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Domingo, 21.10.12

Sismo de 5.3 - 26km ENE de King City, California


San Andreas Fault

The San Andreas Fault forms the main strand of the plate boundary, running from the Gulf of California (Baja California, Mexico) north to the region of Cape Mendocino. The fault in the San Francisco Bay region is a largely strike-slip fault running through the Santa Cruz Mountains, the Gulf of the Farallons west of the Golden Gate, through Tomales Bay and Bodega Bay, and north to Fort Ross and Point Arena. Northward of Point Arena, the location and character of the San Andreas Fault is less well known. The fault in this region is locked, exhibiting no creep at the surface and generating very few microearthquakes that are associated with minor slipping at depth. Through the San Francisco Bay Area, the slip rate on the San Andreas Fault is about 20 mm/yr (4/5 inch/year).

The October 17, 1989 Loma Prieta earthquake was the most recent major earthquake associated with the San Andreas Fault. While the earthquake was not produced by the main San Andreas Fault, it occurred on a closely associated blind thrust fault that had formed as a result of a bend in the San Andreas Fault, south of the bay. Although that earthquake struck along a remote segment of the Santa Cruz Mountains, 64 deaths resulted, most from the collapse of the Cypress Freeway in Oakland. About 16,000 homes and apartment units were uninhabitable after the earthquake. The San Francisco-Oakland Bay Bridge was closed for more than a month because of a collapse of a section of its eastern span.

The left bend in the San Andreas Fault in the Santa Cruz Mountains favors thickening of the crust and uplift of the Earth's surface, and is thought to be responsible to the formation of the Santa Cruz Mountains.

The M7.9 April 18, 1906 San Francisco earthquake was the most recent great earthquake on the San Andreas Fault and it ruptured from approximately Cape Mendocino south to San Juan Bautista. The 1906 earthquake was the largest earthquake to strike Northern California in historic times, and is thought to have killed more than 3,000 Bay Area residents. The epicenter of that earthquake is now estimated to be offshore about 2 miles west of San Francisco. The fire following the 1906 earthquake burned 5 square miles of San Francisco and resulted in 225,000 homeless refuges of the earthquake.

A large (magnitude 6.8) earthquake in 1838 is often assumed to have occurred on the Peninsula segment of the San Andreas Fault. To date, however, unambiguous observations placing that earthquake on the San Andreas Fault have not been found.

The 2003 Working Group for California Earthquake Probability assigned a 21% probability that the San Andreas Fault would produce a magnitude 6.7 or larger earthquake in the next 30 years.


Preferred Location Parameters

ParameterValueUncertainty
Magnitude5.3 MwNot Specified
Location36.311°N, 120.856°W± 0.2 km
Depth9.4 km± 0.5 km
Number of Stations UsedNot Specified
Number of Phases Used81
Minimum Distance7.0 km (0.06°)
Travel Time Residual0.14 sec
Azimuthal Gap68°
Review StatusREVIEWED
Event IDnc71863625


Fonte: USGS

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por Diário de um Bombeiro às 17:54

Sexta-feira, 12.10.12

Sismo de 6.7 a 103km N de Dobo, Indonesia



Seismotectonics of the New Guinea Region and Vicinity

The Australia-Pacific plate boundary is over 4000 km long on the northern margin, from the Sunda (Java) trench in the west to the Solomon Islands in the east. The eastern section is over 2300 km long, extending west from northeast of the Australian continent and the Coral Sea until it intersects the east coast of Papua New Guinea. The boundary is dominated by the general northward subduction of the Australia plate.

Along the South Solomon trench, the Australia plate converges with the Pacific plate at a rate of approximately 95 mm/yr towards the east-northeast. Seismicity along the trench is dominantly related to subduction tectonics and large earthquakes are common: there have been 13 M7.5+ earthquakes recorded since 1900. On April 1, 2007, a M8.1 interplate megathrust earthquake occurred at the western end of the trench, generating a tsunami and killing at least 40 people. This was the third M8.1 megathrust event associated with this subduction zone in the past century; the other two occurred in 1939 and 1977.

