Pakistan A magnitude 7.5 earthquake struck in North East Afghanistan; the epicentre was centered about 48.0 km (≈ 30.0 miles) SSW of Jurm. The depth has

Pakistan

A magnitude 7.5 earthquake struck in North East Afghanistan; the epicentre was centered about 48.0 km (≈ 30.0 miles) SSW of Jurm. The depth has been estimated to be about 220 km (~135 miles).

At least 40 people have been killed in Pakistan and 20 in Afghanistan and more than 100 have been reported to be injured as a result of the earthquake. Reports say shaking was sustained for about one minute. Mass panic ensued as a result of the shaking and it has caused significant damage to building and infrastructure.

Shaking has been felt as far as Delhi, India.

Images courtesy of Google Earth.

Magnitude 7.5, NORTHERN AFGHANISTANMonday, 26 October, 2015 at 09:09:32 UTC

INDIA

AFGHANISTAN

PAKISTAN

KABUL

Earthquake location & overview

Shaking Intensity – Modified Mercalli Intensity Scale (MMI)

Strong (VI) into rather strong (VII) shaking was felt inside about a 200 km radius from the epicentre. Moderate (IV) shaking was experienced through most of the surrounding region.

I. Instrumental

Not felt by many people unless in favourable conditions.

II. Weak Felt only by a few people at best, especially on the upper floors of buildings. Delicately suspended objects may swing.

III. Slight Felt quite noticeably by people indoors, especially on the upper floors of buildings. Many to do not recognise it as an earthquake. Standing motor cars may rock slightly. Vibration similar to the passing of a truck. Duration estimated.

IV. Moderate

Felt indoors by many people, outdoors by a few people during the day. At night, some awakened.

V. Rather Strong

Felt outside by most, may not be felt by some people in non-favourable conditions. Dishes and windows may break and large bells will ring. Vibrations like train passing close to house.

VI. Strong Felt by all; many frightened and run outdoors, walk unsteadily. Windows, dishes, glassware broken; books fall off shelves; some heavy furniture moved or overturned; a few instances of fallen plaster. Damage slight.

VII. Very Strong

Difficult to stand; furniture broken; damage negligible in building of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken. Noticed by people driving motor cars.

VIII. Destructive

Damage slight in specially designed structures; considerable in ordinary substantial buildings with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture moved.

IX. Violent General panic; damage considerable in poorly designed structures, well designed frame structures thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations.

X. Intense Some well build wooden structures destroyed; most masonry and frame structures destroyed with foundation. Rails bent.

XI. Extreme Few, if any masonry structures remain standing. Bridges destroyed. Rails bent greatly.

XII. Cataclysmic

Total destruction – everything is destroyed. Lines of sight and level distorted. Objects thrown into the air. The ground moves in waves or ripples. Large amounts of rock move position. Landscape altered, or leveled by several meters. In some cases, even the routes of rivers are changed.

Image courtesy of US Geological Survey.


USGS PAGER Map with MMI contour overlay.

Orange alert level for shaking-related fatalities. Significant casualties are likely and the disaster is potentially widespread. Past events with this alert level have required a regional or national level response. Yellow alert level for economic losses. Some damage is possible. Estimated economic losses are less than 1% of GDP of Afghanistan.

Images courtesy of the US Geological Survey.


Right: A Peak Ground Acceleration (PGA) map produced by the USGS. Each contour represents the acceleration of the ground as a percentage of g (≈ 9.81 ms-2). The most intense shaking was experienced within a 20 km radius at ≥ 0.42 g (≈ 4.12 ms-2).

Image courtesy of US Geological Survey.



Top right: A preliminary slip model generated by the USGS from seismic data. Bottom right: A cross section of the preliminary slip model generated by the USGS from seismic data.

Above: A graph displaying total energy release over time for the rupture. The most energy release occurred approximately 15 seconds after the start of the earthquake.

Images courtesy of US Geological Survey.

Earthquake slip models


Interferogram from

insarap.org

Himalayas is one of the most tectonically active areas in the world. There are a lot of large earthquakes that have occurred in this area. In last century there have been nearly 160 earthquakes with magnitude greater than 6 in this area. This includes seven earthquakes with a magnitude of greater than 7.0.In March 2002 just 20 km from this event, there was a magnitude 7.4 earthquake. The event in 2002 at a similar depth was also a thrust fault earthquake. The 2002 event caused over 150 fatalities and the damage or destruction of over 400 houses in relation to an associated landslide.

M 7.42002/03/03

M 7.52015/10/26

M 7.62005/10/08

Historical seismicity


The depth of this earthquake is 220 km, which is known as an intermediate-depth earthquake. The focal mechanism shows that this earthquake has a thrust mechanism.

This is unusually deep for a thrust earthquake, which usually occur on the boundary between two plates. This cannot be the case for this intermediate depth earthquake. The potential causes of this earthquake are discussed on the next slide.

Left: Focal mechanism of the

earthquake showing reverse faulting (from

the USGS)

Earthquake mechanism

Below: A map of the extent of the slip along the deep thrust fault.

Left: Diagram showing the mechanism of a thrust fault


In this area, the India plate under moving northward beneath the Eurasia plate at about 38-45 milometers a year.

The friction between these two plates can cause large earthquakes like the recent Nepal earthquake, but this is not what caused this earthquake.

This event occurred much deeper, probably in ancient oceanic crust that was subducted before the Indian plate collided with Eurasia. This thrusting earthquake is likely due to the stresses between the subducted continental crust, and much older subducted oceanic crust.

Indian plate

Eurasian plate

Above: Map showing the location of the collision plate boundary fault and the

earthquake Left: A schematic diagram showing the subduction of oceanic crust, followed be

thicker continental crust

Tectonic setting


S-wavesP-waves Surface waves

Seismic waves recorded in the UK

• Even though the earthquake occurred more that 6,000 km (~3800 miles) from the UK, the seismic waves emitted by this earthquake can still be measured.

• The plot above shows the horizontal (East-West) component of the seismic waves measured at seismic stations across the UK. The colour of the line corresponds to the station at which it was recorded, shown on the map on the left hand side of the slide.

• The P-wave and S-wave arrivals can be clearly seen, but the surface wave arrivals have a lower amplitude than other earthquakes, as the source is so deep in this case.

10

Find out more….

• University of Liverpool ‘Viewpoint’ article on the earthquake http://news.liv.ac.uk/2015/10/27/viewpoint-deep-thrust-earthquake-in-northern-afghanistan/

• BGS (British Geological Survey) – seismology and earthquakes – frequently asked questions http://www.earthquakes.bgs.ac.uk/education/faqs/faq_index.html

• IRIS (Incorporated Research Institutions for Seismology) – learning about earthquakes http://www.iris.edu/hq/programs/education_and_outreach/students

• UK School Seismology Project – classroom activities, videos and support documents http://www.bgs.ac.uk/schoolseismology/home.html

• USGS (United States Geological Survey) – FAQs, glossary, posters, animations http://earthquake.usgs.gov/learn/

• USGS summary of the earthquake http://earthquake.usgs.gov/earthquakes/eventpage/us10003re5#general_summary


Documents

Pakistan A magnitude 7.5 earthquake struck in North East Afghanistan; the epicentre was centered about 48.0 km (≈ 30.0 miles) SSW of Jurm. The depth has