-relatively smaller earthquakes occurring in vicinity of main shock- currently not useful for earthquake prediction o Aftershock - smaller shocks that follow main shock and distributed throughout fault plane o Damage - generally greatest damage near epicenter, but other factors may influence this e.g. ground type or bedrock o Seismographs -measures magnitude of vertical and horizontal motion related to earthquakes o Seismograms -records from seismographs Determining the size of an earthquake • 1. A geologist measures the amplitude of the largest seismic wave (23mm • 2. the time interval between the P-wave and S-wave arrivals (24 s) to determine the distance from the epicenter to the station (210 km) • 3. By plotting the two measurements on these graphs and connecting the point, the geologist determines the Richter magnitude of the earthquake (5.0)
• Richter scale - logarithmic (i.e. each unit represents 10x more ground motion than the previous one) or a factor of 33x more energy). • Another measure of damage-shaking intensity determined by the modified Mercalli Scale • Moment Magnitude (Mw)-determines strain energy released from entire fault surface (total energy released) o Most recent method Patterns of faulting • Earthquakes develop as result of slippage along fault plane •
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- Spring '07
- Geology, Seismic Waves