Single-station fault plane solutions

1982 ◽  
Vol 72 (3) ◽  
pp. 729-744
Author(s):  
Charles A. Langston
Keyword(s):  
Fault Plane ◽  
Fault Plane Solutions ◽  
Waveform Data ◽  
Motion Study ◽  
Single Station ◽  
Source Mechanisms ◽  
First Motion ◽  
Motion Studies ◽  
Using Data ◽  
Pattern Information

abstract Fault plane solutions are derived from systematic trial-and-error (“grid”) testing of three-component body waveform data from a single station. Modeling P and SH waveform data from five shallow events recorded teleseismically demonstrates that radiation pattern information contained within the interference of the direct wave and surface reflections and the overall relative amplitude between P and SH waveforms is sufficient to discriminate between fault type (e.g., strike-slip versus dip-slip) and often agrees with well-constrained first-motion studies. Events studied are the 9 April 1968 Borrego Mountain, California; 20 June 1978 Thessaloniki, Greece; 13 August 1978 Santa Barbara, California; 20 May 1979 Alaska; and 6 August 1979 Coyote Lake, California, earthquakes. It is also shown using data from the 27 July 1980 Sharpsburg, Kentucky, earthquake that inclusion of pP/P and sP/P polarity and amplitude information to an otherwise unconstrained first-motion study can significantly improve the quality of the fault plane solution. Although there are many potential problems (source multiplicity, directivity, etc.) which can prohibit finding a good model with these techniques and inclusion of data from many stations is clearly desirable, the results of this study suggest that sparse, high-quality waveform data sets may be as or more useful for obtaining source mechanisms than standard first-motion studies. At a minimum, they should be performed together as a consistency check. This procedure would be most useful in the common situation where only a few receivers are available for a particular event.

Detection of possible seismic station phase reversals using parametric data from seismological bulletins

2021 ◽  
Author(s):  
Konstantinos Lentas
Keyword(s):  
Goodness Of Fit ◽  
Seismic Station ◽  
Waveform Data ◽  
Seismic Stations ◽  
Velocity Models ◽  
Parametric Data ◽  
Source Mechanisms ◽  
First Motion ◽  
Earthquake Mechanism ◽  
Using Data

<p>A simple and fast technique to detect systematic changes in the performance of seismic stations by using parametric data is being presented. The methodology is based on a simple principal, notably, quantifying the goodness of fit of first motion manually picked polarities from seismological bulletins versus available earthquake mechanism solutions over time. The probability of the reporting polarity data fitting (and not fitting) source mechanisms is quantified by calculating the probability distribution of several Bernoulli trials over a randomly perturbed set of hypocentres and velocity models for each earthquake mechanism - station polarity combination. The method was applied to the registered seismic stations in the bulletin of the International Seismological Centre (ISC) after grouping each polarity pick by reporting agency, using data from the past two decades. The overall agreement of first motion polarities against source mechanisms is found to be good with a few cases of seismic stations showing indications of systematic phase reversals over certain time periods. Specifically, results were obtained for 50% of the registered stations at the ISC, and from these stations 70% show reliable operation during the operational time period under investigation, with only 3% showing the opposite, and 7% showing evidence of systematic changes in the quality of the reported first motion polarities. The rest showed great variability over short periods of time, which does not allow one to draw any conclusions. Comparing waveform data with the associated reported polarities revealed a mixture of cases of either questionable picking or true station phase reversals.</p>

scholarly journals A holistic seismotectonic model of Delhi region

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Brijesh K. Bansal ◽  
Kapil Mohan ◽  
Mithila Verma ◽  
Anup K. Sutar
Keyword(s):  
Strain Energy ◽  
Fault Plane ◽  
Near Field ◽  
Energy Estimates ◽  
The West ◽  
Fault Plane Solutions ◽  
Northern India ◽  
Structural Environment ◽  
Reverse Faulting ◽  
Using Data

