Waveform Matching Research Articles

Scale properties of the seismic wavefield perspectives for full-waveform matching

Starting from the nondimensionalization of equations of motion we partition the set of the velocity models in equivalence classes, such that the full waveform of an element in a given class can be calculated from the full waveform of any other element in the same class by scaling model parameters. We give a formal derivation of the seismic wavefield scale properties and we prove their capability through the use of numerical examples. Besides this, we introduce how the scale properties can be used to save computational time in full waveform modeling and inversion. In forward modeling we can use them for the calculation of the full waveform of any model in the same equivalence class of a model whose full waveform has been previously calculated. In full waveform inversion, scale properties can be used for full waveform matching: Given an experimental seismogram and a synthetic one, we can choose, in the same class of the synthetic model, another element whose waveform is closer to the experimental one.

Focal mechanism determination using high-frequency waveform matching and its application to small magnitude induced earthquakes

S U M M A R Y We present a new method using high-frequency full waveform information to determine the focal mechanisms of small, local earthquakes monitored by a sparse surface network. During the waveform inversion, we maximize both the phase and amplitude matching between the observed andmodelled waveforms. In addition, we use the polarities of the firstP-wave arrivals and the average S/P amplitude ratios to better constrain the matching. An objective function is constructed to include all four criteria. An optimized grid search method is used to search over all possible ranges of source parameters (strike, dip and rake). To speed up the algorithm, a library of Green’s functions is pre-calculated for each of the moment tensor components and possible earthquake locations. Optimizations in filtering and cross correlation are performed to further speed the grid search algorithm. The new method is tested on a five-station surface network used for monitoring induced seismicity at a petroleum field. The synthetic test showed that our method is robust and efficient to determine the focal mechanism when using only the vertical component of seismograms in the frequency range of 3–9 Hz. The application to dozens of induced seismic events showed satisfactory waveform matching between modelled and observed seismograms. The majority of the events have a strike direction parallel with the major NE–SW faults in the region. The normal faulting mechanism is dominant, which suggests the vertical stress is larger than the horizontal stress.

Matching post-Newtonian and numerical relativity waveforms: Systematic errors and a new phenomenological model for nonprecessing black hole binaries

We present a new phenomenological gravitational waveform model for the inspiral and coalescence of nonprecessing spinning black hole binaries. Our approach is based on a frequency-domain matching of post-Newtonian inspiral waveforms with numerical relativity based binary black hole coalescence waveforms. We quantify the various possible sources of systematic errors that arise in matching post-Newtonian and numerical relativity waveforms, and we use a matching criteria based on minimizing these errors; we find that the dominant source of errors are those in the post-Newtonian waveforms near the merger. An analytical formula for the dominant mode of the gravitational radiation of nonprecessing black hole binaries is presented that captures the phenomenology of the hybrid waveforms. Its implementation in the current searches for gravitational waves should allow cross-checks of other inspiral-merger-ringdown waveform families and improve the reach of gravitational-wave searches.

Comparative Power Analysis of Modular Exponentiation Algorithms

This paper proposes new chosen-message power-analysis attacks for public-key cryptosystems based on modular exponentiation, where specific input pairs are used to generate collisions between squaring operations at different locations in the two power traces. Unlike previous attacks of this kind, the new attack can be applied to all standard implementations of the exponentiation process, namely binary (left-to-right and right-to-left), m-ary, and sliding window methods. The proposed attack can also circumvent typical countermeasures, such as the Montgomery powering ladder and the double-add algorithm. The effectiveness of the attack is demonstrated in experiments with hardware and software implementations of RSA on an FPGA and a PowerPC processor, respectively. In addition to the new collision generation methods, a highly accurate waveform matching technique is introduced for detecting the collisions even when the recorded signals are noisy and there is a certain amount of clock jitter.

Waveform matching approach for fault diagnosis of a high-voltage transmission line employing harmony search algorithm

An accurate and effective technology for fault diagnosis of a high-voltage transmission line plays an important role in supporting rapid system restoration. The fault diagnosis of a high-voltage transmission line involves three major tasks, namely fault-type identification, fault location and fault time estimation. The diagnosis problem is formulated as an optimisation problem in this work: the variables involved in the fault diagnosis problem, such as the fault location, and the unknown variables such as ground resistance, are taken into account as optimisation variables; the sum of the discrepancy of the approximation components of the actual and expected waveforms is taken as the optimisation objective. Then, according to the characteristics of the formulated optimisation problem, the harmony search, an effective heuristic optimisation algorithm developed in recent years, is employed to solve this problem. Test results for a sample power system have shown that the developed fault diagnosis model and method are correct and efficient.