Further east at the New Britain trench, the relative motions of several microplates surrounding the Australia-Pacific boundary, including north-south oriented seafloor spreading in the Woodlark Basin south of the Solomon Islands, maintain the general northward subduction of Australia-affiliated lithosphere beneath Pacific-affiliated lithosphere. Most of the large and great earthquakes east of New Guinea are related to this subduction; such earthquakes are particularly concentrated at the cusp of the trench south of New Ireland. 33 M7.5+ earthquakes have been recorded since 1900, including three shallow thrust fault M8.1 events in 1906, 1919, and 2007.

The western end of the Australia-Pacific plate boundary is perhaps the most complex portion of this boundary, extending 2000 km from Indonesia and the Banda Sea to eastern New Guinea. The boundary is dominantly convergent along an arc-continent collision segment spanning the width of New Guinea, but the regions near the edges of the impinging Australia continental margin also include relatively short segments of extensional, strike-slip and convergent deformation. The dominant convergence is accommodated by shortening and uplift across a 250-350 km-wide band of northern New Guinea, as well as by slow southward-verging subduction of the Pacific plate north of New Guinea at the New Guinea trench. Here, the Australia-Pacific plate relative velocity is approximately 110 mm/yr towards the northeast, leading to the 2-8 mm/yr uplift of the New Guinea Highlands.

Whereas the northern band of deformation is relatively diffuse east of the Indonesia-Papua New Guinea border, in western New Guinea there are at least two small (<100,000 km²) blocks of relatively undeformed lithosphere. The westernmost of these is the Birds Head Peninsula microplate in Indonesia's West Papua province, bounded on the south by the Seram trench. The Seram trench was originally interpreted as an extreme bend in the Sunda subduction zone, but is now thought to represent a southward-verging subduction zone between Birds Head and the Banda Sea.

There have been 22 M7.5+ earthquakes recorded in the New Guinea region since 1900. The dominant earthquake mechanisms are thrust and strike slip, associated with the arc-continent collision and the relative motions between numerous local microplates. The largest earthquake in the region was a M8.2 shallow thrust fault event in the northern Papua province of Indonesia that killed 166 people in 1996.

The western portion of the northern Australia plate boundary extends approximately 4800 km from New Guinea to Sumatra and primarily separates Australia from the Eurasia plate, including the Sunda block. This portion is dominantly convergent and includes subduction at the Sunda (Java) trench, and a young arc-continent collision.

In the east, this boundary extends from the Kai Islands to Sumba along the Timor trough, offset from the Sunda trench by 250 km south of Sumba. Contrary to earlier tectonic models in which this trough was interpreted as a subduction feature continuous with the Sunda subduction zone, it is now thought to represent a subsiding deformational feature related to the collision of the Australia plate continental margin and the volcanic arc of the Eurasia plate, initiating in the last 5-8 Myr. Before collision began, the Sunda subduction zone extended eastward to at least the Kai Islands, evidenced by the presence of a northward-dipping zone of seismicity beneath Timor Leste. A more detailed examination of the seismic zone along it's eastern segment reveals a gap in intermediate depth seismicity under Timor and seismic mechanisms that indicate an eastward propagating tear in the descending slab as the negatively buoyant oceanic lithosphere detaches from positively buoyant continental lithosphere. On the surface, GPS measurements indicate that the region around Timor is currently no longer connected to the Eurasia plate, but instead is moving at nearly the same velocity as the Australia plate, another consequence of collision.

Large earthquakes in eastern Indonesia occur frequently but interplate megathrust events related to subduction are rare; this is likely due to the disconnection of the descending oceanic slab from the continental margin. There have been 9 M7.5+ earthquakes recorded from the Kai Islands to Sumba since 1900. The largest was the great Banda Sea earthquake of 1938 (M8.5) an intermediate depth thrust faulting event that did not cause significant loss of life.

TSUNAMI BULLETIN NUMBER 001
PACIFIC TSUNAMI WARNING CENTER/NOAA/NWS
ISSUED AT 0037Z 12 OCT 2012

THIS BULLETIN IS FOR ALL AREAS OF THE INDIAN OCEAN.

... TSUNAMI INFORMATION BULLETIN ...

THIS MESSAGE IS FOR INFORMATION ONLY.

THIS BULLETIN IS ISSUED AS ADVICE TO GOVERNMENT AGENCIES. ONLY
NATIONAL AND LOCAL GOVERNMENT AGENCIES HAVE THE AUTHORITY TO MAKE
DECISIONS REGARDING THE OFFICIAL STATE OF ALERT IN THEIR AREA AND
ANY ACTIONS TO BE TAKEN IN RESPONSE.

