The Sharpsburg, Kentucky, earthquake 27 July 1980: Main shock parameters and isoseismal maps

1982 ◽  
Vol 72 (1) ◽  
pp. 221-236
Author(s):  
Frederick J. Mauk ◽  
Doug Christensen ◽  
Steve Henry
Keyword(s):  
Body Wave ◽  
P Wave ◽  
Eastern United States ◽  
Slip Vector ◽  
Small Component ◽  
Slip Event ◽  
Felt Area ◽  
Body Wave Magnitude ◽  
Epicentral Region ◽  
Average Body

abstract An earthquake having an average body-wave magnitude of 5.1 occurred on Sunday, 27 July 1980 near Sharpsburg, Kentucky. The earthquake was widely felt throughout the Eastern United States and had a maximum Modified Mercalli intensity of VII in the epicentral region. The total felt area was approximately 673,000 km2. The well-constrained focal mechanism based on 128 P-wave first motions combined with other geological and seismological evidence indicates a fault plane striking N42°E, dipping 50°E with a slip vector 184° of the strike. This is a right-lateral strike-slip event with a small component of thrust. Isoseismal data strongly suggest a northeast-directed rupture. The strike is parallel to the trend of the West Hickman Creek fault zone but 30 km to the east of any known faults.

Systematic difference in the ISC body-wave magnitude-seismic moment relationship between intermediate and deep earthquakes

1992 ◽  
Vol 82 (2) ◽  
pp. 819-835
Author(s):  
Keiko Kuge
Keyword(s):  
Seismic Moment ◽  
Body Wave ◽  
Systematic Difference ◽  
P Wave ◽  
Local Structures ◽  
Dependent Relationship ◽  
Deep Earthquakes ◽  
Amplitude Data ◽  
Body Wave Magnitude ◽  
Distance Correction

Abstract There exists a systematic difference in the ISC body-wave magnitude (mbISC) - seismic moment (M0) relationship between intermediate and deep earthquakes around Japan. For earthquakes with the same M0, the mbISC for intermediate events is larger than that for deep events by 0.2 to 0.3 units. The mbISC discrepancy is attributed to the depth-distance correction in the procedure for determining the mbISC; a larger depth-distance correction (≈ 0.2) is made for the intermediate events than the deep events, irrespective of station distance. The discrepancy disappears if no depth-distance correction is made. I observe no depth-dependent relationship between the M0 and the JMA magnitudes (MJMA), which make a different depth-distance correction. No significant depth-dependent mbISC discrepancy appears in other regions; for example, around Tonga, I observe larger ISC P-wave amplitudes from deep events than intermediate events, which could cancel the effect of the depth-distance correction. The depth-dependent mbISC - M0 relationship around Japan is observed irrespective of whether the magnitudes are determined using the amplitude data at far or near stations, or whether stations are used in the dipping direction of the slab or not. The mbISC discrepancy for the same M0 cannot arise from local structures, radiation patterns, and station coverages. This is not attributable to the dataset of the M0 itself because no significant depth-dependent relationship between M0 and MJMA is observed.

The El Asnam, Algeria, earthquake of 10 October 1980: Multiple-source mechanism determined from long-period records

1982 ◽  
Vol 72 (4) ◽  
pp. 1111-1128
Author(s):  
A. Deschamps ◽  
Y. Gaudemer ◽  
A. Cisternas
Keyword(s):  
Main Shock ◽  
Body Wave ◽  
P Wave ◽  
P Waves ◽  
Small Component ◽  
Long Period ◽  
The North ◽  
Complex Source ◽  
Dip Angle ◽  
Good Agreement

abstract We present a study of the El Asnam, Algeria, earthquake of 10 October 1980 from a large collection of long-period surface and body wave records. The focal mechanism of the main shock is well constrained by the P-wave first motions at teleseismic distances and field observations: it was a thrust event on a plane striking N45°E, and a dip angle of 54° to the north. It had a small component of left-lateral motion (λ = 83°) (Ouyed et al., 1981; Gaudemer et al., 1981). This earthquake was very well recorded on WWSSN stations and on GDSN and IDA digital stations, with a good azimuthal distribution. From these records, we confirm the focal solution and obtain a seismic moment Mo = 5 × 1026 dyne-cm. The P-wave seismograms indicate a complex source. We show that it is not sufficient to model the source by a multiple event, but it is also necessary to include a propagation effect in order to explain accurately the waveform. With assumptions based on field observation of the surface breaks, we model the P waves, including two discontinuities of the propagation, along the fault plane and obtain a good agreement of the waveform.

