scholarly journals Statistical Distribution of the Difference in Magnitude between the Main Shock and its Largest Aftershock

1979 ◽  
Vol 32 (4) ◽  
pp. 463-476 ◽  
Author(s):  
Masami OKADA
Keyword(s):  
Main Shock ◽  
Statistical Distribution ◽  
The Difference ◽  
Largest Aftershock

Spatial distribution of the difference between the magnitudes of the main shock and the largest aftershock in the circum-Pacific belt

1990 ◽  
Vol 80 (5) ◽  
pp. 1180-1189
Author(s):  
Theodoros M. Tsapanos
Keyword(s):  
Spatial Distribution ◽  
Main Shock ◽  
Plate Boundaries ◽  
Plate Interface ◽  
The Difference ◽  
Back Arc ◽  
Earthquake Sequences ◽  
Largest Aftershock ◽  
Magnitude Difference ◽  
Good Number

Abstract The distribution of the magnitude difference D1 between the main shock and the largest aftershock for large circum-Pacific earthquakes is observed to be peaked at 1.2 magnitude units, in accord with Bath's law, but also at 1.8 magnitude units. The peak at 1.8 has been not noted before and is shown here with the T-test to be statistically valid. The observed spatial distribution of the sequences is the basis to suggest that, along circum-Pacific convergent plate boundaries, values of D1, tend to be larger for earthquake sequences within back-arc areas as compared to sequences closer to the plate interface, although admittedly a good number of exceptions to this generalization are also observed to exist.

Stress drop and aftershocks

1973 ◽  
Vol 63 (4) ◽  
pp. 1433-1446
Author(s):  
S. J. Gibowicz
Keyword(s):  
Stress Drop ◽  
Main Shock ◽  
Local Magnitude ◽  
Principal Characteristics ◽  
Fault Surface ◽  
A Value ◽  
High Magnitude ◽  
Aftershock Sequences ◽  
The Difference ◽  
Largest Aftershock

abstract Eighteen aftershock sequences, nine from California and nine from New Zealand, are studied. It is found that a general relationship exists between the local magnitude ML and the stress drop in the main shock. The stress drop in the main earthquake determines the principal characteristics of the aftershock sequences. A low stress drop leads to a low value of the coefficient b, high magnitude of the largest aftershock, and short duration, and conversely. A sequence is arbitrarily considered to be over when the rate of aftershock occurrence falls to a value of one shock per day. The duration depends on the area of fault surface and the stress drop in the main shock. For an average stress drop, the coefficient b has a value of 0.8 to 0.9, and the difference in magnitude between the main shock and the largest aftershock is 1.2, a relation often called Båth's law.

Observations of the Coyote Lake, California earthquake sequence of August 6, 1979

1980 ◽  
Vol 70 (2) ◽  
pp. 559-570 ◽  
Author(s):  
R. A. Uhrhammer
Keyword(s):  
San Francisco ◽  
Fault Zone ◽  
Strong Earthquake ◽  
Main Shock ◽  
B Value ◽  
Aftershock Sequence ◽  
The South ◽  
The North ◽  
Temporal And Spatial Characteristics ◽  
Largest Aftershock

abstract At 1705 UTC on August 6, 1979, a strong earthquake (ML = 5.9) occurred along the Calaveras fault zone south of Coyote Lake about 110 km southeast of San Francisco. This strong earthquake had an aftershock sequence of 31 events (2.4 ≦ ML ≦ 4.4) during August 1979. No foreshocks (ML ≧ 1.5) were observed in the 3 months prior to the main shock. The local magnitude (ML = 5.9) and the seismic moment (Mo = 6 × 1024 dyne-cm from the SH pulse) for the main shock were determined from the 100 × torsion and 3-component ultra-long period seismographs located at Berkeley. Local magnitudes are determined for the aftershocks from the maximum trace amplitudes on the Wood-Anderson torsion seismograms recorded at Berkeley (Δ ≊ 110 km). Temporal and spatial characteristics of the aftershock sequence are presented and discussed. Some key observations are: (1) the first six aftershocks (ML ≧ 2.4) proceed along the fault zone progressively to the south of the main shock; (2) all of the aftershocks (ML ≧ 2.4) to the south of the largest aftershock (ML = 4.4) have a different focal mechanism than the aftershocks to the north; (3) no aftershocks (ML ≧ 2.4) were observed significantly to the north of the main shock for the first 5 days of the sequence; and (4) the b-value (0.70 ± 0.17) for the aftershock sequence is not significantly different from the average b-value (0.88 ± 0.08) calculated for the Calaveras fault zone from 16 yr of data.

Common features of the reservoir-associated seismic activities

1972 ◽  
Vol 62 (2) ◽  
pp. 481-492 ◽  
Author(s):  
Harsh K. Gupta ◽  
B. K. Rastogi ◽  
Hari Narain
Keyword(s):  
Main Shock ◽  
Detailed Examination ◽  
Factors Affecting ◽  
B Values ◽  
Common Features ◽  
Rate Of Increase ◽  
Tremor Frequency ◽  
Earthquake Sequences ◽  
Largest Aftershock ◽  
Frequency Magnitude

abstract A detailed examination of the behavior of earthquakes associated with over a dozen artificial lakes shows that, in all cases, the tremors were initiated or their frequency increased considerably following the lake filling and that their epicenters were mostly located within a distance of 25 km from the lakes. Among the factors affecting the tremor frequency are the rate of increase of water level, duration of loading, maximum levels reached, and the period for which the high levels are retained. The study of these reservoir-associated earthquake sequences reveals that the ratio of the largest aftershock to the main shock is high (about 0.9), and the b values are also high in the frequency-magnitude relation, which is contrary to the normal earthquakes of the concerned regions.

