scholarly journals The aftershock sequence of the north-west Kashmir earthquake of September 3, 1972

2010 ◽  
Vol 28 (2-3) ◽  
Author(s):  
V. K. SRIVASTAVA ◽  
R. K. S. CHOUHAN ◽  
R. NIGAM
Keyword(s):  
Upper Mantle ◽  
B Value ◽  
Aftershock Sequence ◽  
Creep Recovery ◽  
Average Strain ◽  
Shear Creep ◽  
Kashmir Earthquake ◽  
North West ◽  
The North ◽  
Total Average

This paper is an attempt to study the aftershock sequence of the Northwest Kashmir earthquake of September 3, 1972. b value of the sequence is 1.59. The area of active strain zone is approximately 2.9 • ]013 sq. cm. The total average strain, average elastic energy and average stress of the rock before slip are 3.3 • 10~5, 3.2 ergs/cm3 and 19.8 kg/cm2. The strain rebound curve of the sequence has been constructed which shows a dual type of recovery where the compressional elastic creep is followed by the shear creep recovery. The relaxation time of the sequence is about 0.7 day, showing the Kelvin body like behaviour of the upper mantle.

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.

scholarly journals The 1991 Sierra Madre earthquake sequence in southern California: Seismological and tectonic analysis

1994 ◽  
Vol 84 (4) ◽  
pp. 1058-1074 ◽  
Author(s):  
Egill Hauksson
Keyword(s):  
Los Angeles ◽  
Fault Plane ◽  
B Value ◽  
Tectonic Stress ◽  
Aftershock Sequence ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Stress Axis ◽  
The North ◽  
Sierra Madre

Abstract The (ML 5.8) Sierra Madre earthquake of 28 June 1991 occurred at a depth of 12 km under the San Gabriel Mountains of the central Transverse Ranges. Since at least 1932 this region had been quiescent for M ≧ 3. The mainshock focal mechanism derived from first-motion polarities exhibited almost pure thrust faulting, with a rake of 82° on a plane striking N62°E and dipping 50° to the north. The event appears to have occurred on the Clamshell-Sawpit fault, a splay of the Sierra Madre fault zone. The aftershock sequence following the mainshock occurred at a depth of 9 to 14 km and was deficient in small earthquakes, having a b value of 0.6. Twenty nine single-event focal mechanisms were determined for aftershocks of M > 1.5. The 4-km-long segment of the Clamshell-Sawpit fault that may have ruptured in the mainshock is outlined by several thrust focal mechanisms with an east-northeast-striking fault plane dipping to the north. To the west, several thrust aftershocks with east-striking nodal planes suggest some complexity in the aftershock faulting, such as a curved rupture surface. In addition, several strike-slip and normal faulting events occurred along the edges of the mainshock fault plane, indicating secondary tear faulting. The tectonic stress field driving the coexisting left-lateral strike-slip and thrust faults in the northern Los Angeles basin is north-south horizontal compression with vertical intermediate or minimum principal stress axis.

Real-time discrimination of earthquake foreshocks and aftershocks

2020 ◽  
Author(s):  
Laura Gulia ◽  
Stefan Wiemer
Keyword(s):  
Real Time ◽  
Large Earthquake ◽  
B Value ◽  
Aftershock Sequence ◽  
Main Question ◽  
Traffic Light ◽  
Background Value ◽  
The North ◽  
The Hours ◽  
Average Size

<p>Immediately after a large earthquake, the main question asked by the public and decision-makers is whether it was the mainshock or a foreshock to an even stronger event yet to come. So far, scientists can only offer empirical evidence from statistical compilations of past sequences, arguing that normally the aftershock sequence will decay gradually whereas the occurrence of a forthcoming larger event has a probability of a few per cent.</p><p>We analyse the average size distribution of aftershocks of the 2016 Amatrice–Norcia (Italy) and Kumamoto (Japan) earthquake sequences and we suggest that in many cases it may be possible to discriminate whether an ongoing sequence represents a decaying aftershock sequence or foreshocks to an upcoming large event.</p><p>We propose a simple traffic light classification (FTLS, Foreshock Traffic Light System) to assess in real time the level of concern about a subsequent larger event and test it against 58 sequences, achieving a classification accuracy of 95 per cent.</p><p>We finally test, in near-real-time, the performance of the FTLS to the 2019 Ridgecrest sequence, California: a Mw6.4 followed, about 2 days later, by a Mw7.1. We find that in the hours after the first Ridgecrest event (Mw 6.4, the b-value drops by 23% on average, when compared to the background value, resulting in a ‘red’ foreshock traffic light.</p><p>Mapping in space the changes in b, we identify an area to the north of the rupture plane as the most likely location of a subsequent event. The second mainshock of magnitude 7.1 then indeed occurred in this location and after this event, the b-value increased by 26 percent over the background value, resulting in a green traffic light state.</p>

scholarly journals Role of multifractal analysis in understanding the preparation zone for large size earthquake in the North-Western Himalaya region