AN EARTHQUAKE HAS OCCURRED WITH THESE PRELIMINARY PARAMETERS

ORIGIN TIME - 0032Z 12 OCT 2012
COORDINATES - 5.1 SOUTH 134.1 EAST
LOCATION - ARU ISLANDS REGION INDONESIA
MAGNITUDE - 6.7

EVALUATION

A DESTRUCTIVE WIDESPREAD TSUNAMI THREAT DOES NOT EXIST BASED ON
HISTORICAL EARTHQUAKE AND TSUNAMI DATA.

HOWEVER - THERE IS A VERY SMALL POSSIBILITY OF A LOCAL TSUNAMI
THAT COULD AFFECT COASTS LOCATED USUALLY NO MORE THAN A HUNDRED
KILOMETERS FROM THE EARTHQUAKE EPICENTER. AUTHORITIES IN THE
REGION NEAR THE EPICENTER SHOULD BE MADE AWARE OF THIS
POSSIBILITY.

THIS WILL BE THE ONLY BULLETIN ISSUED BY THE PACIFIC TSUNAMI
WARNING CENTER FOR THIS EVENT UNLESS ADDITIONAL INFORMATION
BECOMES AVAILABLE.

THE JAPAN METEOROLOGICAL AGENCY MAY ISSUE ADDITIONAL INFORMATION
FOR THIS EVENT. IN THE CASE OF CONFLICTING INFORMATION...THE
MORE CONSERVATIVE INFORMATION SHOULD BE USED FOR SAFETY.

Preferred Location Parameters

ParameterValueUncertainty
Magnitude6.7 MwpNot Specified
Location4.842°S, 134.085°E± 12.8 km
Depth24.7 km± 7.3 km
Number of Stations Used142
Number of Phases Used145
Minimum Distance295.0 km (2.65°)
Travel Time Residual1.08 sec
Azimuthal Gap28°
Review StatusREVIEWED
Event IDusb000d4u2
Fonte: USGS

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por Diário de um Bombeiro às 19:47

Quinta-feira, 11.10.12

Sismo de magnitude 5,7 registado no Chile

Um forte sismo de magnitude 5,7 na escala de Richter foi registado, esta quinta-feira, no centro do Chile e sentido na capital mas sem provocar estragos importantes, referiram os organismos especializados no Chile.

O abalo prolongado ocorreu às 14.23 horas locais (19.23 horas em Lisboa) e segundo as autoridades provocou numerosos cortes de eletricidade e de ligações telefónicas em diversas regiões de Santiago do Chile.

O Gabinete nacional chileno das situações de urgência (Onemi) precisou que o epicentro do sismo se situou nas regiões de Coquimbo (norte) e El Maule (sul), mas "não foi registada qualquer vítima nem danos de infraestruturas".

No centro de Santiago, forma evacuados diversos edifícios.

Fonte: JN

Tectonic Summary

Seismotectonics of South America (Nazca Plate Region)

The South American arc extends over 7,000 km, from the Chilean margin triple junction offshore of southern Chile to its intersection with the Panama fracture zone, offshore of the southern coast of Panama in Central America. It marks the plate boundary between the subducting Nazca plate and the South America plate, where the oceanic crust and lithosphere of the Nazca plate begin their descent into the mantle beneath South America. The convergence associated with this subduction process is responsible for the uplift of the Andes Mountains, and for the active volcanic chain present along much of this deformation front. Relative to a fixed South America plate, the Nazca plate moves slightly north of eastwards at a rate varying from approximately 80 mm/yr in the south to approximately 65 mm/yr in the north. Although the rate of subduction varies little along the entire arc, there are complex changes in the geologic processes along the subduction zone that dramatically influence volcanic activity, crustal deformation, earthquake generation and occurrence all along the western edge of South America.

