Learning objectives Understand the relationship of earthquakes to faulting Familiarization with earthquake & wave (energy) terminology Understand the concept of earthquake magnitude (and its calculation) How seismic risk is estimated Familiarization with the major effects of earthquakes The prediction of earthquakes Mitigation of earthquake damage

Earthquake Processes Earthquakes: Occur predominately at plate boundaries Mainly in conjunction with faults Due to movement along fault planes Relationship to plate tectonics evidenced by: –Geographic distribution & correlation with plate boundaries –Relationship to plate boundaries Shallow earthquakes (at both divergent and convergent boundaries) Deep earthquakes (at convergent boundaries; subduction zones)

Earthquake Terminology Seismic (seismicity): (earth) movement/shaking relating to earthquake (also artificial) vibration/activity Focus: Actual (centered) area of movement on the fault plane (where the rupture starts) Epicenter: Point on the earth’s surface directly above the focus (apparent focal point) (more later)

Map of world-wide seismicity

Major Earthquake Belts

Types of Plate Boundaries & Seismicity Divergent-Margin Earthquakes Convergent-Margin Earthquakes Transform-Margin Earthquakes Intraplate Earthquakes –Basin and Range; Mid-Continent

Dip-Slip normal reverse (thrust) Strike-Slip Left Lateral Right Lateral

Mid-Continent Faulting/Seismicity: Basin-Range Type

Fault-Related Landforms + Wine glass valleys

Fault Activity

Slip Rate & Recurrence Interval Slip Rate: Rate of displacement per year (units of e.g., mm/yr; 1m/1000 yrs = 1 mm/yr) Recurrence Interval: based on –Seismicity: Historical time interval between events –Paleoseismic data: Time interval between events from the geologic record –Recurrence Interval; displacement/event  slip rate e.g., 1m  2mm/yr = 500 yr interval

Seismic Waves and Ground Shaking Types of seismic waves –Body waves: waves travel within the earth P- waves: Primary compression waves S- waves: Shear waves –Surface waves: waves that travel only along/within surface layers (shallow) L-(Love) waves: horizontal ground movement Rayleigh waves: rolling motion Focus: Point/area where rupture starts Epicenter: point on earth’s surface directly above the focus

Waves=Forms of energy release Motion/propagation types Frequency: Number of waves passing a reference point/sec (in Hz) Period: Number of seconds between successive peaks Amplitude: Measure of ground motion Attenuation/amplification Seismic Waves

Nature & Propagation of Seismic Waves Waves travel at different rates, & depend on: –intrinsic velocities P-waves:  5.5 km/sec S-waves:  3 km/sec (cannot propogate through liquids) –rock material type (density); denser  faster; less amplification –refraction –reflection

Comparing/Measuring Earthquakes Magnitude –Measure of energy released (log scale) –measurement scale = Richter scale (0-10) Intensity: –Relative scale: based on perceived damage –Modified Mercalli Scale (1-12) Ground acceleration during earthquakes –Rate of change of horizontal or vertical velocity of the ground –Normalized/compared to earth’s gravity; 9.8 m/sec 2 = 1g –e.g., M = quake  g

M easurement Methods: Seismometers Horizontal Motion Vertical Motion

Seismograms

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Calculation of Magnitude & Location of Epicenter P-waves: 5.5 km/sec S-waves: 3 km/sec