1. A magnitude 7.3 earthquake occurred to the east of Kathmandu, in an area close to Mount Everest. This large earthquake is the largest aftershock so far of the devastating magnitude 7.8 earthquake that occurred 17 days earlier, further north in Nepal. While this earthquake is significantly smaller that the main shock on the 5 th of April 2015, it will be widely felt, and may cause damage, particularly to buildings already damaged by the mainshock. Given the mountainous terrain surrounding the epicenter, it is likely that more landslides and avalanches may be caused. Magnitude 7.3 aftershock in Nepal Tuesday, 12 th May, 2015 at 07:05:19 UTC Location of the magnitude 7.8 main shock Location of the magnitude 7.3 aftershock Introduction

2. In this PowerPoint we will therefore have a slightly different structure. We will: 1.Give an overview of this significant aftershock earthquake 2.Give an update on some of the scientific observations that have been made in the two weeks since the mainshock In this PowerPoint we will therefore have a slightly different structure. We will: 1.Give an overview of this significant aftershock earthquake 2.Give an update on some of the scientific observations that have been made in the two weeks since the mainshock Location of the magnitude 7.8 main shock Location of the magnitude 7.3 aftershock Introduction Magnitude 7.3 aftershock in Nepal Tuesday, 12 th May, 2015 at 07:05:19 UTC A magnitude 7.3 earthquake occurred to the east of Kathmandu, in an area close to Mount Everest. This large earthquake is the largest aftershock so far of the devastating magnitude 7.8 earthquake that occurred 17 days earlier, further north in Nepal. While this earthquake is significantly smaller that the main shock on the 5 th of April 2015, it will be widely felt, and may cause damage, particularly to buildings already damaged by the mainshock. Given the mountainous terrain surrounding the epicenter, it is likely that more landslides and avalanches may be caused.

3. Modified Mercalli Intensity Scale Predicted ground shaking intensity (image courtesy USGS) Where was the earthquake felt? In this magnitude 7.3 earthquake, the greatest shaking is expected to have been very strong (VII) and possibly destructive (VIII) very close to the epicenter. Strong shaking is also expected in the Kathmandu Valley. This is likely to cause damage especially to buildings that are already damaged from the mainshock in April. There is also a large potential for more landslides and avalanches in the mountainous areas close to the epicenter of this aftershock. Magnitude 7.3 aftershock in Nepal Tuesday, 12 th May, 2015 at 07:05:19 UTC

4. Past earthquakes in the region The Himalayas are a very tectonically active part of the world. This means that earthquakes are not uncommon, with several earthquakes that are large enough to be felt occurring every year. Large earthquakes are however more rare. In the aftermath of a large earthquake like that of the 25 th of April, many smaller earthquakes (aftershocks) happen. The likelihood of large earthquakes like this large aftershock is also greatly increased. This aftershock earthquake has occurred at the eastern end of the fault that ruptured in on the 25 th of April. It is likely to have been triggered by the re- distribution of stresses on this fault by the magnitude 7.8 mainshock. Map showing all events of magnitude greater than M 6.5 that have occurred in the area since 1900. The location of the April 2015 earthquake is indicated by the red star. (Earthquake data courtesy of the USGS and map data courtesy of Google Earth) M8.2, Jan 1934 M7.8, 25 th April 2015 M7.3, aftershock, 12 th May 2015 Magnitude 7.3 aftershock in Nepal Tuesday, 12 th May, 2015 at 07:05:19 UTC

5. India plate Eurasia plate 45 mm/yr At the location of this earthquake, the India plate is under-thrusting beneath the Eurasia plate at a rate of about 45 mm per year. This make the region one of the most seismically hazardous on Earth. A series of thrust faults partially accommodate this convergence. The April 25, 2015 M 7.8 Nepal earthquake occurred as a result of thrust faulting on or near the main Himalayan frontal thrust between the India plate and the overriding Eurasia plate to the north. The aftershock on the 12 th May 2015 appears to have ruptured with a very similar thrusting mechanism. Map showing the location of the Himalayan thrust plate boundary fault What caused this earthquake to occur? Cartoon cross-section illustrating the collision between the Indian and Eurasian plates and the likely location of the 2015 earthquake. Indian plate Eurasian plate Mainshock:Aftershock: Focal mechanism of the Nepal earthquake showing thrusting (from the USGS) Magnitude 7.3 aftershock in Nepal Tuesday, 12 th May, 2015 at 07:05:19 UTC