Most of the large earthquakes in South America are constrained to shallow depths of 0 to 70 km resulting from both crustal and interplate deformation. Crustal earthquakes result from deformation and mountain building in the overriding South America plate and generate earthquakes as deep as approximately 50 km. Interplate earthquakes occur due to slip along the dipping interface between the Nazca and the South American plates. Interplate earthquakes in this region are frequent and often large, and occur between the depths of approximately 10 and 60 km. Since 1900, numerous magnitude 8 or larger earthquakes have occurred on this subduction zone interface that were followed by devastating tsunamis, including the 1960 M9.5 earthquake in southern Chile, the largest instrumentally recorded earthquake in the world. Other notable shallow tsunami-generating earthquakes include the 1906 M8.5 earthquake near Esmeraldas, Ecuador, the 1922 M8.5 earthquake near Coquimbo, Chile, the 2001 M8.4 Arequipa, Peru earthquake, the 2007 M8.0 earthquake near Pisco, Peru, and the 2010 M8.8 Maule, Chile earthquake located just north of the 1960 event.

Large intermediate-depth earthquakes (those occurring between depths of approximately 70 and 300 km) are relatively limited in size and spatial extent in South America, and occur within the Nazca plate as a result of internal deformation within the subducting plate. These earthquakes generally cluster beneath northern Chile and southwestern Bolivia, and to a lesser extent beneath northern Peru and southern Ecuador, with depths between 110 and 130 km. Most of these earthquakes occur adjacent to the bend in the coastline between Peru and Chile. The most recent large intermediate-depth earthquake in this region was the 2005 M7.8 Tarapaca, Chile earthquake.

Earthquakes can also be generated to depths greater than 600 km as a result of continued internal deformation of the subducting Nazca plate. Deep-focus earthquakes in South America are not observed from a depth range of approximately 300 to 500 km. Instead, deep earthquakes in this region occur at depths of 500 to 650 km and are concentrated into two zones: one that runs beneath the Peru-Brazil border and another that extends from central Bolivia to central Argentina. These earthquakes generally do not exhibit large magnitudes. An exception to this was the 1994 Bolivian earthquake in northwestern Bolivia. This M8.2 earthquake occurred at a depth of 631 km, making it the largest deep-focus earthquake instrumentally recorded, and was felt widely throughout South and North America.

Subduction of the Nazca plate is geometrically complex and impacts the geology and seismicity of the western edge of South America. The intermediate-depth regions of the subducting Nazca plate can be segmented into five sections based on their angle of subduction beneath the South America plate. Three segments are characterized by steeply dipping subduction; the other two by near-horizontal subduction. The Nazca plate beneath northern Ecuador, southern Peru to northern Chile, and southern Chile descend into the mantle at angles of 25° to 30°. In contrast, the slab beneath southern Ecuador to central Peru, and under central Chile, is subducting at a shallow angle of approximately 10° or less. In these regions of “flat-slab” subduction, the Nazca plate moves horizontally for several hundred kilometers before continuing its descent into the mantle, and is shadowed by an extended zone of crustal seismicity in the overlying South America plate. Although the South America plate exhibits a chain of active volcanism resulting from the subduction and partial melting of the Nazca oceanic lithosphere along most of the arc, these regions of inferred shallow subduction correlate with an absence of volcanic activity.

Preferred Location Parameters

ParameterValueUncertainty
Magnitude5.5 mb± 0.03
Location32.867°S, 70.401°W± 17.7 km
Depth81.9 km± 7.9 km
Number of Stations Used376
Number of Phases Used377
Minimum Distance40.1 km (0.36°)
Travel Time Residual0.82 sec
Azimuthal Gap63°
Review StatusREVIEWED
Event IDusb000d4jf
Fonte: USGS

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por Diário de um Bombeiro às 21:30

Quarta-feira, 03.10.12

Sismo de 5.7 a 166km WNW de Sikabaluan, Indonesia


Event Time

  1. 2012-10-03 13:32:34 UTC
  2. 2012-10-03 20:32:34 UTC+07:00 at epicenter
  3. 2012-10-03 14:32:34 UTC+01:00 system time

Location

0.451°S 97.648°E depth=10.0km (6.2mi)

Nearby Cities

  1. 166km (103mi) WNW of Sikabaluan, Indonesia
  2. 269km (167mi) SW of Padangsidempuan, Indonesia
  3. 273km (170mi) SSW of Sibolga, Indonesia
  4. 275km (171mi) W of Pariaman, Indonesia
  5. 599km (372mi) SW of Kuala Lumpur, Malaysia

Preferred Location Parameters

ParameterValueUncertainty
Magnitude5.7 MwbNot Specified
Location0.451°S, 97.648°E± 5.3 km
Depth10.0 kmNot Specified
Number of Stations Used191
Number of Phases Used191
Minimum Distance194.1 km (1.74°)
Travel Time Residual0.93 sec
Azimuthal Gap29°
Review StatusREVIEWED
Event IDusc000d0c8
Fonte: USGS

