Seismological studies at Parkfield IV: Variations in controlled-source waveform parameters and their correlation with seismicity, 1987 to 1995

1997 ◽  
Vol 87 (1) ◽  
pp. 39-49 ◽  
Author(s):  
E. Karageorgi ◽  
T. V. McEvilly ◽  
R. Clymer
Keyword(s):  
Wave Field ◽  
Travel Time ◽  
Fault Zone ◽  
Water Levels ◽  
Deep Penetration ◽  
Fault Creep ◽  
Data Set ◽  
Spectral Content ◽  
S Waves ◽  
Earthquake Sequences

Abstract Since June 1987 at Parkfield, California, the 10-station borehole network of three-component sensors has been illuminated 52 times using a shear-wave vibrator in three orientations at up to eight source points, in a search for temporal changes in elastic wave P and S velocities, anisotropy, or attenuation. The monitoring interval includes the beginning and end of a severe 3-yr drought and four earthquake sequences, two of which produced the only A-level alerts to date in the Parkfield Prediction Experiment. A comprehensive study of the entire data set reveals a progressive travel-time advance in the coda of S waves propagating in a localized region southeast of Middle Mountain. The anomalous wave field exhibits high apparent velocities, suggesting deep penetration of the fault zone, although similar changes are not seen in waveforms from repeating similar microearthquakes. Accompanying the changes in travel time were systematic variations in spectral content and polarization of the same segments of the wave field. These variations correlate well in time and space with significant features of seismicity, fault creep, and water levels at Parkfield. A preferred mechanism for the phenomenon is changing hydrologic conditions along the affected stretch of the fault zone, possibly deformation-induced, that perturb the shallow-propagating S coda in the upper few hundred meters of section.

Seismological studies at Parkfield. II. Search for temporal variations in wave propagation using vibroseis

1992 ◽  
Vol 82 (3) ◽  
pp. 1388-1415
Author(s):  
E. Karageorgi ◽  
R. Clymer ◽  
T. V. McEvilly
Keyword(s):  
Travel Time ◽  
Fault Zone ◽  
High Sensitivity ◽  
Temporal Variations ◽  
Nucleation Site ◽  
Elastic Response ◽  
S Wave ◽  
Near Surface ◽  
S Waves ◽  
Shallow Subsurface

Abstract For more than 3 years the propagation characteristics of shear waves have been monitored for paths near the 1966 hypocenter at Parkfield, the presumed nucleation site for the expected next M6 earthquake there. Data have been collected repeatedly (33 sets as of April 1991) from eight S-wave Vibroseis source positions into the 10 borehole-installed three-component seismometers of the local high-sensitivity digital network. Twenty-second correlated records from a 6- to 24-Hz sweep are acquired, and the entire seismogram is viewed for analysis as the elastic response of the local crustal structure, which includes the San Andreas fault zone. Amplitudes, travel times, spectra, and particle motions of the P and S waves are monitored for indications of any changes in these properties that may be attributed to processes associated with nucleation. The horizontal vibrator at each source point is positioned at three surface-orientations to study anisotropy. Unorthodox methods have been developed to display the waveform properties in time in order to visualize the resulting massive data sets. The first-order variations seen in some of the parameters are attributed to changes from dry to wet conditions in the shallow subsurface due to the seasonal rainfall, which affects the source function of the vibrator. Corrections have been devised for these source-specific variations. Secular variations not obviously coupled to seasonal near-surface changes are also seen in some localized time intervals within the 20-sec records. The most striking of such changes is a progressive travel-time decrease at rates of 3 to 7 msec / year seen for late arrivals (7 to 11 sec travel time) on at least five paths into station VCA, which sample the region southeast of the anticipated epicenter at Middle Mountain. This anomaly appears to be genuine and is now the subject of intensified study. In the same general area, along the fault in the southwestern block, the direct S wave is clearly split, with the faster of the split phases polarized parallel to the fault zone, a result in agreement with that from the VSP survey in the Varian well on the northeast side of the fault.