The earthquake sequence in Friuli, Italy, 1976

1979 ◽  
Vol 69 (6) ◽  
pp. 1797-1818
Author(s):  
Vittorio Cagnetti ◽  
Vincenzo Pasquale
Keyword(s):  
Main Shock ◽  
Eastern Alps ◽  
Earthquake Sequence ◽  
Laboratory Studies ◽  
Fault Movement ◽  
Stress Changes ◽  
Entire Sequence ◽  
Strain Release ◽  
Largest Aftershock ◽  
Aftershock Region

abstract The seismic activity of the May 6, 1976 Friuli earthquake has been investigated. It provides clear evidence of internal clustering of shocks, with the largest aftershocks being followed by their own series of aftershocks. Late large aftershocks with their own aftershock series occurred 4 months after the main shock, when aftershocks had subsided. Thus, in the entire series of aftershocks, six phases of strain release are found, and part of the aftershock region is not included in the aftershock volume of the main shock. All this indicates that a few aftershocks are at least partially independent from the main shock. The value of b is estimated for the entire sequence and for the separate phases; during the activity, b shows an increase after the main shock, a decline immediately before the largest aftershock, and a second increase immediately afterward. This can be explained in terms of stress changes, and is consistent with laboratory studies of rock deformation. The compressive stress is perpendicular to the Eastern Alps, and may be considered as the principal cause of the earthquake sequence. The solution of the main shock of the sequence is a reversed fault movement, unlike most of the mechanisms in the focus of the earlier Friuli earthquakes which are of the transcurrent type.

scholarly journals Felt reports and impact of the November 25, 1988, magnitude 5.9 Saguenay, Quebec, earthquake sequence

2021 ◽  
Author(s):  
M Lamontagne ◽  
K B S Burke ◽  
L Olson
Keyword(s):  
United States ◽  
20Th Century ◽  
Main Shock ◽  
The United States ◽  
Moment Magnitude ◽  
Earthquake Sequence ◽  
Mass Movements ◽  
Additional Material ◽  
Largest Aftershock ◽  
The Impact

The November 25, 1988, moment magnitude 5.9 (Mw) Saguenay earthquake is one of the largest eastern Canadian earthquakes of the 20th century. It was preceded by a magnitude (MN) 4.7 foreshock and followed by very few aftershocks considering the magnitude of the main shock. The largest aftershock was a magnitude (MN) 4.3 event. This Open File (OF) Report presents a variety of documents (including original and interpreted felt information, images, newspaper clippings, various engineering reports on the damage, mass movements). This OF updates the report of Cajka and Drysdale (1994) with additional material, including descriptions of the foreshock and largest aftershock. Most of the felt report information come from replies of a questionnaire sent to postmasters in more than 2000 localities in Canada and in the United States. Images of the original felt reports from Canada are included. The OF also includes information gathered in damage assessments and newspaper accounts. For each locality, the interpreted information is presented in a digital table. The fields include the name, latitude and longitude of the municipality and the interpreted intensity on the Modified Mercalli Intensity (MMI) scale (most of which are the interpretations of Cajka and Drysdale, 1996). When available or significant, excerpts of the felt reports are added. This OF Report also includes images from contemporary newspapers that describe the impact. In addition, information contained in post-earthquake reports are discussed together with pictures of damage and mass movements. Finally, a GoogleEarth kmz file is added for viewing the felt information reports within a spatial tool.

Earthquake frequency and prediction

1984 ◽  
Vol 74 (1) ◽  
pp. 255-265
Author(s):  
Zheng-rong Liu
Keyword(s):  
Earthquake Prediction ◽  
Main Shock ◽  
Republic Of China ◽  
Daily Count ◽  
Aftershock Sequences ◽  
Earthquake Frequency ◽  
Prediction Technique ◽  
Largest Aftershock

Abstract The coefficient p in n(t) = n1t−p, where n(t) is the daily count of earthquakes and n1 is the number of earthquakes on the first day following a larger earthquake, is ≦1 for foreshock sequences, ≳1 for double-main shock sequences, and »1 for aftershock sequences with a single largest earthquake. For p »1, the magnitude of the largest aftershock and the cutoff time of the aftershocks can be estimated. These observations are the basis for an earthquake prediction technique successfully used in the Peoples Republic of China (PRC).

The Broach earthquake of March 23, 1970

1972 ◽  
Vol 62 (1) ◽  
pp. 47-61
Author(s):  
Harsh K. Gupta ◽  
Indra Mohan ◽  
Hari Narain
Keyword(s):  
Main Shock ◽  
Fault Plane ◽  
Geological Structure ◽  
P Wave ◽  
Field Observations ◽  
B Values ◽  
Macroseismic Effects ◽  
Godavari Valley ◽  
First Motion ◽  
Largest Aftershock

Abstract The recent seismicity of the Broach region has been studied and correlated with the regional geological structure. The macroseismic effects are briefly described. Analysis of the first motion of P-wave data indicates the plane striking N 92°E to be the fault plane as supported by field observations also. The present seismic activity is found to be similar to the recent Godavari Valley earthquake sequence of April 1970 and different from the earthquakes in the Koyna region on the basis of b values, foreshock-aftershock pattern, and the ratio of the largest aftershock to the main shock magnitude.

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