Wave Travel Times Research Articles

Towards consideration of epistemic uncertainty in shear-wave velocity measurements obtained via seismic cone penetration testing (SCPT)

Seismic cone penetration testing (SCPT) is a powerful geotechnical site characterization tool, allowing for simultaneous collection of routine cone penetration testing data and rapid downhole-type measurements of shear-wave velocity (VS). However, the uncertainties associated with developing VS profiles from SCPT measurements are rarely considered or communicated to the end-user. One important source of VS uncertainty is related to how the shear wave travel times are interpreted from the recorded waveforms, while another critical source of uncertainty is related to the analysis method used to transform the travel times to velocities. In this study, four common ways of obtaining travel times were considered: (i) first arrival picks, (ii) peaks and troughs picks, (iii) crossover picks, and (iv) the peak response of the cross-correlation function. Using these different travel times, a number of VS profiles were developed using four different velocity analysis methods: (i) pseudo-interval, (ii) true-interval, (iii) corrected vertical travel time slope-based, and (iv) raytracing. Through consideration of multiple wave arrival time and velocity analysis methods, a robust and meaningful quantification of the intramethod, depth-dependent epistemic uncertainty in VS obtained from several example SCPT datasets has been developed. VS uncertainty is further examined through consideration of the intermethod variability and bias between SCPT and direct-push crosshole testing.

A Numerical Method of Determining Permittivity from the Modulus of the Electric Intensity Vector of an Electromagnetic Field

The system of equations of electrodynamics is considered for a nonmagnetic nonconducting medium. For this system, the problem is under study of determining the permittivity e from the given modulus of the electric intensity vector of the electromagnetic field that is the result of the interference of the two fields generated by some point sources of an extraneous current. It is assumed that permittivity is different from a given positive constant e0 only inside a compact domain Ω0 ⊂ ℝ3, whereas the modulus of the electric field intensity vector is given for all frequencies starting from a fixed frequency ω0 on the boundary S of some domain Ω that includes Ω0. It is shown that this information allows us to reduce the original problem to the well-known inverse kinematic problem of determining the refraction index inside Ω by the travel time of the electromagnetic wave between the points of the boundary of this domain. The algorithm for numerical solution of the inverse problem is constructed, and the test calculations on the simulated data are presented.

ANOMALOUS ERRORS IN DETERMINING FOCUS COORDINATES EARTHQUAKES AND SUGGESTIONS FOR THEIR ELIMINATION

Objectives The aim of the study is to develop a method for estimating the speed of seismic waves in different directions of propagation and by taking into account the dimensions of the focus, reducing the error in determining the coordinates of the hypocenter. Method To find the hypocenter of the earthquake, the data of the seismic wave velocities, the differences in the times of arrival of seismic waves on seismic sensors and the error in determining the time difference are used. The data with an error determine the coordinates of the hypocenter using information from various combinations of seismic sensors. Processing the resulting array of coordinates, estimates the seismic wave velocities / or determines the spatial shape of the earthquake source and the coordinates of the hypocenter. According to the coordinates of the cinema center, the differences in the travel time of seismic waves are corrected and the distances to the seismic sensors are refined. Results After preliminary determination of the coordinates and shape of the earthquake source, if there are a large number of seismic sensors, it is possible to clarify the coordinates of the earthquake hypocenter taking into account the recommendations given in the works. Conclusion Using the proposed method implies the presence of a large number of sensors to determine the complex shape, the earthquake source.

3D Modeling and Volume Estimation of Riverbed Layers Based on Sub Bottom Profiler Measurement Data