Detailed Waveform Inversion for Moment Tensors of M 4 Events: Examples from the Corinth Gulf, Greece

Moment tensors (MTs) of weak events are often calculated by a single agency (network), thus lacking independent validation. This article investigates how to increase reliability of the single-agency solutions through various multiple checks. It deals with the inversion of complete waveforms for six representative events (Mw 3.4-4.6) in the range of 0.08-0.15 Hz. Several three-station sets at near-regional distances (8-103 km) are used. The MTs are repeatedly calculated for two independent locations: from a regional and local network. The source depth is held fixed at the hypocenter and also grid searched to optimize the waveform match. Initially, large variations (instability) of the MT solution with the approach we used were found for some events. Later, the difficulties were understood and the solutions stabilized. It led to practical recommendations on how to detect or even avoid problematic MT solutions. First, avoid MT solutions for a single fixed depth (hypocenter). Second, optimize MT solutions by the depth grid search below epicenter (or better) for at least two alternative epicenters. Third, carefully analyze: (i) any rapid variation of the so- lution, (ii) major misfit of the first-motion polarities, (iii) low double-couple percen- tage (often correlating with (ii)), (iv) low values of the min=max eigenvalue ratio, and (v) departures of the MT-preferred depth from the location-derived depth. The MT-preferred depths, hence also the focal mechanism, may be misleading due to data problems (e.g., long-period disturbances, clipping) hidden in the band-pass wave- forms. The location-derived depth may be especially wrong for very shallow earth- quakes if the crustal model is inadequate in its shallow part and/or near stations are lacking. On the other hand, near stations (<20 km) should not be used in the wave- form inversion together with distant stations; because of their large amplitudes, the inversion can be easily biased due to instrumental data errors and small location errors. Online Material: Color figures and waveform match.

Problematic non-double-couple mechanism of the 2002 Amfilochia Mw5 earthquake, Western Greece

Two seismic agencies reported a very low double-couple percentage (DC%) of the Amfilochia earthquake, of about 30% and 60%, by Schweizerischer Erdbebendienst and Mediterranean Very Broadband Seismographic Network, respectively. Near-regional waveforms, carefully analyzed in this paper for the DC%, suggested a higher DC%, ranging from 75 to 100, dependent on the uncertainty of the source position (optimum value DC% = 93). Using a statistical F test, forward modeling of the near-regional data with a single-event low-DC% source yields a significantly worse waveform match. The fit of near-regional data can be further improved (although at the 90% significance level only) when considering a speculative two-event model. The same model, when viewed at the very-low frequency range, reaches the very low DC% values. However, two features make the two-event model unlikely: The two subevents strongly differ in their focal mechanism, and their mutual separation (3.5 s) is larger than the expected duration of this earthquake. Therefore, the two-source model appears to be nothing but an interesting equivalent representation of the non-DC model, providing some insight into the possible origin of the apparently low DC%. Preference is given to the simple interpretation, most clearly supported by the near-regional data, that the Amfilochia earthquake was an almost pure-shear event.

A High-Resolution Phase-Based Waveform Matching and Its Application to Side-Channel Attacks

This paper presents an enhanced side-channel attack using a phase-based waveform matching technique. Conventionally, side-channel attacks such as Simple Power Analysis (SPA) and Differential Power Analysis (DPA) capture signal waveforms (e.g., power traces) with a trigger signal or a system clock, and use a statistical analysis of the waveforms to reduce noise and to retrieve secret information. However, the waveform data often includes displacement errors, and this degrades the accuracy of the statistical analysis. The use of a Phase-Only Correlation (POC) technique makes it possible to estimate the displacements between the signal waveforms with higher resolution than the sampling resolution. The accuracy of side-channel attacks can be enhanced using the POC-based matching method. Also, a popular DPA countermeasure of creating distorted waveforms with random delays can be defeated by our method. In this paper, we demonstrate the advantages of the proposed method in comparison with conventional approaches of experimental DPA and Differential ElectroMagnetic Analysis (DEMA) against DES software and hardware implementations.

