Elastic displacements in the near-field of a propagating fault

1969 ◽  
Vol 59 (2) ◽  
pp. 865-908
Author(s):  
N. A. Haskell
Keyword(s):  
Fault Plane ◽  
Near Field ◽  
Strong Motion ◽  
Dislocation Motion ◽  
Displacement Discontinuity ◽  
Wave Form ◽  
Strong Motion Station ◽  
Ramp Function ◽  
Wave Forms ◽  
Parkfield Earthquake

abstract Displacement, particle velocity, and acceleration wave forms in the near field of a propagating fault have been computed by numerical integration of the Green's function integrals for an infinite medium. The displacement discontinuity (dislocation) on the fault plane is assumed to have the form of a unilaterally propagating finite ramp function in time. The calculated wave forms in the vicinity of the fault plane are quite similar to those observed at the strong motion station nearest the fault plane at the Parkfield earthquake. The comparison suggests that the propagating ramp time function is roughly representative of the main features of the dislocation motion on the fault plane, but that the actual motion has somewhat more high frequency complexity. Calculated amplitudes indicate that the average final dislocation on the fault at the Parkfield earthquake was more than an order of magnitude greater than the offsets observed on the visible surface trace. Computer generated wave form plots are presented for a variety of locations with respect to the fault plane and for two different assumptions on the relation between fault length and ramp function duration.

Elastodynamic near-field of a finite, propagating tensile fault

1972 ◽  
Vol 62 (3) ◽  
pp. 675-697 ◽  
Author(s):  
N. A. Haskell ◽  
K. C. Thomson
Keyword(s):  
Numerical Integration ◽  
Particle Velocity ◽  
Fault Plane ◽  
Near Field ◽  
Infinite Medium ◽  
Displacement Discontinuity ◽  
Wave Form ◽  
Acceleration Wave ◽  
Ramp Function ◽  
Wave Forms

Abstract Displacement, particle velocity, and acceleration wave forms in the near-field of a finite, propagating tensile fault have been computed by numerical integration of the Green's function integrals for an infinite medium. The displacement discontinuity (dislocation) on the fault plane is assumed to have the form of a unilaterally propagating, finite ramp function in time. Computer generated wave-form plots are presented for a variety of close-in locations with respect to the fault plane and for two different fault lengths.

Control of rupture by fault geometry during the 1966 parkfield earthquake

1981 ◽  
Vol 71 (1) ◽  
pp. 95-116 ◽  
Author(s):  
Allan G. Lindh ◽  
David M. Boore
Keyword(s):  
Main Shock ◽  
Fault Plane ◽  
San Andreas Fault ◽  
Strong Motion ◽  
P Wave ◽  
Fault Geometry ◽  
Dynamic Rupture ◽  
San Andreas ◽  
Hill Station ◽  
Parkfield Earthquake

abstract A reanalysis of the available data for the 1966 Parkfield, California, earthquake (ML=512) suggests that although the ground breakage and aftershocks extended about 40 km along the San Andreas Fault, the initial dynamic rupture was only 20 to 25 km in length. The foreshocks and the point of initiation of the main event locate at a small bend in the mapped trace of the fault. Detailed analysis of the P-wave first motions from these events at the Gold Hill station, 20 km southeast, indicates that the bend in the fault extends to depth and apparently represents a physical discontinuity on the fault plane. Other evidence suggests that this discontinuity plays an important part in the recurrence of similar magnitude 5 to 6 earthquakes at Parkfield. Analysis of the strong-motion records suggests that the rupture stopped at another discontinuity in the fault plane, an en-echelon offset near Gold Hill that lies at the boundary on the San Andreas Fault between the zone of aseismic slip and the locked zone on which the great 1857 earthquake occurred. Foreshocks to the 1857 earthquake occurred in this area (Sieh, 1978), and the epicenter of the main shock may have coincided with the offset zone. If it did, a detailed study of the geological and geophysical character of the region might be rewarding in terms of understanding how and why great earthquakes initiate where they do.

scholarly journals The February 9, 1971 San Fernando earthquake: A study of source finiteness in teleseismic body waves

