Magnitude 8.2 IQUIQUE, NORTHERN CHILETuesday, 1 April, 2014 at 23:46:46 UTC

Pakistan

A magnitude 8.2 earthquake struck off the coast of northern Chile, generating a local tsunami of (~2m). The earthquake’s epicentre was centred around 95 km (59 miles) northwest of Iquique. The earthquake's depth is believed around 20 km (12.5 miles).

At least five fatalities have been recorded. Other effects of the earthquake have included power cuts, fires and landslides.

Shaking intensity

Very strong (VII) to severe shaking (VII) was felt in nearby settlements. The earthquake was also felt in southern Peru and Antofagasta in north-central Chile.

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.

Magnitude 8.2 IQUIQUE, NORTHERN CHILETuesday, 1 April, 2014 at 23:46:46 UTC

USGS PAGER Population Exposed to Earthquake Shaking

Orange alert level for economic losses. Significant damage is likely and the disaster is potentially widespread. Estimated economic losses are less than 1% of GDP of Chile. Past events with this alert level have required a regional or national level response.

Yellow alert level for shaking-related fatalities. Some casualties are possible.

Images courtesy of the US Geological Survey

Magnitude 8.2 IQUIQUE, NORTHERN CHILETuesday, 1 April, 2014 at 23:46:46 UTC

Iran

Pakistan

Earthquake and historic seismicity

Magnitude 8.2 IQUIQUE, NORTHERN CHILETuesday, 1 April, 2014 at 23:46:46 UTC

The April 1st earthquake occurred in a region of historic seismic quiescence – named the northern Chile or Iquique seismic gap. Historical records indicate a magnitude 8.8 earthquake occurred within the Iquique gap in 1877, which was preceded immediately to the north by an magnitude 8.8 earthquake in 1868. To the south the Iquique seismic gap, there were two big earthquakes with magnitude 7.6 and 8.1 in 2007 and 1995, respectively.

Previous large earthquake ruptures in northern Chile

M > 5.5 seismicity in the region since 1970

Tectonic interpretation

Tectonic setting plotted using plate boundary data from the USGS.

Focal mechanism of the oblique-strike-slip

earthquake (Copyright USGS).

Diagram showing the typical motion of a

megathrust earthquake

67 mm/yr

Nazca Plate

South AmericanPlate

The April 1, 2014 M 8.2 earthquake occurred as the result of thrust faulting at shallow depths just offshore of the Chilean coast. The location and mechanism of the earthquake are consistent with slip on the plate boundary interface (megathrust) between the Nazca and South America plates. The Nazca plate subducts eastward beneath the South America plate at a rate of about 67 mm/yr at the latitude of the earthquake.

Magnitude 8.2 IQUIQUE, NORTHERN CHILETuesday, 1 April, 2014 at 23:46:46 UTC

Estimates of fault movement and aftershocks

Magnitude 8.2 IQUIQUE, NORTHERN CHILETuesday, 1 April, 2014 at 23:46:46 UTC

M8.2 mainshockepicentre

M 7.6 aftershock

Most aftershocks have so far occurred to the south of the mainshock

Greatest slip (up to 6.5m) during mainshock occurred to the south-east

A preliminary model from the USGS of slip of the fault estimates that during the earthquake, the fault may have moved up to 6.5 m. Most of this movement appears to have occurred to the south-east of the mainshock’s epicentre.

Many strong aftershocks have been recorded in the aftermath of the earthquake. The strongest of these was a Magnitude 7.6 event that occurred in the early hours of Thursday 3rd April. This aftershock was located close to Iquique.

7

Seismogram recordings by various seismometers across the UK

S-waves

Time of earthquake

P-waves Surface waves

Seismic waves took just 13 minutes to travel through the Earth from the earthquake to the UK!

Magnitude 8.2 IQUIQUE, NORTHERN CHILETuesday, 1 April, 2014 at 23:46:46 UTC

8

Seismogram recording from a school seismometer in Liverpool

Magnitude 8.2 IQUIQUE, NORTHERN CHILETuesday, 1 April, 2014 at 23:46:46 UTC

9

Find out more….

• 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 Iquique earthquakehttp://earthquake.usgs.gov/earthquakes/eventpage/usc000nzvd

Magnitude 8.2 IQUIQUE, NORTHERN CHILETuesday, 1 April, 2014 at 23:46:46 UTC