Scales and Forecasting Earthquakes Scales and Forecasting

Reverse Fault Compression force – Convergent boundaries Pushes on rocks causing to bend and sometimes break Rocks above fault are forced up and over rocks below fault line Rocky Mountains

Strike-slip Fault (Transform) Shear Force No upward or down movement Surfaces snag and rocks are twisted and strained due to friction Short and sudden but can be slow and steady San Andreas Fault

Magnitude & Intensity Damage caused by Earthquakes depends on… Distance to Epicenter Depth of Focus –How far underground the earthquake occurs. Bedrock/Soil Types # and types of structures located in the area

Magnitude vs. Intensity – measured force based on seismic waves that travel through the earth Measurable Intensity – What was felt? -What occurred? Observer specific

Modified Mercalli Scale Arbitrary set of definitions based upon… What people in area feel when earthquake occurs - Deals with the Intensity Their Observations of damage to buildings Example: Is the chimney broken? Did the chimney totally fall over? Where the windows shattered? The scale is 1 to 12

Advantages Mercalli Scale Great for use if happens in an inhabited area of developed country. (lots of people can describe damages) Easy to use Do not have to use specific equipment

Disadvantages of Mercalli Scale No use in middle of desert or places without buildings and tree. Observer specific – what appears to be “heavy” to one person may not be considered heavy for another.

Richter Magnitude Scale Is the effects of any one earthquake varies greatly from place to place May be many intensity values (e.g. IV or VII) measured for same E-Q Each E-Q should have only one magnitude (e.g. 4.5 on the Richter scale) Based on seismic waves travel through Earth Deals mainly with the strength of the break, How much energy is released by the E-Q Tool to get an idea, Not Perfect

Richter Magnitude Scale Allow us to compare earthquake magnitudes regardless of location Good for small, nearby earthquakes Used from 1930’s to 1980’s It is logarithmic – metrics is comparable Meaning that each whole number step represents a ten-fold increase in measured amplitude. For example a magnitude of 7 E-Q is 10 times larger than a 6, and 100 times larger than a 5, and 1000 times larger than a 4. With each increase of 1.0 , the energy release increases by 32 times.

Moment Magnitude Scale Estimates the total energy released by earthquake Good for all earthquakes Measures size and type of waves and movement along faults Movement gives us more information When you hear “Richter” on the news, actually referring to Moment Magnitude Scale

Forecasting vs. Predicting Forecasting – General statement about what will happen in future (not specific) Forcast something will happen in the future (not specific) We have the ability to forecast Predicting – Specific statement with specific date We do not have the ability to predict E-Q Animal behavior – ground animals come out of ground Radon Levels increase in ground water

Why are they so difficult to predict? Many factors Movement – don’t know when Stresses Rock mechanical property (brittle of elastic Past movement – No History Seismic gaps