Earthquakes

What is an Earthquake? Earthquake--Occur when rocks under stress shift along a fault (energy released) Fault—break in rock where one block moves relative to another

Let’s Build a Fault Model!

Damage from Northridge Earthquake in Southern California--1994

Anatomy of an Earthquake Focus--1st motion of earthquake in Earth, along fault Epicenter—point on Earth’s surface directly above focus 90% of continental earthquakes have shallow focus—most damaging

Parts of an Earthquake

Elastic Rebound Elastic Rebound —sudden return of deformed rock to undeformed shape Elastic rebound causes earthquakes

Fence offset due to Elastic Rebound

Seismic Waves When rocks on a fault move, they release energy as seismic waves Seismic waves travel outward from the focus in all directions

Body wave—seismic wave that travels thru a medium two types: P-wave & S-wave

Seismic Waves P (primary) waves are the fastest & travel thru solids, liquids, & gases

Seismic Waves S (secondary) waves are 2nd fastest & travel thru solids only. Although slower they can cause the most damage

Seismic Waves Surface wave— a seismic wave that travels along surface of medium. These are S & P waves that reach the surface & can cause greatest damage

Water Wave and Slinky Activities!

WAYS TO MEASURE AN EARTHQUAKE There are two major scales to measure an earthquake: Mercalli Scale: measures earthquake intensity (by amount of damage caused) Richter Scale: measures earthquake magnitude (strength)

Studying Earthquakes Seismology— study of earthquakes & seismic waves Seismograph— records vibrations in ground Seismogram— tracing of EQ motion, recorded by seismograph

Bill Nye on the Richter Scale http://www. youtube. com/watch Bill Nye on the Richter Scale http://www.youtube.com/watch?v=1qbg7orb1lc Bill Nye on Waves Earthquake recording station/seismograph clip http://www.youtube.com/watch?v=dx4OqT0PYnU&lr=1

SEISMOGRAM Order of recording: P-waves, S- waves, then surface waves Shows S-P lag time

P-Wave S-Wave S-Wave P-Wave S-Wave P-Wave To find S-P lag time, subtract where the P wave starts from where the S wave starts (S-P = Lag Time)

What is S-P lag time for San Francisco, CA? What is S-P lag time for El Paso,TX? 28 sec – 0 sec = 28 sec lag time What is S-P lag time for San Francisco, CA? 120 sec – 0 sec = 120 sec lag time What is S-P lag time for Seattle, WA? 165 sec – 0 sec = 165 sec lag time Which city is closest to the epicenter? The city with the shortest lag time is closest to the epicenter, so it’s El Paso, TX

Locating Earthquakes Through Triangulation S-P lag times are analyzed to find the epicenter of Earthquakes using 3 stations Why 3 stations? Because all we know is distance, so it takes 3 circles to narrow it down to one point Epicenter

Let’s stop here and practice finding S P lag time

Fault Zones Fault zone —region w/ lots of faults that typically form at plate boundaries Fault zones and earthquakes can occur away from plate boundaries as well

Fault Zones—New Madrid New Madrid fault line—New Madrid, MO—120 miles southward on I-55 1811/1812—most widely felt series of E.Q. in U.S. history (2000+) Five were 8.0+ Ancient fault zone deep in crust of Mississippi River region

Tsunamis Tsunami—giant ocean wave that forms after volcanic eruption, submarine earthquake or landslide May form when ocean floor rises due to earthquake Tsunami animation http://embc.gov.bc.ca/em/tsunamis/causes_2.htm

Japan’s Tsunami Before and After…(Google Earth)