1978 ◽  
Vol 68 (1) ◽  
pp. 1-29 ◽  
Author(s):  
Charles A. Langston
Keyword(s):  
Near Field ◽  
Dislocation Line ◽  
Strong Motion ◽  
Body Waves ◽  
P Waves ◽  
Long Period ◽  
Short Period ◽  
Wave Forms ◽  
San Fernando ◽  
The Time Domain

abstract Teleseismic P, SV, and SH waves recorded by the WWSS and Canadian networks from the 1971 San Fernando, California earthquake (ML = 6.6) are modeled in the time domain to determine detailed features of the source as a prelude to studying the near and local field strong-motion observations. Synthetic seismograms are computed from the model of a propagating finite dislocation line source embedded in layered elastic media. The effects of source geometry and directivity are shown to be important features of the long-period observations. The most dramatic feature of the model is the requirement that the fault, which initially ruptured at a depth of 13 km as determined from pP-P times, continuously propagated toward the free surface, first on a plane dipping 53°NE, then broke over to a 29°NE dipping fault segment. This effect is clearly shown in the azimuthal variation of both long period P- and SH-wave forms. Although attenuation and interference with radiation from the remainder of the fault are possible complications, comparison of long- and short-period P and short-period pP and P waves suggest that rupture was initially bilateral, or, possibly, strongly unilateral downward, propagating to about 15 km depth. The average rupture velocity of 1.8 km/sec is well constrained from the shape of the long-period wave forms. Total seismic moment is 0.86 × 1026 dyne-cm. Implications for near-field modeling are drawn from these results.

scholarly journals Parkfield earthquake of June 28, 1966: Magnitude and source mechanism

1968 ◽  
Vol 58 (2) ◽  
pp. 689-709
Author(s):  
Francis T. Wu
Keyword(s):  
Love Wave ◽  
Main Shock ◽  
Near Field ◽  
Strong Motion ◽  
Wave Radiation ◽  
Motion Data ◽  
Long Period ◽  
Short Period ◽  
Double Couple ◽  
Parkfield Earthquake

Abstract The Parkfield earthquake of June 28, 1966 (04:26:12.4 GMT) is studied using short-period and long-period teleseismic records. It is found that (1) Mb = 5.8 and Ms = 6.4 as compared to Mb = 5.4 and Ms = 5.4 for the foreshock (04:08:54), (2) both the Rayleigh and Love wave radiation patterns conform to those of a double couple at a depth of about 8.6 km, (3) the main shock can be represented by a series of shocks separated in space and time. The near-field strong-motion data support the last conclusion. Based on strong-motion seismograms, and the surficial evidences of the dimensions of the fault, the energy is found to be 1021 ergs.

Focal mechanism determination and identification of the fault plane of earthquakes using only one or two near-source seismic recordings

1999 ◽  
Vol 89 (6) ◽  
pp. 1558-1574 ◽  
Author(s):  
Bertrand Delouis ◽  
Denis Legrand
Keyword(s):  
Focal Mechanism ◽  
Fault Plane ◽  
Epicentral Distance ◽  
Near Field ◽  
Waveform Inversion ◽  
Strong Motion ◽  
Source Model ◽  
Resolving Power ◽  
Fault Parameters ◽  
Single Station

Abstract A waveform inversion scheme was developed in order to explore the resolving power of one or two seismic recordings at short epicentral distance for the determination of focal mechanisms and the identification of the fault plane of earthquakes. Two key features are used to constrain the fault parameters with a reduced number of stations: (1) a simple finite-dimension source model and (2) the modeling of the complete displacement field, including the near-field waves. The identification of the fault plane should be possible, even with a single station, as soon as the seismograms produced by the two nodal planes of a same focal mechanism are significantly different, which is the general case when waveforms are controlled by source finiteness. Seven parameters, including the strike, dip, rake, and dislocation, are explored with a grid search, and the minima of the misfit error between the observed and calculated seismograms are mapped. With such an approach, it is possible to conclude about the uniqueness or nonuniqueness of the solutions. The method is tested with three earthquakes of moderate to large size for which the fault plane is well established and for which strong-motion records are available at maximum distances of a few tens of kilometers. Test events are the 1994 Northridge (Mw = 6.7, California), the 1996 Copala (Mw = 7.3, Mexico), and the 1996 Pinotepa Nacional (Mw = 5.4, Mexico) earthquakes. In the case of inversions with two stations, we find a unique solution, or a group of similar solutions, with a good estimation of the focal mechanism and the proper selection of the fault plane. Our results also show that in some cases a single station may be enough to recover the fault parameters. The inversion scheme presented here may be systematically applied to future earthquakes, especially to those recorded by few stations. It should be particularly useful in the case of blind faults for which the fault plane may not be identified with the help of other data.

