniques for measuring wave velocity through a rock sample under pressure. One is by the resonance method and the other is by the pulse technique. In the resonance method a sample, in the form of a thin wire, rod, or plate, is make to vibrate in the longitudinal, torsional or flexural mode. Resonant frequency is determined by recording the amplitude of vibration as a function of applied frequency; the amplitude is maximum at resonant frequency. For isotropic materials the relationships between resonance frequencies, elastic moduli and acoustic wave velocities are well known. SPEJ p. 378

Acoustic measurements in unconsolidated sands at low effective pressure and overpressure detection

Geophysics ◽  
2002 ◽  
Vol 67 (2) ◽  
pp. 405-412 ◽  
Author(s):  
Manika Prasad
Keyword(s):  
Wave Velocity ◽  
P Wave ◽  
Acoustic Measurements ◽  
S Wave ◽  
Deepwater Drilling ◽  
Unconsolidated Sands ◽  
Wave Velocities ◽  
P Wave Velocity ◽  
Shallow Water Flows ◽  
Low Pressures

Shallow water flows and over‐pressured zones are a major hazard in deepwater drilling projects. Their detection prior to drilling would save millions of dollars in lost drilling costs. I have investigated the sensitivity of seismic methods for this purpose. Using P‐wave information alone can be ambiguous, because a drop in P‐wave velocity (Vp) can be caused both by overpressure and by presence of gas. The ratio of P‐wave velocity to S‐wave velocity (Vp/Vs), which increases with overpressure and decreases with gas saturation, can help differentiate between the two cases. Since P‐wave velocity in a suspension is slightly below that of the suspending fluid and Vs=0, Vp/Vs and Poisson's ratio must increase exponentially as a load‐bearing sediment approaches a state of suspension. On the other hand, presence of gas will also decrease Vp but Vs will remain unaffected and Vp/Vs will decrease. Analyses of ultrasonic P‐ and S‐wave velocities in sands show that the Vp/Vs ratio, especially at low effective pressures, decreases rapidly with pressure. At very low pressures, Vp/Vs values can be as large as 100 and higher. Above pressures greater than 2 MPa, it plateaus and does not change much with pressure. There is significant change in signal amplitudes and frequency of shear waves below 1 MPa. The current ultrasonic data shows that Vp/Vs values can be invaluable indicators of low differential pressures.

Measurement of the shear slowness of slow formations from monopole logging-while-drilling sonic logs

Geophysics ◽  
2019 ◽  
Vol 85 (1) ◽  
pp. D45-D52
Author(s):  
Yuanda Su ◽  
Xinding Fang ◽  
Xiaoming Tang
Keyword(s):  
Numerical Modeling ◽  
Wave Velocity ◽  
Fluid Velocity ◽  
S Wave ◽  
Data Set ◽  
Acoustic Logging ◽  
Wave Velocities ◽  
Logging While Drilling ◽  
Sonic Logs ◽  
Refracted Waves

Acoustic logging-while-drilling (LWD) is used to measure formation velocity/slowness during drilling. In a fast formation, in which the S-wave velocity is higher than the borehole-fluid velocity, monopole logging can be used to obtain P- and S-wave velocities by measuring the corresponding refracted waves. In a slow formation, in which the S-wave velocity is less than the borehole-fluid velocity, because the fully refracted S-wave is missing, quadrupole logging has been developed and used for S-wave slowness measurement. A recent study based on numerical modeling implies that monopole LWD can generate a detectable transmitted S-wave in a slow formation. This nondispersive transmitted S-wave propagates at the formation S-wave velocity and thus can be used for measuring the S-wave slowness of a slow formation. We evaluate a field example to demonstrate the applicability of monopole LWD in determining the S-wave slowness of slow formations. We compare the S-wave slowness extracted from a monopole LWD data set acquired in a slow formation and the result derived from the quadrupole data recorded in the same logging run. The results indicated that the S-wave slowness can be reliably determined from monopole LWD sonic data in fairly slow formations. However, we found that the monopole approach is not applicable to very slow formations because the transmitted S-wave becomes too weak to detect when the formation S-wave slowness is much higher than the borehole-fluid slowness.

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