AbstractDelhi region in northern India experiences frequent shaking due to both far-field and near-field earthquakes from the Himalayan and local sources, respectively. The recent M3.5 and M3.4 earthquakes of 12th April 2020 and 10th May 2020 respectively in northeast Delhi and M4.4 earthquake of 29th May 2020 near Rohtak (~ 50 km west of Delhi), followed by more than a dozen aftershocks, created panic in this densely populated habitat. The past seismic history and the current activity emphasize the need to revisit the subsurface structural setting and its association with the seismicity of the region. Fault plane solutions are determined using data collected from a dense network in Delhi region. The strain energy released in the last two decades is also estimated to understand the subsurface structural environment. Based on fault plane solutions, together with information obtained from strain energy estimates and the available geophysical and geological studies, it is inferred that the Delhi region is sitting on two contrasting structural environments: reverse faulting in the west and normal faulting in the east, separated by the NE-SW trending Delhi Hardwar Ridge/Mahendragarh-Dehradun Fault (DHR-MDF). The WNW-ESE trending Delhi Sargoda Ridge (DSR), which intersects DHR-MDF in the west, is inferred as a thrust fault. The transfer of stress from the interaction zone of DHR-MDF and DSR to nearby smaller faults could further contribute to the scattered shallow seismicity in Delhi region.

Analysis of Shallow Microearthquakes in the South Sebec Seismic Zone, Maine, 1989–1990

1992 ◽  
Vol 63 (4) ◽  
pp. 557-566 ◽  
Author(s):  
William E. Doll ◽  
Carol D. Rea ◽  
John E. Ebel ◽  
Sandra J. Craven ◽  
John J. Cipar
Keyword(s):  
New England ◽  
Satellite Images ◽  
Fault Plane ◽  
Seismic Zone ◽  
Fault Plane Solutions ◽  
Motion Data ◽  
First Motion ◽  
High Level ◽  
Surface Geology

Abstract Fifteen years of regional monitoring by the New England Seismic Network indicated a locally high level of seismicity near South Sebec, between the towns of Milo and Dover-Foxcroft in central Maine. Most of the events were located in a diffuse zone south of the distinctive, ENE trending Harriman Pond Fault (HPF) which is indicated by brittle deformation in outcrop and is represented as a depression in topographic maps and satellite images. A portable network consisting of both digital and analog instruments was deployed during the summers of 1989 and 1990 in order to characterize the pattern of the microearthquakes and to determine high-resolution epicenters, depths, and fault plane solutions. Seventy-three events were detected during the experiment, of which 28 could be located. Many of the events south of the fault lie along a NNW trending line which has no major expression in the surface geology. Only, a few of the events are subparallel to the HPF. The first motion data were insufficient for the determination of any fault plane solutions.

scholarly journals Relocation of clustered earthquakes in the Groningen gas field

2017 ◽  
Vol 96 (5) ◽  
pp. s163-s173 ◽  
Author(s):  
Lisanne Jagt ◽  
Elmer Ruigrok ◽  
Hanneke Paulssen
Keyword(s):  
S Wave ◽  
Gas Field ◽  
Single Station ◽  
Source Mechanisms ◽  
The Difference ◽  
Multiplet Analysis ◽  
Using Data ◽  
Groningen Gas Field ◽  
Master Event ◽  
Improved Accuracy

AbstractPrevious locations of earthquakes induced by depletion of the Groningen gas field were not accurate enough to infer which faults in the reservoir are reactivated. A multiplet analysis is performed to identify clusters of earthquakes that have similar waveforms, representing repeating rupture on the same or nearby faults. The multiplet analysis is based on the cross-correlation of seismograms to assess the degree of similarity. Using data of a single station, six earthquake clusters within the limits of the Groningen field were identified for the period 2010 to mid-2014. Four of these clusters were suitable for a relocation method that is based on the difference in travel time between the P- and the S-wave. Events within a cluster can be relocated relative to a master event with improved accuracy by cross-correlating first arrivals. By choosing master events located with a new dense seismic network, the relocated events likely not only have better relative, but also improved absolute locations. For a few clusters with sufficient signal-to-noise detections, we show that the relocation method is successful in assigning clusters to specific faults at the reservoir level. Overall, about 90% of the events did not show clustering, despite choosing low correlation thresholds of 0.5 and 0.6. This suggests that different faults and/or fault segments with likely varying source mechanisms are active in reservoir sub-regions of a few square kilometres.