The river is one of the transportation routes for human beings, as well as the pipelines for oil and gas distribution, or as power cable lines and communications networks. In order to not disturb the pipe or cable due to the activity of the ship through the river, it is necessary to study the sediment from the river. This study aims to determine the type of sediment, the thickness of the sediment, the depth of sediment, and volume of the sediment itself. It can be done with acoustic measurements.The measurement of the acoustic survey in this activity uses a sub bottom profiler Strata Box HD type Chirp. By using this tool, it can obtain sediment layer up to a certain depth. The result of the measurement will be interpreted to obtain the travel time of the acoustic wave as it reflected on the sediment layer. The travel time than processed and corrected with the tidal measurement data which made over 14 days to obtain the actual depth value from the result with the sub bottom profiler. The depth data then were quality tested based on reference IHO SP-44 2008 at order 1a.This activity produces a 3D model of river layer, depth profile and sediment layer volume estimation. The result of the quality tested obtained corrected depth data has met the established standards of order 1a IHO SP-44 2008. Using a 95% confidence level, the test results in the first layer is 0.271 m with an error tolerance at 0.510 m. For the second layer has a data quality test results 0.491 m with a tolerance at 0.521 m. The result of depth profile is a long section and cross section. The long section indicates that in the deflection of the river area there is a steep decline compared to the area before and after the river deflection. In addition, the river deflection area has a thinner sedimentary layer. The volume estimation of sediment layers obtained in the area of the activity is 4932752.739 m3.

Propagation of Surface Waves in Asphalt Pavements Generated by Different Load Impulse of Falling Weight Deflectometer

Abstract The propagation of waves generated by load impulse of two FWD types was assessed using test outputs in the form of time history data. The calculated travel time of wave between the receiver in the centre of load and others receivers showed the contradiction with the theory as for the receivers up to 600 (900) mm from the centre of load. Therefore, data collected by the sensors positioned at the distance of 1200 and 1500 mm were used. The influence of load magnitude on the waves propagation was investigated via the different load force with approximately the same load time and vice versa. Expectations relating to the travel time of waves, depending on the differences of load impulse, were not met. The shorter travel time of waves was detected in the case of the lower frequencies. The use of load impulse magnitude as a possible explanation was not successful because opposite tendencies in travel time were noticed.

On the Influence of Upstream Flow Contributions on the Basin Response Function for Hydrograph Prediction

AbstractSpatially distributed travel time (SDTT) methods have been developed as an alternative to semidistributed and fully distributed methods for rainfall‐runoff modeling. In these methods, the travel times of grid cells are summed along flow paths and then convoluted to generate the hydrograph at the outlet. One central aspect of SDTT models that remains partially addressed is the effect of upstream flow contributions and their dynamics on the calculated flood wave travel times. Some methods neglect upstream contributions, but these are known to produce incorrect representations of the hydrological response. Other methods assume static upstream contributions, but the reliability of this approximation is poorly understood. In this study, we develop a new travel time method that accounts for dynamic upstream contributions. We test our method in three synthetic basins generated with a landscape evolution model that allows explicit control of primary watershed characteristics. We evaluate the method's performance for different storms by comparing its response to that produced by a fully distributed kinematic wave model. Furthermore, the method is tested in a real basin. We also analyze the dynamic behavior of the upstream contribution and travel times within the synthetic basins. Results show that existing static upstream contribution approaches in SDTT models do not adequately reproduce the hydrographs from the fully distributed kinematic wave model nor the observed hydrograph of the real basin. The proposed method improves the reproduction of hydrograph peak flows and temporal variability. Furthermore, the instantaneous unit hydrographs produced by the new method exhibit more positive skewness than the static approximations.

P and S wave travel time tomography of the SE Asia-Australia collision zone

The southeast (SE) Asia - Australia collision zone is one of the most tectonically active and seismogenic regions in the world. Here, we present new 3-D P- and S-wave velocity models of the crust and upper mantle by applying regional earthquake travel-time tomography to global catalogue data. We first re-locate earthquakes provided by the standard ISC-Reviewed and ISC-EHB catalogues using a non-linear oct-tree scheme. A machine learning algorithm that clusters earthquakes depending on their spatiotemporal density was then applied to significantly improve the consistency of travel-time picks. We used the Fast Marching Tomography software package to retrieve 3-D velocity and interface structures from starting 1-D velocity and Moho models. Synthetic resolution and sensitivity tests demonstrate that the final models are robust, with P-wave speed variations (~130 km horizontal resolution) generally recovered more robustly than S-wave speed variations (~220 km horizontal resolution). The retrieved crust and mantle anomalies offer a new perspective on the broad-scale tectonic setting and underlying mantle architecture of SE Asia. While we observe clear evidence of subducted slabs as high velocity anomalies penetrating into the mantle along the Sunda arc, Banda arc and Halmahera arc, we also see evidence for slab gaps or holes in the vicinity of east Java. In the Banda arc, we image the slab as a single curved subduction zone. Furthermore, a high-velocity region in the mantle lithosphere connects northern Australia with Timor and West Papua. The S-wave model shows broad-scale features similar to those of the P-wave model, with mantle earthquakes generally distributed within high-velocity slabs. The high velocity mantle connection between northern Australia and the eastern margin of the Sunda arc is also present in the S-wave model. While the S-wave model has a lower resolution than the P-wave model due to the availability of fewer paths, it nonetheless provides new and complementary insights into the structure of the upper mantle beneath southeast Asia.