A regularized continuum model for fault zones with rate and state friction

2021 ◽  
Author(s):  
Mohsen Goudarzi ◽  
René de Borst ◽  
Taras Gerya ◽  
Meng Li ◽  
van Dinther Ylona
Keyword(s):  
Numerical Model ◽  
Fault Zone ◽  
Induced Seismicity ◽  
Subduction Zones ◽  
Bulk Material ◽  
Fault Zones ◽  
Length Scale ◽  
Internal Length ◽  
Internal Length Scale ◽  
Earthquake Sequences

<p>Accurate representation of fault zones is important in many applications in Earth sciences, including natural and induced seismicity. The framework developed here can efficiently model fault zone localization, evolution, and spontaneous fully dynamic earthquake sequences in a continuum plasticity framework. The geometrical features of the faults are incorporated into a regularized continuum framework, while the response of the fault zone is governed by a rate and state-dependent friction. Although a continuum plasticity model is advantageous to discrete approaches in representing evolving, unknown, or arbitrarily positioned faults, it is known that either non-associated plasticity or strain-softening can lead to mesh sensitivity of the numerical results in absence of an internal length scale. A common way to regularize the numerical model and introduce an internal length scale is by the adoption of a Kelvin-type visco-plasticity element. The visco-plastic rheological behavior for the bulk material is implemented along with a return-mapping algorithm for accurate stress and strain evolution. High slip rates (in the order of 1 m/s) are captured through numerical examples of a predefined strike-slip fault zone, where a detailed comparison with a reference discrete fault model is presented. Additionally, the regularization effect of the Kelvin viscosity parameter is studied on the fault slip velocity for a growing fault zone due to an initial material imperfection.  The model is consistently linearized leading to quadratic convergence of the Newton solver. Although the proposed framework is a step towards the modeling of earthquake sequences for induced seismicity applications, the numerical model is general and can be applied to all tectonic settings including subduction zones.</p><div> <div> <div> </div> <div> <div> <div> </div> <div> <p> </p> <p> </p> </div> </div> </div> </div> </div>

On the impact of alternative seismic time imaging methods on subsurface fault mapping in the northernmost Molasse Basin, Switzerland

2020 ◽  
Vol 8 (4) ◽  
pp. SQ1-SQ13
Author(s):  
Christoph G. Eichkitz ◽  
Sarah Schneider ◽  
Andreas B. Hölker ◽  
Philip Birkhäuser ◽  
Herfried Madritsch
Keyword(s):  
Fault Zone ◽  
Three Dimensions ◽  
Small Scale ◽  
Zone Model ◽  
Molasse Basin ◽  
Data Set ◽  
Volume Comparison ◽  
Imaging Methods ◽  
Seismic Amplitude ◽  
The Impact

The identification and characterization of tectonic faults in the subsurface represent key aspects of geologic exploration activities across the world. We have evaluated the impact of alternative seismic time imaging methods on initial subsurface fault mapping in three dimensions in the form of a case study situated in the most external foreland of the European Central Alps (the northernmost Molasse Basin). Four different seismic amplitude volumes of one and the same 3D seismic data set, differing in imaging technologies and parameterizations applied, were considered for the interpretation of a fault zone dissecting a Mesozoic sedimentary sequence that is characterized by a pronounced mechanical stratigraphy and has witnessed a multiphase tectonic evolution. For this purpose, we interpreted each seismic amplitude volume separately. In addition, we computed a series of seismic attributes individually for each volume. Comparison of the different data interpretations revealed consistent results concerning the mapping of the seismic marker horizons and main fault segments. Deviations concern the apparent degree of vertical and lateral fault zone segmentation and the occurrence of small-scale fault strands that may be regarded as important fault kinematic indicators. The compilation of all fault interpretations in map form allows the critical assessment of the robustness of the initial seismic fault mapping, highlighting well-constrained from poorly defined fault zone elements. We conclude that the consideration of multiple seismic processing products for subsurface fault mapping is advisable to evaluate general imaging uncertainties and potentially guide the development of fault zone model variants to tackle previously discussed aspects of conceptual interpretation uncertainties.