2011 ◽  
Vol 18 (1) ◽  
pp. 111-118 ◽  
Author(s):  
S. S. Teotia ◽  
D. Kumar
Keyword(s):  
Western Himalaya ◽  
B Value ◽  
Great Earthquake ◽  
Kashmir Earthquake ◽  
The North ◽  
Large Size ◽  
Time Period ◽  
Spatio Temporal ◽  
Self Organised Criticality ◽  
North Western

Abstract. Seismicity has power law in space, time and magnitude distributions and same is expressed by the fractal dimension D, Omori's exponent p and b-value. The spatio-temporal patterns of epicenters have heterogeneous characteristics. As the crust gets self-organised into critical state, the spatio-temporal clustering of epicenters emerges to heterogeneous nature of seismicity. To understand the heterogeneous characteristics of seismicity in a region, multifractal studies hold promise to characterise the dynamics of region. Multifractal study is done on seismicity data of the North-Western Himalaya region which mainly involve seismogenic region of 1905 Kangra great earthquake in the North-Western Himalaya region. The seismicity data obtained from USGS catalogue for time period 1973–2009 has been analysed for the region which includes the October 2005 Muzafrabad-Kashmir earthquake (Mw =7.6). Significant changes have been observed in generalised dimension Dq, Dq spectra and b-value. The significant temporal changes in generalised dimension Dq, b-value and Dq−q spectra prior to occurrence of Muzaffrabad-Kashmir earthquake relates to distribution of epicenters in the region. The decrease in generalised dimension and b-value observed in our study show the relationship with the clustering of seismicity as is expected in self-organised criticality behaviour of earthquake occurrences. Such study may become important in understanding the preparation zone of large and great size earthquake in various tectonic regions.

Observed Seismic Behavior of Buildings in Northern Pakistan during the 2005 Kashmir Earthquake

2010 ◽  
Vol 26 (2) ◽  
pp. 425-449 ◽  
Author(s):  
Amjad Naseer ◽  
Akhtar Naeem Khan ◽  
Zakir Hussain ◽  
Qaisar Ali
Keyword(s):  
Seismic Behavior ◽  
Lessons Learned ◽  
Masonry Buildings ◽  
Kashmir Earthquake ◽  
North West ◽  
Clay Bricks ◽  
The North ◽  
Concrete Blocks ◽  
2005 Kashmir Earthquake ◽  
Recent Earthquakes

Recent earthquakes in Pakistan demonstrated that the region is highly seismic. Masonry buildings constructed with stones, concrete blocks, and fired-clay bricks and concrete buildings were damaged during the 8 October 2005 Kashmir earthquake. This paper presents the seismic behavior of reinforced concrete and masonry buildings in northern part of the North-West Frontier Province (NWFP) and Kashmir during the earthquake. Most of the buildings were observed to be nonengineered or semi-engineered. The paper presents an overview of the 1937 Quetta building code and the 1986 and 2007 building codes of Pakistan. Lessons learned during the earthquake are also presented.

Application of the Foreshock Traffic Light System to the 2019 Ridgecrest sequence

2021 ◽  
Author(s):  
Laura Gulia ◽  
Stefan Wiemer ◽  
Gianfranco Vannucci
Keyword(s):  
Size Distribution ◽  
Reference Value ◽  
B Value ◽  
Aftershock Sequence ◽  
Traffic Light ◽  
Natural Systems ◽  
Background Value ◽  
Light System ◽  
The North ◽  
Average Size