Travel Time Tomography

We survey some results on travel time tomography. The question is whether we can determine the anisotropic index of refraction of a medium by measuring the travel times of waves going through the medium. This can be recast as geometry problems, the boundary rigidity problem and the lens rigidity problem. The boundary rigidity problem is whether we can determine a Riemannian metric of a compact Riemannian manifold with boundary by measuring the distance function between boundary points. The lens rigidity problem problem is to determine a Riemannian metric of a Riemannian manifold with boundary by measuring for every point and direction of entrance of a geodesic the point of exit and direction of exit and its length. The linearization of these two problems is tensor tomography. The question is whether one can determine a symmetric two-tensor from its integrals along geodesics. We emphasize recent results on boundary and lens rigidity and in tensor tomography in the partial data case, with further applications.

Analogue stochastic gravity phenomena in two-component Bose-Einstein condensates: Sound cone fluctuations

We investigate the properties of the condensates of cold atoms at zero temperature in the tunable binary Bose-Einstein condensate system with a Rabi transition between atomic hyperfine states. We use this system to examine the effect of quantum fluctuations in a tunable quantum gas on phonon propagation. We show that the system can be represented by a coupled two-field model of a gapless phonon and a gapped mode, which are analogous to the Goldstone and Higgs particles in particle physics. We then further trace out the gapped modes to give an effective purely phononic theory using closed-time-path formalism. In particular, we are interested in the sound cone fluctuations due to the variation of the speed-of-sound acoustic metric, induced by quantum fluctuations of the gapped modes. These fluctuations can be interpreted as inducing a stochastic space-time, and thus are regarded as analogue phenomena of light cone fluctuations presumably arising from quantum gravity effects. The effects of fluctuations can be displayed in the variation in the travel time of sound waves. We suggest the relevant experiments to discuss the possibility of experimental observations.

Three‐Dimensional Basin and Fault Structure From a Detailed Seismic Velocity Model of Coachella Valley, Southern California

AbstractThe Coachella Valley in the northern Salton Trough is known to produce destructive earthquakes, making it a high seismic hazard area. Knowledge of the seismic velocity structure and geometry of the sedimentary basins and fault zones is required to improve earthquake hazard estimates in this region. We simultaneously inverted first P wave travel times from the Southern California Seismic Network (39,998 local earthquakes) and explosions (251 land/sea shots) from the 2011 Salton Seismic Imaging Project to obtain a 3‐D seismic velocity model. Earthquakes with focal depths ≤10 km were selected to focus on the upper crustal structure. Strong lateral velocity contrasts in the top ~3 km correlate well with the surface geology, including the low‐velocity (<5 km/s) sedimentary basin and the high‐velocity crystalline basement rocks outside the valley. Sediment thickness is ~4 km in the southeastern valley near the Salton Sea and decreases to <2 km at the northwestern end of the valley. Eastward thickening of sediments toward the San Andreas fault within the valley defines Coachella Valley basin asymmetry. In the Peninsular Ranges, zones of relatively high seismic velocities (~6.4 km/s) between 2‐ and 4‐km depth may be related to Late Cretaceous mylonite rocks or older inherited basement structures. Other high‐velocity domains exist in the model down to 9‐km depth and help define crustal heterogeneity. We identify a potential fault zone in Lost Horse Valley unassociated with mapped faults in Southern California from the combined interpretation of surface geology, seismicity, and lateral velocity changes in the model.