Automatic Extraction of Permanent Ground Offset from Near-Field Accelerograms: Algorithm, Validation, and Application to the 2004 Parkfield Earthquake

2020 ◽  
Vol 110 (6) ◽  
pp. 2638-2646
Author(s):  
Asaf Inbal ◽  
Alon Ziv
Keyword(s):  
Near Field ◽  
Strong Motion ◽  
Fault Slip ◽  
Global Navigation Satellite Systems ◽  
New Approach ◽  
Satellite Systems ◽  
Spatial Coverage ◽  
Parkfield Earthquake ◽  
Seismic Moment Release ◽  
Global Navigation Satellite

ABSTRACT Permanent ground offsets, constituting a prime dataset for constraining final fault-slip distributions, may not be recovered straightforwardly by double integration of near-field accelerograms due to tilt and other distorting effects. Clearly, if a way could be found to recover permanent ground offsets from acceleration records, then static datasets would be enlarged, and thus the resolution of fault-slip inversions would be enhanced. Here, we introduce a new approach for extracting permanent offsets from near-field strong-motion accelerograms. The main advantage of the new approach with respect to previous ones is that it corrects for source time functions of any level of complexity. Its main novelty is the addition of a constraint on the slope of the ground velocity spectra at long periods. We validated the new scheme using collocated accelerograms and Global Navigation Satellite Systems (GNSS) records of the 2011 Mw 9 Tohoku-Oki earthquake. We find a good agreement between accelerogram-based and GNSS-based ground offsets over a range of 0.1–5 m. To improve the spatial coverage of permanent ground offsets associated with the 2004 Parkfield earthquake, near-field accelerograms were baseline corrected using the new scheme. Static slip inversion of the combined GNSS-based and accelerogram-based ground displacements indicates appreciable seismic moment release south of the epicenter, about 5 km into the Cholame section of the San Andreas fault. We conclude that the strong shaking observed to the south of the epicenter is directly related to the slip in that area and is not the result of local amplification.

Rupture process of the 1980 Izu-Hanto-Toho-Oki earthquake deduced from strong motion seismograms

1988 ◽  
Vol 78 (3) ◽  
pp. 1074-1091
Author(s):  
Minoru Takeo
Keyword(s):  
Seismic Moment ◽  
Fault Plane ◽  
Near Field ◽  
Source Region ◽  
Vertical Plane ◽  
Strong Motion ◽  
Rupture Process ◽  
Japan Meteorological Agency ◽  
Inversion Method ◽  
Total Seismic Moment

Abstract The 1980 Izu-Hanto-Toho-Oki earthquake is studied in detail using near-field strong motion seismograms recorded at Japan Meteorological Agency stations. A seismogram inversion method is applied to deduce the dislocation distribution and the character of rupture propagation during this earthquake. This earthquake involves left-lateral strike-slip motion on the almost vertical plane with a strike of N10°W. The fault plane is shallower than about 12 km in depth, and the length is about 20 km. The large dislocation (large seismic moment) occurs near the hypocenter and at the southern end of the fault plane. The rupture propagates southward from the central part of the fault plane and spreads to the shallow area of the northern part of the fault plane after a delay of about 5 sec relative to the initiation of this earthquake. The total seismic moment is about 7 ×1025 dyne·cm. The aftershocks of magnitude equal to or greater than 4.0 take place in the areas where high stresses are expected to remain after this earthquake. The mechanical weakness of small submarine monogenetic volcanoes which are located above the source region seems to affect the rupture process of this earthquake.

scholarly journals Faulting process of the San Fernando earthquake of February 9, 1971 inferred from static and dynamic near-field displacements

1973 ◽  
Vol 63 (1) ◽  
pp. 249-269 ◽  
Author(s):  
Takeshi Mikumo
Keyword(s):  
Fault Plane ◽  
Ground Motions ◽  
Near Field ◽  
Ground Surface ◽  
Thrust Faulting ◽  
Theoretical Predictions ◽  
Wave Forms ◽  
San Fernando ◽  
North And South ◽  
Horizontal Displacements

abstract The faulting process of the San Fernando earthquake of February 9, 1971 has been investigated using the following seismic and geodetic data: vertical and horizontal displacements, strain and tilt changes, dynamic ground motions in the near-field, focal mechanism, spatial distribution of aftershocks and features of surface fault breaks. A synthetic study suggests that the earthquake was caused by thrust faulting with a slip of 233° to 244° over a fault plane with dimensions 19 by 14 km, dip 50° to 52° and strike N64° to 70°W, which ruptures the ground surface over a distance of about 12 km. The fracture initiating at the hypocenter of the main shock seems to have propagated radially over the fault plane with a velocity about 2.5 km/sec. A small dislocation less than 30 cm at initiation probably increased rapidly during propagation and reached 3.5 to 4 m at the ground surface. A pronounced uplift and small subsidence of the ground north and south of the fault traces, and the overall pattern of the observed vertical and horizontal displacements can be explained well by the above model, but the recorded strain and tilt offsets are not always consistent with theoretical predictions. The wave forms and amplitudes for some of the integrated ground displacements from accelerograms at the Pacoima Dam and Pasadena are in fairly close agreement with those of the computed displacements. The seismic moment and stress drop of this earthquake were found to be 1.1 × 1026 dyne·cm and 40 to 65 bars, respectively.

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.

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