Seismic source functions and magnitude determinations for underground nuclear detonations

1977 ◽  
Vol 67 (1) ◽  
pp. 135-158
Author(s):  
John R. Murphy
Keyword(s):  
Body Wave ◽  
Broad Band ◽  
Seismic Source ◽  
Source Model ◽  
The Body ◽  
P Wave ◽  
Cube Root ◽  
Motion Data ◽  
Surface Wave Data ◽  
Body Wave Magnitude

abstract A variety of near-regional, regional, and teleseismic ground-motion data have been used to evaluate proposed models of the nuclear seismic source function for underground detonations in tuff/rhyolite emplacement media. It has been found that both the near-regional broad-band seismic data and the teleseismic body-wave magnitude data are consistent with the modified source model proposed by Mueller and Murphy (1971) but not with the simple cube-root of the yield-scaling source model. In particular, the observed linearity and slopes of the body-wave magnitude-yield curves as well as the observed variation of P-wave period with yield have been found to be fully compatible with the modified source model. On the other hand, it has been concluded that the observed long-period surface-wave data are inconsistent with a simple, spherically symmetric source model. The results of a preliminary analysis have suggested that this discrepancy may be related to the spall closure phenomenon.

On the relation between modified Mercalli intensity and body-wave magnitude

1979 ◽  
Vol 69 (3) ◽  
pp. 893-909
Author(s):  
Otto W. Nuttli ◽  
G. A. Bollinger ◽  
Donald W. Griffiths
Keyword(s):  
United States ◽  
South Carolina ◽  
San Francisco ◽  
Body Wave ◽  
Strong Motion ◽  
Historical Earthquakes ◽  
P Wave ◽  
Intensity Data ◽  
Lg Wave ◽  
Body Wave Magnitude

abstract This paper is concerned with estimating body-wave magnitude, mb, from the intensity distribution of an earthquake. Initially, it is assumed that modified Mercalli (MM) intensity values are directly related to the (A/T)z values of 1-Hz, Lg-wave ground motion. By comparison with the intensity values of a reference earthquake, magnitudes are calculated for 41 western and central United States earthquakes. Magnitudes of these earthquakes also are determined independently, in the conventional manner, using teleseismic P-wave amplitudes. Comparison of the two sets of magnitude values indicates that the assumed relation between 1-Hz, Lg-wave (A/T)z values and MM intensity does not hold exactly over the mb range of 4.0 to 6.2. An empirical equation is derived to adjust the mb values obtained from intensity data so that they agree with the teleseismic P-wave magnitudes. The method then is applied to estimate mb of some historical earthquakes which occurred prior to 1962. These include the set for which Kanamori and Jennings (1978) estimated ML from strong-motion accelerograms. Some noteworthy United States earthquakes also are considered. These include: the 1811 New Madrid earthquake for which mb is estimated to be 7.3; the 1886 Charleston, South Carolina earthquake, for which mb is estimated to be 6.6 to 6.9; the 1897 Giles County, Virginia earthquake, for which mb is estimated to be 5.8; the 1906 San Francisco, California earthquake, for which mb is estimated to be 6.8 to 7.1. The intensity-attenuation method cannot be used for estimating mb of all historical earthquakes because the intensity data are not always adequate. In some cases, however, the total felt area or the area enclosed by the Modified Mercalli IV isoseism can be determined. It was found that empirical equations relating mb to these areas, which were derived for central and northeastern United States earthquakes, also apply for events in the southeast. These empirical methods are used to estimate mb values for a set of historical Virginia earthquakes.

The 12 July 1986 St. Marys, Ohio Earthquake and Recent Seismicity in the Anna, Ohio Seismogenic Zone

1987 ◽  
Vol 59 (2) ◽  
pp. 57-62 ◽  
Author(s):  
Susan Y. Schwartz ◽  
Douglas H. Christensen
Keyword(s):  
Seismic Behavior ◽  
Body Wave ◽  
Strike Slip ◽  
Seismogenic Zone ◽  
Landsat Images ◽  
Nodal Plane ◽  
Epicentral Area ◽  
Felt Area ◽  
The Town ◽  
Body Wave Magnitude

Abstract An earthquake with body wave magnitude 4.5 occurred in the Anna Ohio Seismogenic Zone near the town of St. Marys, Ohio on 12 July 1986. The St. Marys earthquake had a seismic moment of 4.5 × 1022 dyne-cm and a maximum intensity of VI in the epicentral area. It is the largest event to occur in the Anna, Ohio region since the events of 2 March 1937 (total felt area magnitude=4.7) and 9 March 1937 (total felt area magnitude=4.9). The focal mechanism for the St. Marys earthquake indicates a nearly pure strike-slip motion with one nodal plane approximately parallel to the proposed Anna-Champaign Fault and a nearly horizontal p-axis oriented east-northeast. Although the locations of the 1937 events are not well-determined, reports of maximum intensities for the 1937 events near Anna, Ohio indicate that they occurred in a distinctly different location from the St. Marys earthquake. The seismicity in the Anna Seismogenic Zone indicates that much of the seismic activity is concentrated in a northwest to southeast elongate region, extending from Anna, Ohio northwest past Celina, Ohio. This trend parallels the proposed Anna-Champaign Fault as well as lineaments which can be detected on Landsat images, which suggests that this fault may be controlling the seismic behavior in this region.

