Kennebec River, Georgetown, ME Vanessa Lyons Sea Caves, La Jolla, CA Samantha Bassman.

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Presentation transcript:

Kennebec River, Georgetown, ME Vanessa Lyons

Sea Caves, La Jolla, CA Samantha Bassman

Montmorency Falls, QC Emily Stuart

EARTHQUAKES SEISMIC WAVES

EARTHQUAKES SEISMIC WAVES BODY WAVES BODY WAVES transmit energy through the Earth’s interior in all directions from the earthquake’s focus.

EARTHQUAKES SEISMIC WAVES BODY WAVES Are the fastest seismic waves (6-7 km/sec). First to arrive at earthquake station and be recorded on a seismograph. Energy is a compressional wave that alternates between compression and dilation. Vibration is parallel to direction of travel. Produces sharp jolts. PRIMARY or P-WAVES

EARTHQUAKES SEISMIC WAVES BODY WAVES Slower than P-waves (3.5 km/sec). Second wave to arrive at earthquake station and be recorded on a seismograph. Energy is up and down movement. Vibration is perpendicular to direction of travel. Produce continuous wriggling motion. Do not travel through liquid. SECONDARY or S-WAVES

EARTHQUAKES SEISMIC WAVES SURFACE WAVES Transmit energy along Earth’s surface. Causes the Earth’s surface to vibrate. Slowest of the seismic waves (2.5 km/sec). Two types:side to side whipping action rolling up and down (i.e. ocean wave) Both can occur at the same time. Causes extensive damage to rigid structures.

EARTHQUAKES SEISMIC WAVES SURFACE WAVES

EARTHQUAKES MEASURING EARTHQUAKES MODIFIED MERCALLI INTENSITY SCALE Earthquake strength depends on how much stored energy is released or INTENSITY. Initially looked at destructiveness of earthquake. Can’t locate the epicenter accurately or measure distance and actual intensity. Doesn’t consider quality of building vs. intensity. Can’t be used where no people live. Good to characterize historical earthquakes. Introduces a human component to earthquakes.

EARTHQUAKES MEASURING EARTHQUAKES

EARTHQUAKES MEASURING EARTHQUAKES RICHTER SCALE Scale is based on MAGNITUDE, which is the amount of energy released by the earthquake. Magnitude is the amplitude of the largest peak on the seismogram. Really designed for use only in California. Works best for earthquakes of magnitude 7 or less.

The Richter scale is logarithmic, that is an increase of 1 magnitude unit represents a factor of ten times in amplitude. The seismic waves of a magnitude 6 earthquake are 10 times greater in amplitude than those of a magnitude 5 earthquake. However, in terms of energy release, a magnitude 6 earthquake is about 31X greater than a magnitude 5 and ~1000X greater than a 4.

EARTHQUAKES MEASURING EARTHQUAKES

EARTHQUAKES MEASURING EARTHQUAKES MOMENT-MAGNITUDE SCALE Seismic moment more accurately gauges the total energy of a large earthquake. MOMENT = (total length of fault rupture) X (depth of fault rupture) X (total amount of slip along rupture) X (strength of rock) Produces MOMENT-MAGNITUDE scale. The longer the fault, the greater the earthquake. Allows direct measurement of quake related to its cause.

EARTHQUAKES EARTHQUAKE DEPTH AND MAGNITUDE DEPTH Related to depth of focus of the earthquake. Shallow focus = < 70 km (< 45 miles) Intermediate focus= km ( mi.) Deep focus= > 300 km (> 180 miles) 90% of all earthquakes have a focus < 100 km. Most occur within 60 km (40 mi) of Earth’s surface. Heat weakens rock with depth and rock loses its ability to store strain energy.

EARTHQUAKES EARTHQUAKE DEPTH AND MAGNITUDE DEPTH Focus closer to surface allows greater brittle failure Good Friday Alaskan quakeD = 33 km 1994 Northridge, CA quakeD = 21 km 1989 Loma Prieta, CA quakeD = 18 km

EARTHQUAKES EARTHQUAKE DEPTH AND MAGNITUDE MAGNITUDE Generally, earthquakes with shallower foci have greater magnitude. (Magnitude is the amount of energy released by the earthquake.)

EARTHQUAKES EFFECTS OF EARTHQUAKES GROUND DISPLACEMENT Most obvious geologic effect of earthquakes San Francisco 1906 earthquake had 7 m of horizontal displacement. Anchorage 1964 Good Friday earthquake had land going up 12 m and sea floor down 16 m. Anchorage earthquake was second largest ever recorded.

EARTHQUAKES EFFECTS OF EARTHQUAKES GROUND DISPLACEMENT 1964 Anchorage Earthquake 1906 San Francisco Earthquake

EARTHQUAKES EFFECTS OF EARTHQUAKES LANDSLIDES AND LIQUEFACTION Shaking and tremors dislodge unstable masses of rocks and soil on hillsides. Fragments can be dislodged from bedrock and buildings as well.

EARTHQUAKES EFFECTS OF EARTHQUAKES LANDSLIDES 1959 earthquake at Hebgen Lake, MT 1995 landslide in La Conchita, CA

EARTHQUAKES EFFECTS OF EARTHQUAKES FALLING DEBRIS

EARTHQUAKES EFFECTS OF EARTHQUAKES LIQUEFACTION Conversion of unconsolidated material with some initial cohesiveness in to a mass of water-saturated sediment that flows like a liquid, although no water has been added. Shaking increases the pressure on the water between the sediment grains, forcing them apart Loss of frictional contact produces a slurry of sediment and mud

EARTHQUAKES EFFECTS OF EARTHQUAKES LIQUEFACTION Turnagain Heights, AK 1964 Government Hill Elementary School Anchorage, AK, 1964

EARTHQUAKES EFFECTS OF EARTHQUAKES LIQUEFACTION Kobe, Japan

EARTHQUAKES EFFECTS OF EARTHQUAKES LIQUEFACTION Kobe, Japan

EARTHQUAKES EFFECTS OF EARTHQUAKES LIQUEFACTION Port Royal, Jamaica 1692 City slid 15 m below sea level.