Pulse X-ray Device Based on a Combined Spiral Generator

A prototype of a pulsed X-ray machine with an operating voltage of 600–800 kV based on a combined spiral generator has been manufactured and tested. Compared to the classical spiral generator, the total length of the spiral winding is increased by adding one-line winding coils in order to match the wave travel time along the spiral generator line to the oscillation time in the generator according to the Tesla model. As a result, a high efficiency was obtained in this modification of the transformer. A theoretical model describing the operation of the combined generator is proposed.

Non-destructive Method for Evaluating Grouted Ratio of Soil Nail Using Electromagnetic Wave

Although soil nails have been widely used for stabilizing slopes, they are often only partially grouted. Thus, grouted ratio of soil nails should be evaluated to prevent landslides. The purpose of this study was to investigate the suitability of a non-destructive method using electromagnetic waves for evaluating grouted ratio of soil nails. Experimental studies were performed with steel bars, partially grouted steel bars, and fully grouted steel bars in air. Partially and fully grouted steel bars were also installed in soils to simulate soil nails installed on slopes. Electromagnetic waves were generated and received using a time domain reflectometer by configuring a two-conductor transmission line formed by two parallel steel bars or two parallel grouted steel bars. Results of experiments showed that the respective round-trip travel time of electromagnetic waves increased with increasing length of the steel bar, grouted steel bar in air, and grouted steel bar in soils. The velocity of electromagnetic waves was the greatest in steel bars but the lowest in grouted steel bars in soils. In addition, the velocity of the electromagnetic waves decreased with increasing grouted ratio. This study suggests that electromagnetic waves might be useful for evaluating grouted ratios of soil nails to stabilize slopes.

An Analysis of the Accuracy of Time Domain 3D Image Geology Model Resulted from PSTM and Depth Domain 3D Image Geology Model Resulted from PSDM in Oil and Gas Exploration

This study aims to obtain a geological model which is close to the truth and compare accuracy between the time domain 3D image of the PSTM results with the depth domain 3D image of PSDM results. There are 3 parameters to determine the accuracy of an interval velocity model in the production of a geology model: depth gathering that is already flat, semblance that has concurred with zero residual move-out axes, and depth image which conforms to the marker (well seismic tie). The analytical method employed is Horizon Based Tomography, which is a method to correct the seismic wave travel time error along the analyzed horizon. Reducing errors in the travel time of the seismic wave will decrease depth errors. This improvement is expected to provide correct information about subsurface geological conditions. The results showed that the depth domain image generated by the PSDM process represents the actual geological model better than time domain image produced by the PSTM process, evidenced by the sharpening of the reflector continuity, reduction of pull-up effect, and high resolution.

Investigation of Uncertain Factors on Measuring Residual Stress with Critically Refracted Longitudinal Waves

Critically refracted longitudinal (LCR) waves are commonly used to evaluate the residual stress of a material. The utilization of LCR waves is advantageous in that these waves are not sensitive to the texture of the material. Thus, LCR can be considered as a bulk longitudinal mode and can penetrate into the material well below its surface. However, while measuring the residual stress, the precision of the LCR wave travel-time is influenced by several uncertain factors. In order to further improve the accuracy of test results, we developed a measurement approach based on three aspects. First, the distances between the transmitter and the receivers were determined by transducer signal analysis. Second, for the residual stress detection to be consistent, transducers with different frequencies presented similar beam divergence angles. Finally, three different frequencies were used to evaluate the residual stress throughout the plate thickness. Based on the results of the above analysis, we used LCR waves to test 304 stainless steel plates. The detection error of residual stress measurement was ca. ±23 MPa. When compared with the X-ray diffraction approach, our method showed similar trends for the same regions of the specimens.

Sub-vertical low-velocity zone from P and S wave local tomography of the aftershock sequence of the Mw5.9 Chenoua (Algeria) earthquake of October 29, 1989: relict of the Miocene Eurasia–Africa suture zone?

