7.3 Measuring and Predicting Earthquakes The Way Tectonic Plates Move

Learning Targets: Locate earthquakes – epicenter and focal point Explain how the release of energy of various types of earthquakes relates to magnitude, P and S waves Predict the locations of earthquakes and faults (strike- slip, reverse and normal) based on soil, geological, or topographical maps. Relate fault locations/types to plate boundaries Explain precautions that can be made to protect life from earthquakes

Measuring Earthquakes Seismometer: detects and records seismic waves Must be firmly attached to the ground Why? A device used to measure seismic waves is called a seismometer. Look at the Root word List 4.

Seismometers Three seismometers needed to measure all the shaking 1 for vertical movement 2 for horizontal movement in perpendicular orientations Rolling waves compared to side to side waves

Horizontal

Verticle

Seismograms Seismogram: written record of an earthquake Read from left to right Order of arrival always the same P-waves S-waves Surface waves

Seismograms Seismograms calculate Location of epicenter Magnitude (strong) Data from hundreds of stations is compared for added precision and accuracy

Locating the Epicenter Each seismogram can tell the distance to the epicenter But direction is uncertain How many seismograms does it take to find the epicenter? Three seismograms can give exact location

Locating the Epicenter P-waves and S-waves travel at known speeds Difference in arrival times shows how far away the earthquake was

Earliest time is left, later time is right

How many seismograms are needed in order to pinpoint the epicenter of an earthquake? 3

Calculating Magnitude Magnitude: energy released by an earthquake Based on the amplitude of the seismogram and distance from the epicenter Skip slide

Intensity vs. Magnitude Intensity: amount of shaking and damage Differs from place to place depending on soil type and population density Magnitude: amount of energy released by an earthquake Helps compare earthquakes Not useful in determining damage or death toll The amount of shaking and damage done by an earthquake is the intensity. The amount of energy released by an earthquake is called the magnitude.

Mercalli Scale Ranges from I-XII (1-12) Intensity (not magnitude) Good Reports actual damage done Very practical for risk assessment Bad Subjective Differs from place to place e.g. Chile/Haiti Intensity is the amount of shaking and damage done during an earthquake.

Magnitude Scales Richter Scale: energy released in a single point Moment magnitude: energy released along entire fault The total energy released by an earthquake along its entire fault is measured on the moment magnitude scale.

How magnitude and distance is calculated.

Large Spike Far Small Spike Near

Magnitude Scales Moment magnitude is the modern scale Similar to Richter, but measures power and size of fault

Earthquake Prediction Easy to predict where Hard to predict when and what magnitude (or how strong) Which of the following are seismologists successfully able to predict? Where an earthquake is likely to occur.

Earthquake Prediction Long term risk factors Along plate boundaries Seismic Gap: moved less than rest of fault Short term risk factors Foreshocks Ground tilting Unknown When Many small quakes or one large quake Long and short term risk factors for living in that area. Why are there usually no evacuations right before an earthquake? Nobody knows when an earthquake is going to occur so there is no time for evacuation.

Seismic Gap A seismic gap is a section of a fault that has produced earthquakes in the past but is now quiet. For some seismic gaps, no earthquakes have been observed historically, but it is believed that the fault segment is capable of producing earthquakes on some other basis, such as plate-motion information or strain measurements

7.4 Staying Safe In earthquakes

Long Term Earthquake Safety Buildings can be built to move independently of the ground Masonry can be reinforced with steal Soft soils can be left to low density development Emergency plans can be made Monitoring and warning systems put in place

Short Term Earthquake Safety Gas companies and mass transit systems can benefit from a few seconds warning Beaches cleared before tsunami impact People take shelter

Global Seismic Risk