scholarly journals The ISC Bulletin as a comprehensive source of earthquake source mechanisms

2019 ◽  
Vol 11 (2) ◽  
pp. 565-578 ◽  
Author(s):  
Konstantinos Lentas ◽  
Domenico Di Giacomo ◽  
James Harris ◽  
Dmitry A. Storchak
Keyword(s):  
Earthquake Source ◽  
Current Status ◽  
Fault Plane Solutions ◽  
Double Couple ◽  
Source Mechanisms ◽  
Best Fitting ◽  
First Motion ◽  
International Seismological Centre ◽  
Different Sources ◽  
Major Data

Abstract. In this article we summarize the availability of earthquake source mechanisms in the Bulletin of the International Seismological Centre (ISC). The bulletin in its current status contains ∼81 000 seismic events with only one associated mechanism solution and ∼25 000 events with at least two associated source mechanisms. The main sources of earthquake mechanisms in the ISC Bulletin are reported solutions provided by data contributors and ISC-computed focal mechanisms based on first motion polarities. Given the importance of using pre-determined fault plane solutions in different types of studies, here we briefly discuss the methodologies adopted by major data providers to the ISC and investigate the intra-event variability of the source mechanisms. We conclude that the overall agreement among different earthquake mechanisms for the same event as reported by different sources can show a similarity coefficient as high as 80 %, based on the rotation angles of their best-fitting double couple solutions, for the majority of the cases. The earthquake source mechanisms discussed in this work are freely available within the ISC Bulletin websearch at http://doi.org/10.31905/D808B830.

scholarly journals The ISC Bulletin as a comprehensive source of earthquake source mechanisms

2018 ◽  
Author(s):  
Konstantinos Lentas ◽  
Domenico Di Giacomo ◽  
James Harris ◽  
Dmitry Storchak
Keyword(s):  
Focal Mechanisms ◽  
Earthquake Source ◽  
Current Status ◽  
Fault Plane Solutions ◽  
Different Types ◽  
Source Mechanisms ◽  
First Motion ◽  
International Seismological Centre ◽  
Different Sources ◽  
Major Data

Abstract. In this article we summarize the availability of earthquake source mechanisms in the Bulletin of the International Seismological Centre (ISC). The bulletin in its current status contains ∼ 81,000 seismic events with only one associated mechanism solution, and ∼ 22,000 events with at least two associated source mechanisms. The main sources of earthquake mechanisms in the ISC Bulletin are reported solutions provided by data contributors, and ISC computed focal mechanisms based on first motion polarities. Given the importance of using pre-determined fault plane solutions in different types of studies, here we focus only on the reported mechanisms and we briefly discuss the methodologies adopted by major data providers to the ISC and investigate the intra-event variability of the source mechanisms. We conclude that the overall agreement among different earthquake focal mechanisms for the same event as reported by different sources can be as high as 90% for the majority of the cases. The earthquake source mechanisms discussed in this work are freely available within the ISC Bulletin websearch at http://doi.org/10.31905/D808B830.

