The 1995 off-Etorofu earthquake: Joint relocation of foreshocks, the mainshock, and aftershocks and implications for the earthquake nucleation process

1998 ◽  
Vol 88 (5) ◽  
pp. 1112-1126
Author(s):  
Nobuo Hurukawa
Keyword(s):  
Source Area ◽  
Large Earthquake ◽  
Nucleation Process ◽  
Final Size ◽  
Weak Zone ◽  
Hypocenter Determination ◽  
The North ◽  
Joint Hypocenter Determination ◽  
Kurile Islands ◽  
Foreshock Activity

Abstract Prominent foreshock activity preceded the Mw 7.9 off-Etorofu earthquake in the Kurile Islands on 3 December 1995. Using a modified joint hypocenter determination method (Hurukawa, 1995), we simultaneously relocated foreshocks, the mainshock, and aftershocks to study the foreshock activity in detail in view of the nucleation process of a large earthquake. The distribution of relocated earthquakes and their focal mechanisms suggest that the 1995 off-Etorofu earthquake was an interplate earthquake at the boundary between the North American and Pacific plates. Its source area overlaps with those of the 1958 off-Etorofu (Mw 8.3) and the 1963 off-Urup (Mw 8.5) earthquakes. Nine days before the occurrence of the mainshock, a first immediate foreshock of magnitude 6.4 occurred at the deepest point of the foreshock area. This event was followed by many foreshocks, including three additional M ≧ 6 events, which occurred east and southeast of the first foreshock. The foreshock area expanded toward the trench axis with a velocity of several to several tens centimeters per second. The number of events per day increased daily, and the final size of the foreshock area was about 80 × 30 km. Eventually, the rupture of the mainshock started at the deepest point of the foreshock area. These observational facts are consistent with recent theoretical studies and laboratory experiments, in which foreshocks are regarded as the rupture of localized asperities in a broad weak zone where the nucleation of the large earthquake started.

scholarly journals Fractal Approach: Quantification of Seismicity in South Central Tibet

BIBECHANA ◽  
1970 ◽  
Vol 8 ◽  
pp. 116-126
Author(s):  
Harihar Paudyal ◽  
PNS Roy
Keyword(s):  
Correlation Dimension ◽  
Large Earthquake ◽  
Weak Zone ◽  
Entire Study ◽  
Fractal Approach ◽  
The North ◽  
South Central ◽  
Stressed Region ◽  
Central Tibet ◽  
Clustering Pattern

The South Central Tibet (SCT) region is inferred to be an extensional regime since it is predominantly associated with normal faulting with E-W oriented horizontal tension axis representing extension in eastwest direction. In this paper the fractal analysis is carried out using the seismicity data (mb≥3.5) for last 47 years (1963-2009) in SCT to the north of Central Himalaya. The entire study area is bounded by 29o-31o N and 85o-90o E. The study escorted to the recognition of a clustering events in two consecutive fifty events window having low spatial fractal correlation dimension (Dc) value ranging from 0.3638 to 0.5451 during the period between 07.26.1998 to 03.23.2002. Relatively two lower Dc obtained prior to strong event. Spatial-temporal clustering of events during low Dc period actually specifies a highly stressed region, leading to increase of shear strain causing weak zone from where the rupture propagation may ultimately nucleate causing large earthquake. This type of clustering pattern study using the well constrained catalogue data for the SCT region, which has a record of high seismic activity for the entire last two decades, can assist to enhance the understanding and mitigation of earthquake hazard.Keywords: Fractal spatial; correlation dimension (Dc); clustering; seismicityDOI: http://dx.doi.org/10.3126/bibechana.v8i0.5699  BIBECHANA 8 (2012) 116-126

Migratory Labour from North-Wester Nigeria

Africa ◽  
1957 ◽  
Vol 27 (3) ◽  
pp. 251-261 ◽  
Author(s):  
R. Mansell Prothero
Keyword(s):  
Large Scale ◽  
Source Area ◽  
Dry Season ◽  
Labour Migration ◽  
Agricultural Activity ◽  
Wet Season ◽  
The North ◽  
The People ◽  
Limited Scale ◽  
Opening Paragraph