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por Diário de um Bombeiro às 17:54

Quarta-feira, 03.10.12

Sismo de 5.3 a 202km S de Taron, PNG

De acordo com os últimos 51 registros sísmicos reportados nas últimas 48 horas, o evento de maior intensidade ocorreuna Nova Bretanha, em Papua Nova Guiné, às 06:26 UTC do dia 03/10. O evento foi localizado a 30 km e de profundidade e segundo o USGS, Instituto de Pesquisas geológicas dos EUA, a magnitude do tremor foi calculada em 5.3 graus. Do total de eventos, 43 deles foram classificados como de intensidade leve e 8 atingiram o status de moderados.

ParameterValueUncertainty
Magnitude5.3 mb± 0.05
Location6.277°S, 152.746°E± 14.7 km
Depth30.5 km± 7.4 km
Number of Stations Used156
Number of Phases Used159
Minimum Distance239.3 km (2.15°)
Travel Time Residual0.87 sec
Azimuthal Gap44°
Review StatusREVIEWED
Event IDusc000d07t

Fonte: USGS

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por Diário de um Bombeiro às 09:13

Quarta-feira, 03.10.12

Sismo de 5.3 a 281km NNW de Scott Island Bank, Antarctica


Seismotectonics of the Eastern Margin of the Australia Plate



The eastern margin of the Australia plate is one of the most sesimically active areas of the world due to high rates of convergence between the Australia and Pacific plates. In the region of New Zealand, the 3000 km long Australia-Pacific plate boundary extends from south of Macquarie Island to the southern Kermadec Island chain. It includes an oceanic transform (the Macquarie Ridge), two oppositely verging subduction zones (Puysegur and Hikurangi), and a transpressive continental transform, the Alpine Fault through South Island, New Zealand.

Since 1900 there have been 15 M7.5+ earthquakes recorded near New Zealand. Nine of these, and the four largest, occurred along or near the Macquarie Ridge, including the 1989 M8.2 event on the ridge itself, and the 2004 M8.1 event 200 km to the west of the plate boundary, reflecting intraplate deformation. The largest recorded earthquake in New Zealand itself was the 1931 M7.8 Hawke's Bay earthquake, which killed 256 people. The last M7.5+ earthquake along the Alpine Fault was 170 years ago; studies of the faults' strain accumulation suggest that similar events are likely to occur again.

North of New Zealand, the Australia-Pacific boundary stretches east of Tonga and Fiji to 250 km south of Samoa. For 2,200 km the trench is approximately linear, and includes two segments where old (>120 Myr) Pacific oceanic lithosphere rapidly subducts westward (Kermadec and Tonga). At the northern end of the Tonga trench, the boundary curves sharply westward and changes along a 700 km-long segment from trench-normal subduction, to oblique subduction, to a left lateral transform-like structure.

Australia-Pacific convergence rates increase northward from 60 mm/yr at the southern Kermadec trench to 90 mm/yr at the northern Tonga trench; however, significant back arc extension (or equivalently, slab rollback) causes the consumption rate of subducting Pacific lithosphere to be much faster. The spreading rate in the Havre trough, west of the Kermadec trench, increases northward from 8 to 20 mm/yr. The southern tip of this spreading center is propagating into the North Island of New Zealand, rifting it apart. In the southern Lau Basin, west of the Tonga trench, the spreading rate increases northward from 60 to 90 mm/yr, and in the northern Lau Basin, multiple spreading centers result in an extension rate as high as 160 mm/yr. The overall subduction velocity of the Pacific plate is the vector sum of Australia-Pacific velocity and back arc spreading velocity: thus it increases northward along the Kermadec trench from 70 to 100 mm/yr, and along the Tonga trench from 150 to 240 mm/yr.

The Kermadec-Tonga subduction zone generates many large earthquakes on the interface between the descending Pacific and overriding Australia plates, within the two plates themselves and, less frequently, near the outer rise of the Pacific plate east of the trench. Since 1900, 40 M7.5+ earthquakes have been recorded, mostly north of 30°S. However, it is unclear whether any of the few historic M8+ events that have occurred close to the plate boundary were underthrusting events on the plate interface, or were intraplate earthquakes. On September 29, 2009, one of the largest normal fault (outer rise) earthquakes ever recorded (M8.1) occurred south of Samoa, 40 km east of the Tonga trench, generating a tsunami that killed at least 180 people.