Fine Structure of the Chenghai Fault Zone, Yunnan, China, Constrained From Teleseismic Travel Time and Ambient Noise Tomography

2020 ◽  
Vol 125 (7) ◽  
Author(s):  
Hongfeng Yang ◽  
Yaohui Duan ◽  
Junhao Song ◽  
Xiaohuan Jiang ◽  
Xiaofeng Tian ◽  
...  
Keyword(s):  
Fine Structure ◽  
Travel Time ◽  
Fault Zone ◽  
Ambient Noise ◽  
Ambient Noise Tomography

Estimating Intersection Control Delay Using Large Data Sets of Travel Time from a Global Positioning System

2005 ◽  
Vol 1917 (1) ◽  
pp. 18-27
Author(s):  
Brian Hoeschen ◽  
Darcy Bullock ◽  
Mark Schlappi
Keyword(s):  
Travel Time ◽  
Traffic Engineering ◽  
Large Data ◽  
Large Data Sets ◽  
Data Sets ◽  
Data Set ◽  
Control Delay ◽  
Diverse Data ◽  
Intersection Control ◽  
Better Than

Historically, stopped delay was used to characterize the operation of intersection movements because it was relatively easy to measure. During the past decade, the traffic engineering community has moved away from using stopped delay and now uses control delay. That measurement is more precise but quite difficult to extract from large data sets if strict definitions are used to derive the data. This paper evaluates two procedures for estimating control delay. The first is based on a historical approximation that control delay is 30% larger than stopped delay. The second is new and based on segment delay. The procedures are applied to a diverse data set collected in Phoenix, Arizona, and compared with control delay calculated by using the formal definition. The new approximation was observed to be better than the historical stopped delay procedure; it provided an accurate prediction of control delay. Because it is an approximation, this methodology would be most appropriately applied to large data sets collected from travel time studies for ranking and prioritizing intersections for further analysis.

Tracking earthquake sequences in real time: application of Seismicity-Scanning based on Navigated Automatic Phase-picking (S-SNAP) to the 2019 Ridgecrest, California sequence

2020 ◽  
Vol 223 (3) ◽  
pp. 1511-1524
Author(s):  
Fengzhou Tan ◽  
Honn Kao ◽  
Edwin Nissen ◽  
Ryan Visser
Keyword(s):  
Real Time ◽  
Fault Zone ◽  
Southern California ◽  
Main Shock ◽  
Waveform Data ◽  
Major Earthquake ◽  
Automatic Phase ◽  
Seismicity Monitoring ◽  
Earthquake Sequences ◽  
Automatic Phase Picking

SUMMARY Recent improvements in seismic data processing techniques have enhanced our ability to detail the evolution of major earthquake sequences in space and time. One such advance is new scanning algorithms that allow large volumes of waveform data to be analysed automatically, removing human biases and inefficiencies that inhibit standardized monitoring. The Seismicity-Scanning based on Navigated Automatic Phase-picking (S-SNAP) workflow has previously been shown to be capable of producing high-quality earthquake catalogues for injection-induced seismicity monitoring. In this study, we modify the original S-SNAP workflow to enable it to delineate the spatiotemporal distribution of major earthquake sequences in real time. We apply it to the 2019 Ridgecrest, southern California earthquake sequence, which culminated in an Mw 6.4 foreshock on July 4 and an Mw 7.1 main shock on July 6 and generated tens of thousands of smaller earthquakes. Our catalogue—which spans the period 2019 June 1 to July 16—details the spatiotemporal evolution of the sequence, including early foreshocks on July 1 and accelerating foreshocks on July 4, a seismicity gap before the main shock around its epicentre, seismicity on discrete structures within a broad fault zone and triggered earthquakes outside the main fault zone. We estimate the accuracy and false detection rate of the S-SNAP catalogue based on the reviewed catalogue reported by Southern California Seismic Network (SCSN) and our own visual inspection. We demonstrate the advantages of S-SNAP over a generalized automatic earthquake monitoring software, Seiscomp3, and a customized real-time earthquake information system for southern California, TriNet. In comparison, the S-SNAP catalogue contains five times more events than the Seiscomp3 catalogue and 1.4–2.2 times as many events per hour as the TriNet catalogue at most times. In addition, S-SNAP is more likely to solve phase association ambiguities correctly and provide a catalogue with consistent quality through time. S-SNAP would be beneficial to both routine network operations and the earthquake review process.