Opening ParagraphReaders of Africa will be well aware of population migration as a characteristic feature of a continent where movement between one part and another is largely unrestricted as compared with the more settled parts of the world. There is much evidence of large-scale tribal migrations in the past, of the age-old seasonal wanderings of herders, and of recent labour migration to centres of mineral and industrial production, the last particularly in Central and South Africa. Information is more limited concerning the features of labour migration in West Africa at the present day. In general it is thought that migrants leave their home areas, after the harvest at the commencement of the dry season, to seek work elsewhere for a period of from three to six months and then return to take up farming with the commencement of the next rains. The major source area for these migrants is to the north of the tenth parallel where the wet season is concentrated into a period of about four months, thus severely restricting agricultural activity. Cultivation during the dry season is possible only on a very limited scale. There is thus a considerable period of the year when the primary economic activity of the people is not possible. It is logical that they should seek work elsewhere.

scholarly journals A missing link in the peri-Gondwanan terrane collage: the Precambrian basement of the Moroccan Meseta and its lower Paleozoic cover

2018 ◽  
Vol 55 (1) ◽  
pp. 33-51 ◽  
Author(s):  
Dominik Letsch ◽  
Mohamed El Houicha ◽  
Albrecht von Quadt ◽  
Wilfried Winkler
Keyword(s):  
Carbonate Platform ◽  
Source Area ◽  
Source Rocks ◽  
Lower Paleozoic ◽  
Northern Margin ◽  
Precambrian Geology ◽  
The North ◽  
Late Cambrian ◽  
Paleozoic Rocks ◽  
Rifted Margin

This article provides stratigraphic and geochronological data from a central part of Gondwana’s northern margin — the Moroccan Meseta Domain. This region, located to the north of the Anti-Atlas area with extensive outcrops of Precambrian and lower Paleozoic rocks, has hitherto not received much attention with regard to its Precambrian geology. Detrital and volcanic zircon ages have been used to constrain sedimentary depositional ages and crustal affinities of sedimentary source rocks in stratigraphic key sections. Based on this, a four-step paleotectonic evolution of the Meseta Domain from the Ediacaran until the Early Ordovician is proposed. This evolution documents the transition from a terrestrial volcanic setting during the Ediacaran to a short-lived carbonate platform setting during the early Cambrian. The latter then evolved into a rifted margin with deposition of thick siliciclastic successions in graben structures during the middle to late Cambrian. The detritus in these basins was of local origin, and a contribution from a broader source area (encompassing parts of the West African Craton) can only be demonstrated for postrifting, i.e., laterally extensive sandstone bodies that seal the former graben. In a broader paleotectonic context, it is suggested that this Cambrian rifting is linked to the opening of the Rheic Ocean, and that several peri-Gondwanan terranes (Meguma and Cadomia–Iberia) may have been close to the Meseta Domain before drifting, albeit some of them seem to have been constituted by a distinctly different basement.

3D Fault Structure Inferred from a Refined Aftershock Catalog for the 2015 Gorkha Earthquake in Nepal

2019 ◽  
Vol 110 (1) ◽  
pp. 26-37 ◽  
Author(s):  
Masumi Yamada ◽  
Thakur Kandel ◽  
Koji Tamaribuchi ◽  
Abhijit Ghosh
Keyword(s):  
Velocity Structure ◽  
Complex Geometry ◽  
Slip Surface ◽  
Hanging Wall ◽  
Velocity Model ◽  
P Wave ◽  
Gorkha Earthquake ◽  
Hypocenter Determination ◽  
The North ◽  
2015 Gorkha Earthquake

ABSTRACT In this article, we created a well-resolved aftershock catalog for the 2015 Gorkha earthquake in Nepal by processing 11 months of continuous data using an automatic onset and hypocenter determination procedure. Aftershocks were detected by the NAMASTE temporary seismic network that is densely distributed covering the rupture area and became fully operational about 50 days after the mainshock. The catalog was refined using a joint hypocenter determination technique and an optimal 1D velocity model with station correction factors determined simultaneously. We found around 15,000 aftershocks with the magnitude of completeness of ML 2. Our catalog shows that there are two large aftershock clusters along the north side of the Gorkha–Pokhara anticlinorium and smaller shallow aftershock clusters in the south. The patterns of aftershock distribution in the northern and southern clusters reflect the complex geometry of the Main Himalayan thrust. The aftershocks are located both on the slip surface and through the entire hanging wall. The 1D velocity structure obtained from this study is almost constant at a P-wave velocity (VP) of 6.0  km/s for a depth of 0–20 km, similar to VP of the shallow continental crust.