Across the North Fiji Basin and to the west of the Vanuatu Islands, the Australia plate again subducts eastwards beneath the Pacific, at the North New Hebrides trench. At the southern end of this trench, east of the Loyalty Islands, the plate boundary curves east into an oceanic transform-like structure analogous to the one north of Tonga.

Australia-Pacific convergence rates increase northward from 80 to 90 mm/yr along the North New Hebrides trench, but the Australia plate consumption rate is increased by extension in the back arc and in the North Fiji Basin. Back arc spreading occurs at a rate of 50 mm/yr along most of the subduction zone, except near ~15°S, where the D'Entrecasteaux ridge intersects the trench and causes localized compression of 50 mm/yr in the back arc. Therefore, the Australia plate subduction velocity ranges from 120 mm/yr at the southern end of the North New Hebrides trench, to 40 mm/yr at the D'Entrecasteaux ridge-trench intersection, to 170 mm/yr at the northern end of the trench.

Large earthquakes are common along the North New Hebrides trench and have mechanisms associated with subduction tectonics, though occasional strike slip earthquakes occur near the subduction of the D'Entrecasteaux ridge. Within the subduction zone 34 M7.5+ earthquakes have been recorded since 1900. On October 7, 2009, a large interplate thrust fault earthquake (M7.6) in the northern North New Hebrides subduction zone was followed 15 minutes later by an even larger interplate event (M7.8) 60 km to the north. It is likely that the first event triggered the second of the so-called earthquake "doublet".

Preferred Location Parameters

ParameterValueUncertainty
Magnitude5.3 mb± 0.08
Location65.008°S, 177.926°E± 24.2 km
Depth16.6 km± 6.7 km
Number of Stations Used54
Number of Phases Used54
Minimum Distance1485.0 km (13.34°)
Travel Time Residual1.36 sec
Azimuthal Gap93°
Review StatusREVIEWED
Event IDusc000czu9
Fonte: USGS

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por Diário de um Bombeiro às 01:30

Quarta-feira, 03.10.12

Sismo Próximo de Fukushima

De acordo com os últimos 71 registros sísmicos reportados nas últimas 48 horas, o evento de maior intensidade ocorreupróximo à costa leste de Honshu, no Japão, às 22:21 UTC do dia 01/10. O evento foi localizado a 9 km e de profundidade e segundo o USGS, Instituto de Pesquisas geológicas dos EUA, a magnitude do tremor foi calculada em 6.2 graus. Do total de eventos, 59 deles foram classificados como de intensidade leve e 11 atingiram o status de moderados. Apenas um dos tremores foi classificado entre forte e muito forte.

Por: Marco António em SP

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por Diário de um Bombeiro às 01:25

Domingo, 30.09.12

Sismo 4.7 North Indian Ocean


Event Time

  1. 2012-09-30 20:43:38 UTC
  2. 2012-10-01 02:43:38 UTC+06:00 at epicenter
  3. 2012-09-30 21:43:38 UTC+01:00 system time

Location

2.521°N 89.939°E depth=15.0km (9.3mi)

Nearby Cities

  1. 685km (426mi) WSW of Banda Aceh, Indonesia
  2. 704km (437mi) WSW of Sabang, Indonesia
  3. 710km (441mi) WSW of Meulaboh, Indonesia
  4. 716km (445mi) W of Sinabang, Indonesia
  5. 1220km (758mi) ESE of Colombo, Sri Lanka

Preferred Location Parameters

ParameterValueUncertainty
Magnitude4.7 mb± 0.17
Location2.521°N, 89.939°E± 39.2 km
Depth15.0 km± 7.6 km
Number of Stations Used33
Number of Phases Used34
Minimum Distance833.8 km (7.49°)
Travel Time Residual0.55 sec
Azimuthal Gap199°
Review StatusREVIEWED
Event IDusc000cyjw
Fonte: USGS

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por Diário de um Bombeiro às 23:01

