Magnitude verses Intensity! Earthquake Strength Magnitude verses Intensity!

Magnitude Is a measure of the amount of energy released from an earth quake. Recorded by the amplitude of the highest S wave There is only one magnitude for each earthquake – but we still use 3 seismograms to calculate it Magnitude of earthquakes is measured by the Richter scale or Moment Magnitude

Richter scale – developed by Charles Richter in 1930

31.7 times more energy released and 10 times stronger for every unit increase on the Richter scale

How is this magnitude calculated?

Moment Magnitude The measure of total energy released by an earthquake Preferred by seismologists because it is more precise Based on the area of the fault ruptured in the quake instead of just the epicenter Calculated by multiplying the area of the fault’s rupture surface by the distance the earth moves along the fault www.scsn.org/magnitude.html

Earthquake Intensity A number describing the severity of an earthquake in terms of it’s effects on the earth’s surface, human beings, and structures such as buildings – Basically the impact the earthquake causes! Measured by the Mercalli Scale

Mercalli Scale

The Mercalli scale helps create “Isoseismic Maps”

Maps that shows how often and how strong

Can we predict Earthquakes?

Warning Signs Average temperature of the area keeps increasing – a few months prior to an earthquake A sudden rise or fall in water levels Seismo-electromagnetic precursor – (10-20 hours prior) geomagnetic field is reduced which affects radio, tv, telephone, and cell phones Animals highly disturbed and restless Sensitive patients may experience an increase in blood pressure, migranes, heart trouble

Seismic gaps A zone along a tectonically active area where no earthquakes have occurred recently, but it is known that elastic strain is building in the rocks If identified it might be an area expected to have a large earthquake in the future

Seismic Gap In this illustration you can see areas of earthquake activity and an area of non activity – the area of non activity represents a “seismic gap” Notice this is a subduction zone between two tectonic plates.

The Gap Hypothesis Parts of active faults that have had relatively few earthquakes are likely to be the sites of strong earthquakes!

San francisco Bay Area A major seismic gap area of interest to scientists in the United States

Assignment Mercalli Scale/isoseismic map activity