Part 2: WORLD SEISMICITY
Use the following website to observe the most recent seismicity, http://ds.iris.edu/seismon/
Click on the 30 days tab. A table will appear. Use that table and the map to answer the following questions. You can sort the data by simply click on the arrows on the header line of the table
- Distribution and magnitude of recent earthquakes
2. - Where did the 5 largest earthquakes by magnitude occur during the past month? Are they related to plate boundaries? Which type? You can find that out by comparing the map of each earthquake by clicking on the LOCATION tab. A map of the area will appear with the distribution of the strongest earthquakes located in the area. Make sure that on the right side menu the tab “show plate boundary” is on.
Fill the table below, ranking the earthquakes from the strongest to the least strong.
LOCATION Date Magnitude Depth (km) Tectonic setting/ Type of plate boundary Rank
1
2
3
4
5
- To have an appreciation of the energy associated with the strongest earthquake in this set, go to: http://earthalabama.com/energy.htm Enter the magnitude and then click on the tab “compute”.
What is the energy in Joules traveling by seismic waves? __
Look at the table “calculated seismic energy”. If earthquake energy could be harnessed, for how long could that earthquake power the US? For how many years could that power the average USA household? ___
Part 3: Earthquake Intensity and Secondary Earthquake Hazards case studies
Introduction
The main hazard related to an earthquake is the ground shaking, however, earthquakes poses several other hazards that can have longer lasting and more devastating effects on the natural environment and human interests. These are called secondary seismic hazards:
• Landslides and soil liquefaction
• Damage to structures and infrastructures; buildings can collapse, trapping people inside and burying streets in rubble. Damaged roads, rails, bridges can disrupt or cut off entire communities and hinder rescue efforts
• Fires and loss of lifelines from damage to utilities lines
• Tsunami, which present the greatest hazard at coastline communities.
• Permanent ground deformation
• Loss of life and societal disruption. They can severely hinder economy and societal frameworks.
The size of these secondary hazards depends on the earthquake strength and duration, on the local geological conditions and on the type of structures and society preparedness.
In the following exercise, you will evaluate the differences between measurements of intensity and magnitude and their relationship to secondary seismic hazards for case studies of historical earthquakes.
Read the material for each case study and answer the questions. For an in depth study click on the links to access the main source of info. Based on the description, estimate the intensity of the earthquake main shake using the Modified Mercalli Intensity scale on next page.
Mercalli Modified Intensity Scale
Sample Solution