Travel time data from the aftershock sequence following the Mw5.9 Chenoua earthquake of October 29, 1989 are inverted to obtain a three-dimensional tomographic image of the region. The data are P and S wave travel times obtained from 394 carefully selected aftershocks recorded at 18 temporary stations between November 7 and 18, 1989. A three-dimensional P wave velocity model down to a depth of 10 km is obtained. At shallow depth, the velocity contrasts clearly outline the Plio-Quaternary sedimentary basins separated by the Chenoua bedrock high. Below 4 km, a sub-vertical east–west low-velocity zone can be seen down to the limit of the resolved model. The fault activated during the Chenoua event, as depicted by the aftershocks distribution is oblique to this structure and north of it. The location and geometry of the low-velocity zone suggest it may correspond to a structure belonging to the suture between Eurasia and Africa, a former north dipping subduction zone, now a block boundary inherited from the Miocene collision phase. This structure may partly constrain the shallower deformation and could be responsible of the localized Sahel anticline north of the stable Mitidja basin.

Sound velocities of the 23 Å phase at high pressure and implications for seismic velocities in subducted slabs

Dense hydrous magnesium silicates (DHMS) are believed to play an important role in transporting water back into the deep interior of the Earth. Recently, a new Al-bearing hydrous Mg-silicate, named the 23 Å phase [ideal composition Mg12Al2Si4O16(OH)14], was reported (Cai et al., 2015), which could be another important hydrous phase in subducting slabs. In this paper, we report new measurements of the compressional (P) and shear (S) wave velocities of the 23 Å phase under pressures up to 14 GPa at room temperature, using a bulk sample with a grain size of less than 20 μm and density of 2.947 g/cm3. The acoustic measurements were conducted in a 1000-ton uniaxial split-cylinder multi-anvil apparatus using ultrasonic interferometric techniques (Li et al., 1996). The pressures were determined in situ by using an alumina buffer rod as the pressure marker (Wang et al., 2015). A dual-mode piezoelectric transducer enabled us to measure P and S wave travel times simultaneously, which in turn allowed a precise determination of the sound velocities and elastic bulk (KS) and shear (G) moduli at high pressures. The velocities of this 23 Å phase (ambient VP = 7.53 km/s, VS = 3.72 km/s) are lower than those of phase A, olivine, pyrope, etc. (especially for S waves), yet the VP/VS ratio (from 2.02 to 1.94, decreasing with increasing pressure) is much higher compared to those mantle minerals (1.7–1.8). A fit to the acoustic data using finite strain analysis combined with the Hashin-Shtrikman (HS) averaging scheme yields: KS0 = 111.4(6) GPa, G0 = 41.0(2) GPa, and KS′ = 3.6, G′ = 1.8 for the bulk and shear moduli and their pressure derivatives. Using these data, the density and velocity profiles of the hydrous harzburgite and lherzolite were calculated along a warm slab P-T condition. The results suggest that a hydrous pyrolitic assemblage containing 23 Å phase should be distinguishable from a dry assemblage at the high pressure and temperature conditions relevant to Al-bearing subducted slabs.

IDENTIFCATION OF HIGH VELOCITY ANOMALIES, IMPERCEPTIBLE TO SEISMIC RESOLUTION, BY INTEGRATION OF SEISMIC ATTRIBUTES, IN PENOBSCOT FIELD, CANADA

Penobscot Field is located in the Sable Sub-basin, in the Nova Scotia Basin, belonging to the Canadian territory, and for the year of 1991, a 3D seismic acquisition was carried out in this region. Also, two exploratory wells were previously drilled (L-30 and B-41). Then, with the subsequent interpretation of the area, a discrepancy was found around 10ms to 15ms (approximately 25m) in the travel times of the seismic waves in the vicinity of well B-41, resulting in a false structural high in the Mississauga Formation and Naskapi Member. It is possibly caused by changes in geological facies and thickness of the Wyandot formation, consequently, B-41 well became dry. For these reasons, to identify the possible problem which caused everything mentioned above, the area between the wells was delimited by a seismic subvolume (by reducing the seismic cube), making a seismic interpretation of the top of the formations of interest, as well as an analysis of certain petrophysical properties in the wells, in order to delimit the thickness of the anomaly and, consecutively, the use of the seismic attributes for lateral identification of the anomaly in the Wyandot Formation.

