EQ Monitoring and Hazards NOTES.notebook. January 07, P-wave. S-wave. surface waves. distance

Transcription

1 Earthquake Monitoring and Hazards Reading a Seismogram General guidelines: P-wave First disruption of trace = Second disruption of trace = surface waves Largest disruption of trace = Not the distance to the Epicenter distance To find the distance: 1. Difference in P and arrival times. 2. Use the "slip and slide" method on page 11 of the ESRT to determine the distance. distance 3 2. Use a drawing compass to make a circle around each station s location to their respective from the 1

2 2. Use a drawing compass to make a circle around each station s equal location to their respective epicenter from the distances 3. All three circles will at one common intersect point the 3. All three circles will at one common intersect epicenter point the Note: Often, the three circles don t exactly. close overlap "triangle" Instead they come and form a. EPICENTER In this case the epicenter is assumed to be "triangle" in the. centered 2

3 Almost everything known about the structure of the Earth is based on inferences made from the analysis of waves. seismic Seismograms help seismologists determine: travel 1. Wave travel 2. Wave speed 3. Wave refraction times distances bending 4. Wave ( ) With this information, the and of Earth s internal layers can be estimated. composition density By monitoring activity, seismologists have determined that the outer core is and the other solid layers are because only travel solids through. Seismograph stations on the opposite side of the world from the focus record only and not. liquid P-waves It is also known that materials of different refract bend densities can or waves. differences result in where no wave activity is monitored due to No wave. 3

4 It is also known that materials of different refract bend densities can or waves. Both S & P waves Both S & P waves Density differences result in zones where no wave activity is monitored due to refraction wave. shadow "shadow zone" "shadow zone" P-waves only ic.mov Factors Affecting Wave Travel Substance and Waves travel through more solid density faster ( ) substances Waves shake more violently ( ) softer through substances hardness dense higher amplitudes Earthquake Risks earthquake Aftershock: an that occurs after a larger earthquake in the same area. hours days months May strike,, or later. collapse Can result in of structures previously weakened by primary earthquake. Liquefaction: Violent shaking suddenly turns loose, soft, moist liquid soil into. sinkholes mud landslides Results in and Earthquake Risks Tsunamis: Earthquake can jolt the causing it to rise slightly and water. low ocean push Originally creates very waves with almost floor 60 miles between each wave; however, as they approach waters near land, bunch shallow waves and form a mountain of water over 60 feet tall. up 4

5 Earthquake Precautions Don t build homes: faults Near or on slopes Near or on filled land Near or on Earthquake Monitoring Most earthquakes strike without warning; however, geologists use instruments to measure and deformation of the crust in attempts to predict a pending earthquake event by monitoring horizontal vertical stress and movements along known faults. Earthquake Monitoring Creep Meters: Wire stretched across a fault to measure amount of horizontal movement Laser Ranging Devices: Uses a laser beam on one side of the fault and a detector on the other to detect even fine movements Satellite Monitors: Satellites equipped with radar to bounce radio waves off the ground and to receive their echo to determine vertical movement 5