Mw 7.8, Muisne, Ecuador Fri, 16 April 2016 at 23:58:37 UTC Earthquake overview Caribbean plate A moment magnitude Mw 7.8 earthquake was registered offshore of the west coast of northern Ecuador Epicentre was located 170km (105.6mi) north west of the capital city Quito. Last earthquake in the same region occurred on May 14th, 1942 (Mw 7.8) Until now over 400 fatalities and thousands injuries has been reported. Cocos plate Nazca plate South American plate M 7.8 2016/04/16 Image courtesy of Google Earth. 1

Shaking Intensity – Modified Mercalli Intensity Scale (MMI) Mw 7.8, Muisne, Ecuador Fri, 16 April 2016 at 23:58:37 UTC Earthquake hazard map Localized regions of Strong shaking can be seen in various regions to the south of the epicentre Shaking Intensity – Modified Mercalli Intensity Scale (MMI) 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 2

Map with MMI contour overlay. Mw 7.8, Muisne, Ecuador Fri, 16 April 2016 at 23:58:37 UTC Earthquake hazard map Orange alert level for shaking-related fatalities and economic losses Estimated economic losses are < 1% of GDP of Ecuador USGS PAGER Map with MMI contour overlay. Images courtesy of the US Geological Survey

Peak Ground Acceleration (PGA) Mw 7.8, Muisne, Ecuador Fri, 16 April 2016 at 23:58:37 UTC Peak Ground Acceleration (PGA) 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 around to 35% of g value which corresponds to approximately 3.43 ms-2 Image courtesy of US Geological Survey

Mw 7.8, Muisne, Ecuador Fri, 16 April 2016 at 23:58:37 UTC Earthquake slip model N/S transform faults Above: Graph displaying the total energy release over time for the rupture. Most of the energy was released after 20 seconds of the beginning of the earthquake Right: Cross section of the preliminary slip model generated by the USGS from seismic data using the ruptured plotted on the map Images courtesy of US Geological Survey

Historical seismicity Mw 7.8, Muisne, Ecuador Fri, 16 April 2016 at 23:58:37 UTC Historical seismicity Colombia In the northern segment of the South American margin, few large events are present in catalogues Since 1906, after a Mw ~8.8 earthquake, few events with lower magnitudes (Mw 7.8, 1942; Mw 8.1, 1979) occurred in the affected area The Mw 7.8, 2016 earthquake is located at the southern end of the ruptured generated by the Mw ~8.8, 1906 earthquake Ecuador Plates Convergence zone Peru M 7.8 2016/04/16 M 7.0 2016/04/15 Image extracted from Bilek et al, 2009. Seismicity along the South American subduction zone: Review of large earthquakes, tsunamis, and subduction zone complexity. Red dot indicate the epicentre of the 2016 Ecuador earthquake 6

Mw 7.8, Muisne, Ecuador Fri, 16 April 2016 at 23:58:37 UTC Tectonic setting This earthquake occurred offshore of the west coast of northern Ecuador, as a result of a thrust faulting near the plate boundary between the Nazca and South American plates At the location of the earthquake, Nazca plate subducts eastward beneath the South American plate at a relative velocity of 61 mm/yr Subduction process led to the uplift of the Andes mountain and presence of active volcanic chain along the deformation front Occurrence of large thrust earthquakes is common in this convergent region Map showing the location of the plate boundary, subduction zone and the epicentre of the Ecuador Mw 7.8 earthquake 2016 7

Earthquake focal mechanism Mw 7.8, Muisne, Ecuador Fri, 16 April 2016 at 23:58:37 UTC Earthquake focal mechanism The depth of this earthquake is 24 km, which can be associated to a plate interface earthquake The focal mechanism shows that the earthquake has a reverse mechanism in agreement with the tectonic setting of the region Cocos Plate Nazca Plate South American Plate Above: Corresponding focal mechanism for the Ecuador earthquake (obtained from USGS) Above: Rupture of a reverse fault showing the convergence of two blocks indicated by arrows, displacement is indicated by thin black arrows Below: Location of the earthquake (yellow star) 8

Seismic waves recorded in the UK Mw 7.8, Muisne, Ecuador Fri, 16 April 2016 at 23:58:37 UTC Seismic waves recorded in the UK P S Even though the earthquake occurred more that 9000 km (~5600 miles) from the UK, the seismic waves emitted by this earthquake can still be measured. The plot above shows the vertical 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 right hand side of the slide. 9

Mw 7.8, Muisne, Ecuador Fri, 16 April 2016 at 23:58:37 UTC Find more BGS (British Geological Survey) – seismology and earthquakes – frequently asked questions GO! IRIS (Incorporated Research Institutions for Seismology) – learning about earthquakes GO! UK School Seismology Project – classroom activities, videos and support documents GO! USGS (United States Geological Survey) – FAQs, glossary, posters, animations GO! USGS summary of the earthquake GO! 10

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