The Godavari Valley earthquake sequence of April 1969

1970 ◽  
Vol 60 (2) ◽  
pp. 601-615 ◽  
Author(s):  
Harsh K. Gupta ◽  
Indra Mohan ◽  
Hari Narain
Keyword(s):  
Main Shock ◽  
Focal Depth ◽  
Earthquake Sequence ◽  
Total Strain ◽  
Type I ◽  
Aftershock Area ◽  
Macroseismic Effects ◽  
Godavari Valley

abstract The Godavari Valley earthquake sequence of April 1969 has been studied in detail. The (Sg − Pg) and the (Pg − Pn) intervals have been used for estimating the extent of aftershock area and focal depth variations respectively. The main shock of magnitude 5.7 was followed by a number of aftershocks which are related by the function Log N = a + b M. The value of b is found to be −0.51. The main shock of April 13 accounted for 70 per cent of the total strain released. This sequence belongs to Type I of Mogi's classification. The macroseismic effects are also discussed briefly.

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.

scholarly journals The Zagreb (Croatia) M5.5 Earthquake on 22 March 2020

Geosciences ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 252 ◽  
Author(s):  
Snježana Markušić ◽  
Davor Stanko ◽  
Tvrtko Korbar ◽  
Nikola Belić ◽  
Davorin Penava ◽  
...  
Keyword(s):  
Structural Engineering ◽  
Main Shock ◽  
Residential Buildings ◽  
Tectonic Setting ◽  
Time Lapse ◽  
Earthquake Sequence ◽  
Epicentral Area ◽  
Local Soil ◽  
Seismic Amplification ◽  
Zagreb Area

On 22 March 2020, Zagreb was struck by an M5.5 earthquake that had been expected for more than 100 years and revealed all the failures in the construction of residential buildings in the Croatian capital, especially those built in the first half of the 20th century. Because of that, extensive seismological, geological, geodetic and structural engineering surveys were conducted immediately after the main shock. This study provides descriptions of damage, specifying the building performances and their correlation with the local soil characteristics, i.e., seismic motion amplification. Co-seismic vertical ground displacement was estimated, and the most affected area is identified according to Sentinel-1 interferometric wide-swath data. Finally, preliminary 3D structural modeling of the earthquake sequence was performed, and two major faults were modeled using inverse distance weight (IDW) interpolation of the grouped hypocenters. The first-order assessment of seismic amplification (due to site conditions) in the Zagreb area for the M5.5 earthquake shows that ground motions of approximately 0.16–0.19 g were amplified at least twice. The observed co-seismic deformation (based on Sentinel-1A IW SLC images) implies an approximately 3 cm uplift of the epicentral area that covers approximately 20 km2. Based on the preliminary spatial and temporal analyses of the Zagreb 2020 earthquake sequence, the main shock and the first aftershocks evidently occurred in the subsurface of the Medvednica Mountains along a deep-seated southeast-dipping thrust fault, recognized as the primary (master) fault. The co-seismic rupture propagated along the thrust towards northwest during the first half-hour of the earthquake sequence, which can be clearly seen from the time-lapse visualization. The preliminary results strongly support one of the debated models of the active tectonic setting of the Medvednica Mountains and will contribute to a better assessment of the seismic hazard for the wider Zagreb area.

scholarly journals Application of the Environmental Seismic Intensity scale (ESI 2007) and the European Macroseismic Scale (EMS-98) to the Kalamata (SW Peloponnese, Greece) earthquake (Ms=6.2, September 13, 1986) and correlation with neotectonic structures and active faults

2014 ◽  
Vol 56 (6) ◽  
Author(s):  
Ioannis G. Fountoulis ◽  
Spyridon D. Mavroulis
Keyword(s):  
Structural Damage ◽  
Active Fault ◽  
Main Shock ◽  
Active Faults ◽  
Seismic Hazard Assessment ◽  
Seismic Intensity ◽  
Fault Zones ◽  
Earthquake Sequence ◽  
Ground Subsidence ◽  
Earthquake Scenario