SOLUTION OF HIGH VELOCITY ANOMALIES IMPERCEPTIBLE TO SEISMIC RESOLUTION, BY MEANS OF SYNTHETIC MODELS, PENOBSCOT FIELD, CANADA

Penobscot Field is located in the Sable Sub-basin in Nova Scotia, Canada, where a 3D seismic acquisition campaign was carried out in 1991 and also two oil wells were previously drilled (L-30 and B-41). In the interpreted seismic data, a discrepancy was found in the travel times of the seismic waves near well B-41, causing a false structural height in the Naskapi Member, Mississauga Formation (Early Cretaceous or Lower Cretaceous) and deeper formations (10 to 15 ms, i.e. approximately 25 m). It was decided to find a solution of this problem using synthetic models. First, making a delimitation of the study area by means of a seismic subcube, which were later interpreted surfaces of interest, through the well data. The average velocity and density properties were found for each interpreted strata. Subsequently, a 2D seismic acquisition was simulated, choosing a line that crossed both wells and through the use of ray traces, synthetic shot gathers were obtained and processed through the use of different seismic migration tests, and the final solution was found to be Kirchhoff pre-stacking migration in depth.

P Wave Azimuthal Anisotropic Tomography in Northern Chile: Insight Into Deformation in the Subduction Zone

AbstractBased on a large data set of local body wave travel times, we determined the first 3‐D model of azimuthal P wave anisotropic tomography of northern Chile in order to study the deformation in the subduction zone. Our results indicate different deformation patterns in the overriding lithosphere, mantle wedge, and the subducting Nazca slab as well as significant along‐arc variations. Radiating fast velocity directions (FVDs) around the rupture zone of the 2014 Iquique earthquake (Mw 8.2) are notable in the crust, which may reflect the specific crustal extension induced by a point‐like stress source in the form of a fully locked asperity at the plate interface. In most of the study region, FVDs in the mantle wedge are trench normal, which we interpret to have resulted from mantle wedge flow driven by the oceanic plate subduction. However, trench‐parallel FVDs are found beneath the northern segment, which may imply the occurrence of B‐type olivine fabrics in the cold forearc mantle. Strong along‐arc variations are also observed in the subducting slab, which may reflect intraslab heterogeneity and change in the slab geometry. In the northern segment, slab bending induces generally trench‐normal extension and leads to trench‐normal FVDs in the upper part of the slab. In contrast, in the southern segment, flat slab subduction and thus slab unbending dominate, producing trench‐normal compression and trench‐parallel FVDs instead. Along the subducting slab interface, FVDs change from trench‐parallel to trench‐normal in the downdip direction, which may indicate the first‐order transition from compression in the locking area to dominant shear in the decoupling area along the slab interface.

Seismic Evidence for a Mantle Transition Zone Origin of the Wudalianchi and Halaha Volcanoes in Northeast China

AbstractThere exists much debate about origins of Cretaceous to present volcanism in northeast (NE) China. Here we present high‐resolution seismic images of the upper mantle beneath NE China obtained by inverting P wave traveltime data recorded by two dense linear arrays. The inclusion of the new data set has greatly improved sampling of the upper mantle beneath the study region, providing tight constraints on the seismic structure under the intraplate Wudalianchi and Halaha volcanoes. Local‐scale low P wave velocity (low‐Vp) anomalies are revealed in the shallow mantle beneath the two volcanoes, whereas a large‐scale high‐Vp zone is imaged in the mantle transition zone. These new results suggest that the two volcanoes, though located at different sites above the stagnant Pacific slab in the mantle transition zone, are likely related to the deep subduction and dehydration of the Pacific slab, possibly through hot and wet upwelling in the big mantle wedge beneath Wudalianchi and through deeper hydrous upwelling related to slab avalanche beneath Halaha. Our results also reveal other striking features, such as high‐Vp anomalies resting atop the 410‐km discontinuity beneath the Great Xing'an Range and the Songliao Basin, which are attributed to detached continental lithosphere. The delamination most likely occurred in the Cretaceous, which induced widespread magmatism in NE China.