Domingo, 30.09.12

Sismo de M7.3 a 10km WNW de Isnos, Colombia


Event Time

  1. 2012-09-30 16:31:35 UTC
  2. 2012-09-30 11:31:35 UTC-05:00 at epicenter
  3. 2012-09-30 17:31:35 UTC+01:00 system time

Location

1.972°N 76.329°W depth=162.1km (100.7mi)

Nearby Cities

  1. 10km (6mi) WNW of Isnos, Colombia
  2. 34km (21mi) WNW of Pitalito, Colombia
  3. 60km (37mi) SSE of Popayan, Colombia
  4. 67km (42mi) SW of La Plata, Colombia
  5. 344km (214mi) NE of Quito, Ecuador

Tectonic Summary

The September 30, 2012 M 7.3 earthquake west of Isnos, Colombia, occurred as a result of normal faulting deep within the subducting Nazca slab. The earthquake ruptured a fault in the interior of the inclined subduction zone that dips to the east-northeast beneath South America, having begun its decent into the mantle at the South America trench offshore of Colombia and Ecuador. The event resulted from stresses generated by the slow distortion of the subducting plate as it descends through the mantle, rather than on the thrust interface that constitutes the boundary between the Nazca and overlying South America plates; the latter is active only near the Earth's surface, while the subducting Nazca plate generates intraplate earthquakes to depths of 200 km or more in this region. At the latitude of this event, the Nazca plate moves east-northeast with respect to the South America plate at a rate of approximately 60 mm/yr.

Deep earthquakes in this region of the Nazca plate are not uncommon; there have been 13 similar events deeper than 100 km over the past 40 years, within 500 km of the September 30 2012 earthquake. The largest was a magnitude 7.1 earthquake at a depth of 206 km in August of 2010, 380 km to the south of the September 30 event.

Seismotectonics of South America (Nazca Plate Region)

The South American arc extends over 7,000 km, from the Chilean margin triple junction offshore of southern Chile to its intersection with the Panama fracture zone, offshore of the southern coast of Panama in Central America. It marks the plate boundary between the subducting Nazca plate and the South America plate, where the oceanic crust and lithosphere of the Nazca plate begin their descent into the mantle beneath South America. The convergence associated with this subduction process is responsible for the uplift of the Andes Mountains, and for the active volcanic chain present along much of this deformation front. Relative to a fixed South America plate, the Nazca plate moves slightly north of eastwards at a rate varying from approximately 80 mm/yr in the south to approximately 65 mm/yr in the north. Although the rate of subduction varies little along the entire arc, there are complex changes in the geologic processes along the subduction zone that dramatically influence volcanic activity, crustal deformation, earthquake generation and occurrence all along the western edge of South America.

Most of the large earthquakes in South America are constrained to shallow depths of 0 to 70 km resulting from both crustal and interplate deformation. Crustal earthquakes result from deformation and mountain building in the overriding South America plate and generate earthquakes as deep as approximately 50 km. Interplate earthquakes occur due to slip along the dipping interface between the Nazca and the South American plates. Interplate earthquakes in this region are frequent and often large, and occur between the depths of approximately 10 and 60 km. Since 1900, numerous magnitude 8 or larger earthquakes have occurred on this subduction zone interface that were followed by devastating tsunamis, including the 1960 M9.5 earthquake in southern Chile, the largest instrumentally recorded earthquake in the world. Other notable shallow tsunami-generating earthquakes include the 1906 M8.5 earthquake near Esmeraldas, Ecuador, the 1922 M8.5 earthquake near Coquimbo, Chile, the 2001 M8.4 Arequipa, Peru earthquake, the 2007 M8.0 earthquake near Pisco, Peru, and the 2010 M8.8 Maule, Chile earthquake located just north of the 1960 event.

Large intermediate-depth earthquakes (those occurring between depths of approximately 70 and 300 km) are relatively limited in size and spatial extent in South America, and occur within the Nazca plate as a result of internal deformation within the subducting plate. These earthquakes generally cluster beneath northern Chile and southwestern Bolivia, and to a lesser extent beneath northern Peru and southern Ecuador, with depths between 110 and 130 km. Most of these earthquakes occur adjacent to the bend in the coastline between Peru and Chile. The most recent large intermediate-depth earthquake in this region was the 2005 M7.8 Tarapaca, Chile earthquake.