6. Recordings of the earthquake from the British Geological Survey seismometer network Plot similar seismograms yourself at: http://ds.iris.edu/wilber3/find_stations/5111620http://ds.iris.edu/wilber3/find_stations/5111620 These seismometers are located some 7000 km (4500 miles) from the earthquake’s epicentre. The P-waves are the first to arrive, but the later-arriving surface waves have the strongest amplitude. Magnitude 7.3 aftershock in Nepal Tuesday, 12 th May, 2015 at 07:05:19 UTC

7. NEPAL INDIA CHINA Kathmandu Himalaya Aftershocks from M w 7.8 earthquake, 25 th April 2015 This earthquake is the largest in a series of aftershocks of the magnitude 7.8 main shock earthquake that occurred in Nepal on the 25 th of April. The mainshock is shown in red on the map, and magnitude 7.3 aftershock is shown in yellow. Other aftershocks are shown by blue circles. The aftershocks roughly show the area of the Himalayan thrust faults that ruptured on the 25 th of April. You can see that today’s large aftershock occurs at the very end of this rupture area. Map showing all aftershocks with magnitude greater than 4 recorded by the USGS. The mainshock location is given by the red star. (Earthquake data courtesy of the USGS) Magnitude 7.3 aftershock in Nepal Tuesday, 12 th May, 2015 at 07:05:19 UTC Location of the magnitude 7.8 main shock (25 th April 2015) Location of the magnitude 7.3 aftershock (12 th May 2015)

8. Magnitude comparison The magnitude of earthquakes are reported on a logarithmic scale. Meaning that this magnitude 7.3 aftershock is approximately 6 times less powerful than the main shock. On average about 15 earthquakes with 7 – 8 occur every year. Many of these though occur in remote areas of the ocean, or deep in the Earth, and so have a far smaller human impact. 25 th April 2015 Mw 7.8 Nepal main shock 12 th May 2015 Mw 7.3 Nepal after shock 2010 Mw 6.3 L’Aquila, Italy Magnitude 7.3 aftershock in Nepal Tuesday, 12 th May, 2015 at 07:05:19 UTC

9. The 7.8 Mw Nepal Earthquake – an update The fault that ruptured during the Nepal main shock was more than 80 km long, and the amount of slip on this fault varies over its area. The figure to the left shows that in some areas of the fault the slip was as much as 400 cm, and that the largest slip was to the south east of the epicentre. The grey graph in the bottom left shows the amount of energy released from the onset time of the earthquake (0 seconds).

10. The 7.8 Mw Nepal Earthquake – an update

11. The 7.8 Mw Nepal Earthquake – an update Kathmandu valley is built on ancient lake (amplifies ground shaking) Kathmandu Steep snow-covered mountains: avalanches Lack of earthquake- resistant buildings and poor education Villages on steep Himalayan foothills: landslides Shallow depth and large magnitude of earthquake Why was damage so large?

12. USGS webpage for this earthquakehttp://earthquake.usgs.gov/earthquakes/eventpage/us20002926#general_summaryhttp://earthquake.usgs.gov/earthquakes/eventpage/us20002926#general_summary BGS (British Geological Survey) – seismology and earthquakes – frequently asked questions http://www.earthquakes.bgs.ac.uk/education/faqs/faq_index.html http://www.earthquakes.bgs.ac.uk/education/faqs/faq_index.html BBC News article on this earthquake http://www.bbc.co.uk/news/science-environment-32462763http://www.bbc.co.uk/news/science-environment-32462763 IRIS special event page http://ds.iris.edu/ds/nodes/dmc/specialevents/2015/04/25/nepal/http://ds.iris.edu/ds/nodes/dmc/specialevents/2015/04/25/nepal/ IRIS (Incorporated Research Institutions for Seismology) – learning about earthquakes http://www.iris.edu/hq/programs/education_and_outreach/students 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 http://www.bgs.ac.uk/schoolseismology/home.html USGS (United States Geological Survey) – FAQs, glossary, posters, animations http://earthquake.usgs.gov/learn/ http://earthquake.usgs.gov/learn/ EMSC (European Mediterranean Seismological Centre) http://www.emsc- csem.org/http://www.emsc- csem.org/ Find out more … Saturday, 25 April, 2015 at 06:11:26 UTC Magnitude 7.8 earthquake Nepal