Relative Frequency Calibration for Fast Frequency Sweep Microwave Reflectometry

A frequency-modulated reflectometer with a frequency band of 26.5 to 40 GHz has been constructed and installed in the TST-2 spherical tokamak to measure fast density profile evolution. In order to calibrate the instantaneous frequency for various frequency sweep rates, a waveform matching method has been proposed and applied to the reflectometer. This method compares the interference patterns (i.e., waveforms) of a fixed target reflection, which do not depend on the sweep rate, and obtains the instantaneous frequency by fitting the target waveform time to the time for a reference sweep waveform. This allows evaluation of output frequency stability. The overall frequency error, including reproducibility, is around 0.1 GHz. Sweep rates up to 20 μs were used to measure the density profile evolution during rf heating.

Source-filter Comparison of Measurements of Fundamental Frequency Perturbation and Amplitude Perturbation for Synthesized Voice Signals

An investigation of the effect of glottal source aperiodicities (jitter, shimmer, and aspiration noise) on the estimation of fundamental frequency (f0) perturbation and amplitude perturbation, of synthesized, glottal source and voiced speech waveforms, is considered. Firstly, 4, cycle-event f0 estimators are examined: (1) waveform matching of the low-pass filtered waveform, (2) positive peaks (PPs) from the speech waveform, (3) PPs from the low-pass filtered waveform, and (4) positive zero crossings from the low-pass filtered waveform. The analysis shows that f0 perturbation measures taken from the low-pass filtered waveform are affected by both amplitude perturbation and random glottal noise, whereas, f0 perturbation measures taken from the PPs of the original waveform are affected by noise but not by amplitude perturbation. It is shown for the low-pass filter methods that the effects of amplitude perturbation and noise lead to increased errors in the measurement of f0 perturbation for the synthesized speech waveforms when compared with the synthesized glottal waveforms. Shimmer of the synthesized speech waveform is approximately equal to shimmer of the synthesized glottal source. However, noise and jitter affect measures of amplitude perturbation. The estimation of f0 perturbation from the synthesized speech waveform is shown to be nonlinearly related to f0 perturbation estimation from the synthesized glottal waveform as a consequence of the filtering action of the vocal tract. Low-pass filtering the voiced speech waveform is shown to provide a partial solution to this problem.

Computerized methods of analyzing faults between wells

The analysis of strata between wells is fundamental in the study of oil and gas reservoirs. Automatic analysis of strata between wells, based on stratigraphic division of well logs, is realized using computer techniques. We use a technique of dynamic waveform matching to build cross-well stratigraphic correlation relationships and automatically draw a path diagram of the cross-well stratigraphic contrast through piecewise line fitting, log character extraction, match cost calculation, and etc.. After analyzing many structure path diagrams between wells, 30 path patterns for normal faults, reverse faults, unconformities, synsedimentary faults, listric faults, pinch-outs, and so on were summarized and the path diagram patterns and correlation conceptions are presented. The application analysis in Dagang Oil Field shows that this method is effective.

Waveform analysis and delay prediction for a CMOS gate driving RLC interconnect load

This paper deals with the problem of estimating the performance of a CMOS gate driving RLC interconnect load. The widely accepted model for CMOS gate and interconnect line is used for the representation. The CMOS gate is modeled by an Alpha Power law model, whereas the distributed RLC interconnect is represented by an equivalent π-model. The output waveform and the propagation delay of the inverter are analytically calculated and compared with SPICE simulations. The analytical driver-interconnect load model gives sufficiently close results to SPICE simulations for two different cases of slow and fast input ramps. For each case of stimulation, the model gives an insight to four regions of operation of the CMOS gate. The voltage waveform at the end of an interconnect line is obtained for each region of operation. The SPICE and analytical results for the output voltage waveform and propagation delay match very closely.

Calibration of the Tibetan Plateau Using Regional Seismic Waveforms

We use the recordings from 51 earthquakes produced by a PASSCAL deployment in Tibet to develop a two-layer crustal model for the region. Starting with their ISC locations, we iteratively fit the P-arrival times to relocate the earthquakes and estimate mantle and crustal seismic parameters. An average crustal P velocity of 6.2–6.3 km/s is obtained for a crustal thickness of 65 km while the P velocity of the uppermost mantle is 8.1 km/s. The upper layer of the model is further fine-tuned by obtaining the best synthetic SH waveform match to an observed waveform for a well-located event. Green's functions from this model are then used to estimate the source parameters for those events using a grid search procedure. Average event relocation relative to the ISC locations, excluding two poorly located earthquakes, is 16 km. All but one earthquake are determined by the waveform inversion to be at depths between 5 and 15 km. This is 15 km shallower, on average, than depths reported by the ISC. The shallow seismicity cut-off depth and low crustal velocities suggest high temperatures in the lower crust. Thrust faulting source mechanisms dominate at the margins of the plateau. Within the plateau, at locations with surface elevations less than 5 km, source mechanisms are a mixture of strike-slip and thrust. Most events occurring in the high plateau where elevations are above 5 km show normal faulting. This indicates that a large portion of the plateau is under EW extension.