Earthquakes can also be generated to depths greater than 600 km as a result of continued internal deformation of the subducting Nazca plate. Deep-focus earthquakes in South America are not observed from a depth range of approximately 300 to 500 km. Instead, deep earthquakes in this region occur at depths of 500 to 650 km and are concentrated into two zones: one that runs beneath the Peru-Brazil border and another that extends from central Bolivia to central Argentina. These earthquakes generally do not exhibit large magnitudes. An exception to this was the 1994 Bolivian earthquake in northwestern Bolivia. This M8.2 earthquake occurred at a depth of 631 km, making it the largest deep-focus earthquake instrumentally recorded, and was felt widely throughout South and North America.

Subduction of the Nazca plate is geometrically complex and impacts the geology and seismicity of the western edge of South America. The intermediate-depth regions of the subducting Nazca plate can be segmented into five sections based on their angle of subduction beneath the South America plate. Three segments are characterized by steeply dipping subduction; the other two by near-horizontal subduction. The Nazca plate beneath northern Ecuador, southern Peru to northern Chile, and southern Chile descend into the mantle at angles of 25° to 30°. In contrast, the slab beneath southern Ecuador to central Peru, and under central Chile, is subducting at a shallow angle of approximately 10° or less. In these regions of “flat-slab” subduction, the Nazca plate moves horizontally for several hundred kilometers before continuing its descent into the mantle, and is shadowed by an extended zone of crustal seismicity in the overlying South America plate. Although the South America plate exhibits a chain of active volcanism resulting from the subduction and partial melting of the Nazca oceanic lithosphere along most of the arc, these regions of inferred shallow subduction correlate with an absence of volcanic activity.



Estimated Fatalities







Preferred Location Parameters

ParameterValueUncertainty
Magnitude7.3 MwbNot Specified
Location1.972°N, 76.329°W± 2.9 km
Depth162.1 km± 6.4 km
Number of Stations Used800
Number of Phases Used800
Minimum Distance388.7 km (3.49°)
Travel Time Residual0.92 sec
Azimuthal Gap15°
Review StatusPUBLISHED
Event IDus2012gdap




Fonte: USGS

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por Diário de um Bombeiro às 19:41

Sábado, 29.09.12

Sismo de 4.5 a 210km E de Miyako, Japan


Seismotectonics of Japan and Vicinity

Japan and the surrounding islands straddle four major tectonic plates: Pacific plate; North America plate; Eurasia plate; and Philippine Sea plate. The Pacific plate is subducted into the mantle, beneath Hokkaido and northern Honshu, along the eastern margin of the Okhotsk microplate, a proposed subdivision of the North America plate. Farther south, the Pacific plate is subducted beneath volcanic islands along the eastern margin of the Philippine Sea plate. This 2,200 km-long zone of subduction of the Pacific plate is responsible for the creation of the deep offshore Ogasawara and Japan trenches as well as parallel chains of islands and volcanoes, typical of Circumpacific island arcs. Similarly, the Philippine Sea plate is itself subducting under the Eurasia plate along a zone, extending from Taiwan to southern Honshu that comprises the Ryukyu Islands and the Nansei-Shoto trench.

Subduction zones at the Japanese island arcs are geologically complex and produce numerous earthquakes from multiple sources. Deformation of the overriding plates generates shallow crustal earthquakes, whereas slip at the interface of the plates generates interplate earthquakes that extend from near the base of the trench to depths of 40 to 60 km. At greater depths, Japanese arc earthquakes occur within the subducting Pacific and Philippine Sea plates and can reach depths of nearly 700 km. Since 1900, three great earthquakes occurred off Japan and three north of Hokkaido. They are the M8.4 1933 Sanriku-oki earthquake, the M8.3 2003 Tokachi-oki earthquake, the M9.0 2011 Tohoku earthquake, the M8.4 1958 Etorofu earthquake, the M8.5 1963 Kuril earthquake, and the M8.3 1994 Shikotan earthquake.



Preferred Location Parameters

ParameterValueUncertainty
Magnitude4.5 mb± 0.27
Location39.540°N, 144.402°E± 22.8 km
Depth10.0 km± 2.3 km
Number of Stations Used21
Number of Phases Used24
Minimum Distance295.0 km (2.65°)
Travel Time Residual1.05 sec
Azimuthal Gap153°
Review StatusREVIEWED
Event IDusc000cya6


Fonte: USGS

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por Diário de um Bombeiro às 23:45


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