Point-process models with linearly parametrized intensity for application to earthquake data

1986 ◽  
Vol 23 (A) ◽  
pp. 291-310 ◽  
Author(s):  
Yosihiko Ogata ◽  
Koichi Katsura
Keyword(s):  
Seismic Activity ◽  
Process Models ◽  
Evolutionary Trend ◽  
Conditional Intensity ◽  
Data Set ◽  
Technical Aspects ◽  
Point Process Models ◽  
Earthquake Sequences ◽  
Flexible Models ◽  
Earthquake Data

It is demonstrated that linear parametrization of the conditional intensity provides systematic classes of flexible models which are reasonably useful for calculating maximum likelihoods. To exemplify the modelling, seismic activity around Canberra is decomposed into components of evolutionary trend, clustering and periodicity. The causal relationship between earthquake sequences from two seismic regions is also analysed for a certain Japanese earthquake data set.Some technical aspects of the modelling and calculations are described.

scholarly journals Travel-Time Inversion Method of Converted Shear Waves Using RayInvr Algorithm

2021 ◽  
Vol 11 (8) ◽  
pp. 3571
Author(s):  
Genggeng Wen ◽  
Kuiyuan Wan ◽  
Shaohong Xia ◽  
Huilong Xu ◽  
Chaoyan Fan ◽  
...  
Keyword(s):  
Travel Time ◽  
Wave Velocity ◽  
P Wave ◽  
Inversion Method ◽  
Time Inversion ◽  
Ocean Bottom Seismometer ◽  
S Wave ◽  
S Waves ◽  
Inversion Model ◽  
Travel Time Inversion

The detailed studies of converted S-waves recorded on the Ocean Bottom Seismometer (OBS) can provide evidence for constraining lithology and geophysical properties. However, the research of converted S-waves remains a weakness, especially the S-waves’ inversion. In this study, we applied a travel-time inversion method of converted S-waves to obtain the crustal S-wave velocity along the profile NS5. The velocities of the crust are determined by the following four aspects: (1) modelling the P-wave velocity, (2) constrained sediments Vp/Vs ratios and S-wave velocity using PPS phases, (3) the correction of PSS phases’ travel-time, and (4) appropriate parameters and initial model are selected for inversion. Our results show that the vs. and Vp/Vs of the crust are 3.0–4.4 km/s and 1.71–1.80, respectively. The inversion model has a similar trend in velocity and Vp/Vs ratios with the forward model, due to a small difference with ∆Vs of 0.1 km/s and ∆Vp/Vs of 0.03 between two models. In addition, the high-resolution inversion model has revealed many details of the crustal structures, including magma conduits, which further supports our method as feasible.

Detection of repeating earthquakes in the West Bohemia swarm region

2020 ◽  
Author(s):  
Ali Salama ◽  
Tomas Fischer
Keyword(s):  
Fault Zone ◽  
Seismic Velocity ◽  
Background Activity ◽  
Source Parameters ◽  
The West ◽  
Data Set ◽  
Repeating Earthquakes ◽  
Waveform Cross Correlation ◽  
Cross Correlation Analysis ◽  
West Bohemia

<p> </p><p><span><strong> </strong></span></p><p> </p><p><span>Repeating earthquakes, sequences of microseismic events with highly similar seismograms and magnitudes, suggest quasi-periodic rupturing of the same asperity. They are observed on creeping fault segments surrounded by aseismic slip area and also in earthquake swarms. However, so far, they have not been documented in the West Bohemia/Vogtland seismic swarm area. These local swarms consist of thousands of M</span><sub><span>L</span></sub><span> < 4 events occurring along a small area of fault zone with repeated activation of some patches during the swarms and weak background activity in the intermediate periods. Detecting and analyzing the repeating earthquakes would help revealing the continuing background activity and identifying fault areas that are active permanently. This could point to the possible sources of fluids or aseismic creep that are supposed to play significant role in swarm generation. Repeating earthquakes are identified by waveform cross-correlation analysis comparing waveforms of repeaters with continuous seismic data set. We developed efficient detection algorithm to identify repeating earthquakes using selected event templates to reveal continuing seismic activity along the main Nový Kostel fault zone, namely in the areas with only episodic activity. The results provide a robust basis for routine application to the long-term seismic dataset that will allow also for further applications including analysis of the source parameters of the repeaters and/or detecting possible seismic velocity variations in the focal zone. </span></p><p> </p>

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