The detection of low magnitude seismic events using array-based waveform correlation

It has long been accepted that occurrences of a known signal are most effectively detected by cross-correlating the incoming data stream with a waveform template. Such matched signal detectors have received very little attention in the field of detection seismology because there are relatively few instances in which the form of an anticipated seismic signal is known a priori. Repeating events in highly confined geographical regions have been observed to produce very similar waveforms and good signals from events at a given site can be exploited to detect subsequent co-located events at lower magnitudes than would be possible using traditional power detectors. Even greater improvement in signal detectability can be achieved using seismic arrays; running correlation coefficients from single sensors can be stacked over an array or network to result in a network correlation coefficient displaying a significant array gain. If two events are co-located, the time separating the corresponding patterns in the wave train as indicated by the cross-correlation function is identical for all seismic stations and this property means that the correlation coefficient traces are coherent even when the waveforms are not. We illustrate the power of array-based waveform correlation using the 1997 August 16 Kara Sea event. The weak event that occurred 4 hr after the main event was barely detected using an STA/LTA detector on the SPITS array but is readily detected by signal matching on a single channel. The main event was also recorded by the far more distant NORSAR array but no conventional detection can be made for the second event. A clear detection is, however, made when the correlation coefficient traces are beamformed over all sensors of the array. We estimate the reduction in detection threshold of a test signal on a regional seismic array using waveform correlation by scaling down a master signal and immersing it into seismic noise. We show that, for this case, waveform correlation using a single channel detects signals of approximately 0.7 orders of magnitude lower than is possible using an STA/LTA detector on the array beam. Waveform matching on the full array provides an additional improvement of approximately 0.4 magnitude units. We describe a case study in which small seismic events at the Barentsburg coal mine on Spitsbergen were detected using the signals from a major rockburst as master waveforms. Many spurious triggers occurred in this study whereby short sections of signal exhibited coincidental similarity with unrelated incoming wave fronts. We demonstrate how such false alarms can almost always be identified and screened out automatically by performing frequency–wavenumber analysis upon the set of individual correlation coefficient traces.

Estimating the orientation error of the Dahan Downhole Accelerometer using the maximum cross-correlation coefficient between the observed and synthetic waves

A new algorithm to correct the orientation error of the accelerometerat the Dahan Downhole Array, Hualien, Taiwan is developed. This algorithmconsists of three stages: (1) rotating two horizontal ground motions on thefree surface to the SH-SVdirection and SH axis offers a reference direction.(2) computing the synthetic downhole SH waves at a downhole station and (3)searching a rotation angle for downhole observation that yields a best waveformmatch between the synthetic and observed downhole seismograms. At this point, the rotated angle corresponding to the best waveform match can be considered as the orientation error. We selected five earthquakes with good data qualityfor analysis. Results show that this algorithm gives a more stable estimationthan a conventional method because it allows the selection of data from a wider time window for analyses. The estimated orientation error of the accelerometers at the Dahan Downhole Array after the 1999 reinstallation are40°, 114° and 285° at depths of 50, 100 and 200 m, respectively.

誘導波解析によるＰＣ鋼線の遅れ破壊の動的破壊過程

This paper presents new methods for source location and fracture dynamics study of guided waves produced by the delayed fracture of a pre-stressed concrete (PC) steel wire. Utilizing the guided wave produced by laser ultrasonic system, the author first proposed a new source location method of guided waves in the PC wire of 7mm diameter. Source location in the transverse section was determined from the amplitude ratio of the maximum peak of flexural (F-) mode to that of first arrival longitudinal (L-) mode. Location in the axial direction was determined from the time difference between the first arrival L-mode and the peak arrival time of the F-mode. Estimated progression of micro-cracks agreed well with characteristic features observed on fracture surface. Dynamics of micro-cracks were estimated by the waveform matching of the first packet of the L-mode to the monitored one and found to be generated within 0.5 microseconds.