On September 13, 1986, a shallow earthquake (Ms=6.2) struck the city of Kalamata and the surrounding areas (SW Peloponnese, Greece) resulting in 20 fatalities, over 300 injuries, extensive structural damage and many earthquake environmental effects (EEE). The main shock was followed by several aftershocks, the strongest of which occurred two days later (Ms=5.4). The EEE induced by the 1986 Kalamata earthquake sequence include ground subsidence, seismic faults, seismic fractures, rockfalls and hydrological anomalies. The maximum ESI 2007 intensity for the main shock has been evaluated as IX<sub>ESI 2007</sub>, strongly related to the active fault zones and the reactivated faults observed in the area as well as to the intense morphology of the activated Dimiova-Perivolakia graben, which is a 2nd order neotectonic structure located in the SE margin of the Kalamata-Kyparissia mega-graben and bounded by active fault zones. The major structural damage of the main shock was selective and limited to villages founded on the activated Dimiova-Perivolakia graben (IX<sub>EMS-98</sub>) and to the Kalamata city (IX<sub>EMS-98</sub>) and its eastern suburbs (IX<sub>EMS-98</sub>) located at the crossing of the prolongation of two major active fault zones of the affected area. On the contrary, damage of this size was not observed in the surrounding neotectonic structures, which were not activated during this earthquake sequence. It is concluded that both intensity scales fit in with the neotectonic regime of the area. The ESI 2007 scale complemented the EMS-98 seismic intensities and provided a completed picture of the strength and the effects of the September 13, 1986, Kalamata earthquake on the natural and the manmade environment. Moreover, it contributed to a better picture of the earthquake scenario and represents a useful and reliable tool for seismic hazard assessment.

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.

The San Salvador earthquake of May 3, 1965

1966 ◽  
Vol 56 (2) ◽  
pp. 561-575
Author(s):  
Cinna Lomnitz ◽  
Rudolf Schultz
Keyword(s):  
Volcanic Activity ◽  
Main Shock ◽  
Tectonic Setting ◽  
Focal Depth ◽  
Building Codes ◽  
General Area ◽  
Populated Area ◽  
Shallow Subsurface ◽  
San Salvador ◽  
Zoning Regulations

abstract The San Salvador earthquake of May 3, 1965 was preceded by a local seismic swarm of three months duration. The main shock was destructive in a densely populated area of not more than 15 km in radius; the same general area was damaged in the earthquakes of 1576, 1659, 1798, 1839, 1854, 1873, 1880, 1917, and 1919. Over 120 casualties were reported. The epicenter has been located on the south rim of the Median Trough, a post-Pliocene structure which accounts for the high seismic and volcanic activity in the region. The observed intensity is attributable to shallow focal depth and to the presence of thick inhomogeneous beds of fluviatile pumice. The tectonic setting and shallow subsurface factors should be recognized in future building codes and zoning regulations.

Spectral analysis of body waves from the earthquake of February 18, 1956

1964 ◽  
Vol 54 (6A) ◽  
pp. 2017-2035 ◽  
Author(s):  
Tomowo Hirasawa ◽  
William Stauder
Keyword(s):  
Amplitude Ratio ◽  
Source Region ◽  
Focal Depth ◽  
Mean Amplitude ◽  
Theoretical Models ◽  
Body Waves ◽  
P Wave ◽  
Type I ◽  
Type Ii ◽  
S Wave

abstract The earthquake which occurred south of Honshu, Japan, on February 18, 1956 is studied by means of Fourier analysis. The focal depth of the shock is about 450 km and the magnitude is 714 to 712. Three theoretical models of the source mechanism, that is, Type Ia, Type Ib, and Type II, are examined by the observed amplitude spectra of S and ScS waves. It is found that the observed amplitude ratios of the Fourier components between two horizontal components of the S wave and of the ScS wave, respectively, agree well with the theoretical ratios for a Type II source. Under the assumption that spectral structures should be the same at all observing points, the scattering from the mean amplitude is calculated. The result shows that the Type II model is preferable to either of the Type I models. Assuming Honda's volume model, whose radiation pattern corresponds to that of a Type II point source, the radius of the source region is estimated by making use of the amplitude ratio of the Fourier component of the S wave to that of the P wave. The radius of the source is found to be 11 km ± 2 km.

The Denver Earthquake Sequence of March–April 1981

1983 ◽  
Vol 54 (2) ◽  
pp. 3-12
Author(s):  
G. A. Bollinger ◽  
Martha J. Adams ◽  
R. F. Henrisey ◽  
C. J. Langer
Keyword(s):  
Main Shock ◽  
Rocky Mountain ◽  
P Wave ◽  
Earthquake Sequence ◽  
Focal Mechanism Solution ◽  
Multiple Fracture ◽  
Normal Faulting ◽  
Composite Focal Mechanism ◽  
Rocky Mountain Arsenal ◽  
Variable Water

Abstract The Denver earthquake sequence of March–April 1981 was monitored by a network of four permanent and eight portable seismographs. In addition to the main shock (mb = 4.3) on 2 April, six microaftershocks (M < 2) during the subsequent two-week period were recorded and located. Five of those six events had epicenters within the most active area of the 1967–1968 Rocky Mountain Arsenal (RMA) sequence. A composite focal mechanism solution for the main shock and the six aftershocks showed a combination of reverse and strike-slip faulting (14% inconsistency in the 29 P-wave polarities) that is different from the predominantly normal faulting reported for the 1967–1968 RMA sequence. These different focal mechanisms, plus variable water-level response at the RMA well during the earthquake sequence in the 1960’s, may suggest the presence of a multiple fracture system in the source volume.

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