<p>The relative earthquake size distribution, or b-value of the Gutenberg and Richter relationship, can act as an indirect stress meter in the earth crust, a finding confirmed in numerous laboratory studies but also in diverse natural systems.  In 2018, we analysed the average size-distribution of about 60 well-monitored earthquakes sequences showing that, after a mainshock with M>=6, the b-value increases by about 20% respect to the background reference value.</p><p>In 2019, based on such result, we hypothesized and demonstrated that it may be possible, under specific circumstances, to discriminate if an ongoing sequence is representing a typically decaying aftershock sequence or rather foreshocks to an upcoming larger event.  We proposed a simple traffic light classification to assess in near real-time the level of concern for subsequent larger event, and tested it against 58 sequences, reaching a classification accuracy of 95%.</p><p>The Foreshock Traffic Light System (FTLS) has been implemented in a pseudo-prospective test to the 2019 Ridgecrest sequence. Results are fully in line with the hypothesis: in this Ridgecrest case study, after analyzing carefully the magnitude of completeness of the sequences, we find that in the hours after the first Mw6.4 Ridgecrest event, the b-value drops by 23% on average, when compared to the background value, resulting in a red foreshock traffic light. Spatially mapping the changes in b, we identify an area to the north of the rupture plane as the most likely location of a subsequent event. After the second, magnitude-7.1 mainshock, which did occur in the low b-value region, the b-value subsequently increased by 26% over the background value, triggering a green traffic light setting. Here we will report on these findings, discuss additional case studies, criticisms raised and discuss physics-based mechanics that may allow us to understand and model the observations.</p>

Ground effects from the gnome and logan explosions

1962 ◽  
Vol 52 (5) ◽  
pp. 1047-1056
Author(s):  
D. S. Carder
Keyword(s):  
Upper Mantle ◽  
Seismic Waves ◽  
Strong Motion ◽  
Geodetic Survey ◽  
The West ◽  
North West ◽  
The North ◽  
Plateau Area ◽  
Ground Effects ◽  
Potash Mine

abstract Seismic waves resulting from a low yield nuclear detonation 1200 feet deep in a salt bed near Carlsbad, New Mexico were measured by strong-motion seismographs operated by the Coast and Geodetic Survey on the surface in the distance range from 0.5 to 8.8 miles and underground in a potash mine 8.7 to 11.2 miles distant. In addition, many temporary and permanent seismographs were operated by the Coast and Geodetic Survey and other organizations on a continentwide and a world-wide basis. Ground particle accelerations exceeded those from the Logan shot, a like detonation in tuff, by a factor of about 4, and accelerations underground in the salt bed were about half those on the nearby surface. There was no evidence of damaging accelerations in nearby commercial operations or dwellings. Nearby transient ground particle displacements were about the same as those from the logan shot, except that the frequencies were higher. Attenuation with distance across the plains to the east was relatively low as compared with similar effects in the mountain and plateau area toward the west. Upper mantle velocities likewise were higher toward the east, 8.3 to 8.4 km/sec, as compared with 7.8 to 8.1 km/sec toward the north, west, and northwest. The estimated magnitude of the gnome shot was from 4.5 to 5.0, depending on the choice of data.

SEM and TEM observations of sperm development in the testis of the freshwater fish Oreochromis mossambicus

1990 ◽  
Vol 48 (3) ◽  
pp. 58-59
Author(s):  
Daryl A. Cornish ◽  
George L. Smit
Keyword(s):  
Morphological Characteristics ◽  
Oreochromis Mossambicus ◽  
Breeding Cycle ◽  
Limited Information ◽  
North West ◽  
The North ◽  
Sem And Tem ◽  
Sperm Development ◽  
Ultrastructural Characteristics ◽  
The University

Oreochromis mossambicus is currently receiving much attention as a candidater species for aquaculture programs within Southern Africa. This has stimulated interest in its breeding cycle as well as the morphological characteristics of the gonads. Limited information is available on SEM and TEM observations of the male gonads. It is known that the testis of O. mossambicus is a paired, intra-abdominal structure of the lobular type, although further details of its characteristics are not known. Current investigations have shown that spermatids reach full maturity some two months after the female becomes gravid. Throughout the year, the testes contain spermatids at various stages of development although spermiogenesis appears to be maximal during November when spawning occurs. This paper describes the morphological and ultrastructural characteristics of the testes and spermatids.Specimens of this fish were collected at Syferkuil Dam, 8 km north- west of the University of the North over a twelve month period, sacrificed and the testes excised.

The North West Passage

2014 ◽  
Author(s):  
Roald Amundsen ◽  
Godfred Hansen
Keyword(s):  
North West ◽  
The North
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