A quick search algorithm for acoustic signals using histogram features—time‐series active search

AbstractProposed here is an algorithm that offers quick detection and location of a target acoustic signal, such as a specific theme song or commercial in a long broadcast. With previous search techniques based on shifted matching of spectra or waveforms, searching through a long signal required enormous computation. On the other hand, with the proposed algorithm, considerable time saving is obtained by using a skipping technique in the histogram‐based search. For example, in experiments on a workstation, when spectral features were preliminarily extracted from acoustic signals, successful search for a target signal (15 s) in a 6‐h signal took only about 2.3 s. In addition, the proposed algorithm proved robust to white Gaussian noise even at a S/N ratio of 20 dB. © 2001 Scripta Technica, Electron Comm Jpn Pt 3, 84(12): 40–47, 2001

Acoustic waveform inversion with application to seasonal snow covers.

The amplitude and waveform shape of atmospheric acoustic pulses propagating horizontally over a seasonal snow cover are profoundly changed by the air forced into the snow pores as the pulses move over the surface. This interaction greatly reduces the pulse amplitude and elongates the waveform compared to propagation above other ground surfaces. To investigate variations in snow-cover effects, acoustic pulses were recorded while propagating horizontally over 11 different naturally occurring snow covers during two winters. Two inversion procedures were developed to automatically match the observed waveforms by varying the snow-cover parameters in theoretical calculations. A simple frequency-domain technique to match the dominant frequency of the measured waveform suffered from multiple solutions and poor waveform matching, while a time-domain minimization method gave unique solutions and excellent waveform agreement. Results show that the effective flow resistivity and depth of the snow are the parameters controlling waveform shape, with the pore shape factor ratio of secondary importance. Inversion estimates gave flow resistivities ranging from 11 to 29 kN s m(-4), except for two late-season cases where values of 60 and 140 were determined (compared to 345 for the vegetation-covered site in the summer). Acoustically determined snow depths agreed with the measured values in all but one case, when the depth to a snow layer interface instead of the total snow depth was determined. Except for newly fallen snow, the pore shape factor ratio values clustered near two values that appear to correspond to wet (1.0) or dry (0.8) snow.

Evidence for temporal variation of seismic velocity within the upper continental crust

Observations of systematic temporal variations of seismic anisotropy are presented for an induced‐seismicity experiment at 9 km depth. These observations were made under particularly well‐controlled conditions in the German Continental Deep Drilling Program (KTB) borehole, using shear wave splitting from similar events recorded at a three‐component instrument located at 4 km depth from a hydraulic fracturing experiment at 9 km depth. In a large set of seismic events recorded during the experiment, many can be associated with multiplets exhibiting essentially identical waveforms. Since they must have approximately the same source location and source radiation pattern, these events are particularly useful for testing the hypothesis of time‐dependent anisotropy. Anisotropy itself is clearly a very prominent feature in the data. A simple approach for waveform matching of split shear waves allows unprecedented resolution of variations in shear wave splitting. Importantly, the variation of shear wave splitting with time is a relative measurement, which can be performed with higher accuracy than the associated absolute measurement. In particular, the relative measurement is not affected by timing errors nor by event distance variations. During the experiment the difference between shear wave velocities decreases by ∼2% within ∼12 hours. After that, the medium apparently approaches a state which is stable for at least 5 hours. We suggest that the temporal variation is due to the tectonic stress release from seismic events caused by the fluid injection. This model requires the presence of fluid‐filled cracks at depths larger than 4 km.

Mantle variation within the Canadian Shield: Travel times from the portable broadband Archean‐Proterozoic Transect 1989

We report travel times from the Archean‐Proterozoic Transect 1989. This type of data set recorded by a transect of portable broadband instruments allows us to make inferences about mantle structure in the region between the Wyoming Craton and the Superior Province of the Canadian Shield. With station separations of 50 to 100 km and frequencies up to 5 Hz the resolution of lateral changes is increased by nearly an order of magnitude over previous studies to a scale that allows us to study the relation between velocity variation in the continental upper mantle, surface geology, tectonic features and age provinces. Travel times of direct and later phases are obtained from waveform matching. The values are corrected for crustal contribution and inverted for the vertical path upper mantle delay δtUM under each station as well as the azimuthal dependence of this quantity. The prominent feature in the upper mantle delays δtUM is the variation by at least 1.5 s for S, much of which occurs over a narrow zone of just a few hundred kilometers width. This suggests a major lateral upper mantle transition which does not coincide with the surface geological edge of the Canadian Shield but is located within the shield. This same transition is also observed in shear wave splitting delay times. Surprisingly, however, the P delays do not exhibit a corresponding variation. We address this apparent contradiction and show how it may be explained in conjunction with anisotropy in the subcontinental lithosphere. A simplified thermal model of the lithospheric transition zone, in which temperature controls the degree of crystallographic alignment and thus seismic anisotropy, predicts this phenomenon.