The earthquake sequence of November 1964 near Corralitos, California

1966 ◽  
Vol 56 (3) ◽  
pp. 755-773 ◽  
Author(s):  
Thomas V. McEvilly
Keyword(s):  
Fault Plane ◽  
San Andreas Fault ◽  
Focal Region ◽  
Fault Plane Solutions ◽  
Central California ◽  
San Andreas ◽  
Motion Characteristic ◽  
First Motion ◽  
The Times ◽  
The Right

abstract A sequence of more than 100 aftershocks with magnitudes as low as −0.1 was recorded following a magnitude 5.0 earthquake on November 16, 1964, in the San Andreas fault zone of central California. The sequence was monitored in detail by three temporary seismographic stations at distances less than 15 km and the surrounding telemetry array. Nearly all of the 35 earthquakes which could be located clustered in a focal region about 4 km in diameter at a depth near 12 km and exhibited uniform first motion radiation patterns. First motion fault plane solutions are consistent with the right lateral transcurrent motion characteristic of the San Andreas fault. Exceptions to this uniform radiation pattern in the concentrated focal region occurred near the times of two large aftershocks apparently on another fault about 5 km away.

The geometrical representation of fault-plane solutions of earthquakes

1957 ◽  
Vol 47 (2) ◽  
pp. 89-110 ◽  
Author(s):  
Adrian E. Scheidegger
Keyword(s):  
Mathematical Model ◽  
North America ◽  
Infinite Number ◽  
Fault Plane ◽  
Stereographic Projection ◽  
Fault Plane Solutions ◽  
Plausible Assumption ◽  
Long Time ◽  
First Motion ◽  
The Mathematical Model

Abstract Investigations into the mechanism at the focus of an earthquake have been in progress for a long time. In the course of these investigations it has been demonstrated that the mathematical model of a simple fault is a plausible assumption, at least so far as the explanation of the direction of first motion at distant seismic observatories is concerned. Various methods have been devised for representing and determining the elements of the focal fault of an earthquake, by investigators in Japan, Holland, North America, Italy, and Russia. It is often very difficult to see the connection between the various representations, and the present paper has been undertaken to demonstrate the relationships between them and to devise corresponding “translation schemes.” It is shown that there exists an infinite number of representations of fault-plane solutions all of which satisfy certain basic requirements. However, only four thereof have reached any popularity. It is shown that three of these four representations are entirely equivalent. In each, one uses a sphere; in each, one uses some stereographic projection of this sphere; and in each, one substitutes the tangent to the seismic ray at the focus for the ray itself. Whether one tabulates the angle i which that tangent makes with the vertical and plots tan i/2, as Ritsema and most Russians do, or whether one tabulates and plots tan i, as some of the Russians do, or tabulates and plots cot i, as Hodgson and his various co-workers do, one obtains identical results with equivalent amounts of work. What particular representation anyone will choose for studying an earthquake will therefore depend largely on his taste and previous custom.

Three Kamchatka earthquakes

1960 ◽  
Vol 50 (3) ◽  
pp. 347-388
Author(s):  
William Stauder
Keyword(s):  
Fault Plane ◽  
Focal Depth ◽  
Analytical Techniques ◽  
Aftershock Sequence ◽  
Great Earthquake ◽  
S Wave ◽  
Fault Plane Solutions ◽  
S Waves ◽  
Double Couple ◽  
First Motion

ABSTRACT Three earthquakes, two with previously determined fault-plane solutions, are selected in order to study the relation between the S waves and the source mechanism. The S waves are observed at favorable epicentral distances at stations distributed in all quadrants about the epicenter. The earthquakes are of a focal depth of 40 to 60 kilometers and belong to the aftershock sequence of the great earthquake of November 4, 1952. The direction of first motion and the plane of polarization of S are determined by the construction of particle-motion diagrams. In the case of the two earthquakes for which the fault-plane solutions have been published, no correspondence is found between the observed S wave data and the character of the S motion expected on the basis of the given nodal planes of P, whether the source be considered as a single couple or as a double couple. For the third earthquake it is found that the first motion of P is compressional along all rays leaving the focus downward and that the S waves are strongly SV polarized. No faulting mechanism can explain this distribution of the motion in the initial P and S phases. The motion is explained as corresponding to that generated by a simple force acting almost vertically downward. Graphical and analytical techniques of analysis determine the trend of the force at the source to be N 12° W, with a plunge of 85°. A reconsideration of the other two shocks shows that these, too, are better explained by a simple force source than by a faulting mechanism.

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