The body-wave magnitude mb: an attempt to rationalize the distance-depth correction q(Δ, h)

2020 ◽  
Vol 223 (1) ◽  
pp. 270-288
Author(s):  
Nooshin Saloor ◽  
Emile A Okal
Keyword(s):  
Large Scale ◽  
Body Wave ◽  
Exact Algorithm ◽  
Large Data ◽  
The Body ◽  
P Wave ◽  
Small Scale ◽  
Data Sets ◽  
Data Set ◽  
Body Wave Magnitude

SUMMARY We explore the possible theoretical origin of the distance–depth correction q(Δ, h) introduced 75 yr ago by B. Gutenberg for the computation of the body-wave magnitude mb, and still in use today. We synthesize a large data set of seismograms using a modern model of P-wave velocity and attenuation, and process them through the exact algorithm mandated under present-day seismological practice, to build our own version, qSO, of the correction, and compare it to the original ones, q45 and q56, proposed by B. Gutenberg and C.F. Richter. While we can reproduce some of the large scale variations in their corrections, we cannot understand their small scale details. We discuss a number of possible sources of bias in the data sets used at the time, and suggest the need for a complete revision of existing mb catalogues.

Aftershocks of the February 21, 1973 Point Mugu, California earthquake

1976 ◽  
Vol 66 (6) ◽  
pp. 1931-1952
Author(s):  
Donald J. Stierman ◽  
William L. Ellsworth
Keyword(s):  
Fault Zone ◽  
Main Shock ◽  
Fault Plane ◽  
Body Wave ◽  
P Wave ◽  
Fault System ◽  
Wave Radiation ◽  
Fault Plane Solutions ◽  
Complex Deformation ◽  
Transverse Ranges

abstract The ML 6.0 Point Mugu, California earthquake of February 21, 1973 and its aftershocks occurred within the complex fault system that bounds the southern front of the Transverse Ranges province of southern California. P-wave fault plane solutions for 51 events include reverse, strike slip and normal faulting mechanisms, indicating complex deformation within the 10-km broad fault zone. Hypocenters of 141 aftershocks fail to delineate any single fault plane clearly associated with the main shock rupture. Most aftershocks cluster in a region 5 km in diameter centered 5 km from the main shock hypocenter and well beyond the extent of fault rupture estimated from analysis of body-wave radiation. Strain release within the imbricate fault zone was controlled by slip on preexisting planes of weakness under the influence of a NE-SW compressive stress.

P-wave spectra of nevada test site events at near and very near distances: Implications for a near-regional body wave-surface wave discriminant

1976 ◽  
Vol 66 (3) ◽  
pp. 803-825
Author(s):  
William A. Peppin
Keyword(s):  
Scaling Laws ◽  
Body Wave ◽  
Test Site ◽  
P Wave ◽  
Spectral Amplitude ◽  
Source Spectrum ◽  
Wave Spectra ◽  
Nevada Test Site ◽  
Field Source ◽  
Source Spectra

abstract Some 140 P-wave spectra of explosions, earthquakes, and explosion-induced aftershocks, all within the Nevada Test Site, have been computed from wide-band seismic data at close-in (< 30 km) and near-regional (200 to 300 km) distances. Observed near-regional corner frequencies indicate that source corner frequencies of explosions differ little from those of earthquakes of similar magnitude for 3 < ML < 5. Plots of 0.8 to 1.0 Hz Pg spectral amplitude versus 12-sec Rayleigh-wave amplitude show a linear trend with unit slope over three orders of magnitude for explosions; earthquakes fail to be distinguished from explosions on such a plot. These spectra also indicate similar source spectra for explosions in different media (tuff, alluvium, rhyolite) which corroborates Cherry et al. (1973). Close-in spectra of three large explosions indicate that: (1) source corner frequencies of explosions scale with yield in a way significantly different from previously published scaling laws; (2) explosion source spectra in tuff are flat from 0.2 to 1.0 Hz (no overshoot); (3) the far-field source spectrum decays at least as fast as frequency cubed. Taken together, these data indicate that the following factors are not responsible for Peppin and McEvilly's (1974) near-regional discriminant: (a) source dimension, (b) source rise time, or (c) shape of the source spectrum.

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