scholarly journals Convergence of the Pamir and the South Tian Shan in the late Cenozoic: Insights from provenance analysis in the Wuheshalu section at the convergence area

Lithosphere ◽  
2019 ◽  
Vol 11 (4) ◽  
pp. 507-523 ◽  
Author(s):  
Xinwei Chen ◽  
Hanlin Chen ◽  
Edward R. Sobel ◽  
Xiubin Lin ◽  
Xiaogan Cheng ◽  
...  
Keyword(s):  
Source Area ◽  
Limited Area ◽  
Late Cenozoic ◽  
Provenance Analysis ◽  
The South ◽  
Active Deformation ◽  
The North ◽  
Large Populations ◽  
A Minor ◽  
Tian Shan

Abstract In response to collision and convergence between India and Asia during the Cenozoic, convergence took place between the Pamir and South Tian Shan. Here we present new detrital zircon U-Pb ages coupled with conglomerate clast counting and sedimentary data from the late Cenozoic Wuheshalu section in the convergence zone, to shed light on the convergence process of the Pamir and South Tian Shan. Large Triassic zircon U-Pb age populations in all seven samples suggest that Triassic igneous rocks from the North Pamir were the major source area for the late Cenozoic Wuheshalu section. In the Miocene, large populations of the North Pamir component supports rapid exhumation in the North Pamir and suggest that topography already existed there since the early Miocene. Exhumation of the South Tian Shan was relatively less important in the Miocene and its detritus could only reach a limited area in the foreland area. Gradually increasing sediment loading and convergence of the Pamir and South Tian Shan caused rapid subsidence in the convergence area. Since ca. 6–5.3 Ma, the combination of a major North Pamir component and a minor South Tian Shan component at the Wuheshalu section is consistent with active deformation of the South Tian Shan and the North Pamir. During deposition of the upper Atushi Formation, a larger proportion of North Pamir–derived sediments was deposited in the Wuheshalu section, maybe because faulting and northward propagation of the North Pamir caused northward displacement of the depocenter to north of the Wuheshalu section.

THE DEPOSITIONAL HISTORY OF A PORTION OF THE NORTH PERTH BASIN—A SINGLE WELL DIPMETER ANALYSIS

1971 ◽  
Vol 11 (1) ◽  
pp. 90
Author(s):  
K. J. Bird ◽  
W. F. Coleman ◽  
H. Crocker
Keyword(s):  
First Generation ◽  
Source Area ◽  
Lower Triassic ◽  
Flood Plain ◽  
Upper Jurassic ◽  
Lower Jurassic ◽  
Depositional History ◽  
The North ◽  
Single Well ◽  
History Of

Four-arm dipmeter interpretation has been integrated with other wireline logs, lithologic and palaeontologic data, and regional geology to arrive at a history of the deposition in a portion of the North Perth Basin.The Permian sediments were deposited in a moderate to low energy, paralic to marine environment. They were unconformably overlain by a thin transgressive Lower Triassic sand and deepwater marine shale. The Middle Triassic sediments were deposited as a regressive marine sequence under the influence of a strong southwesterly uplift, and culminated in piedmont talus deposits of Upper Triassic age.In the Lower Jurassic this area evolved through a flood-plain environment to a paralic environment with a northeast-southwest oriented coastline and a northern source area. During the Middle Jurassic gentle crustal movements, coupled with an increasingly active northern and eastern source area, resulted in several cycles of nearshore deposition, and finally a marine transgression.Subsequent violent tectonic uplift to the east in the Upper Jurassic produced massive first generation sands which were deposited in a mainly continental environment.

Sign in / Sign up

Export Citation Format

Share Document