Monitoring Earthquakes Section 2-3

Seismograph Seismic waves cause drum to vibrate Pen moves very little and records drums vibrations Study arrival of P, S and surface waves on seismogram Height of lines is greater for an earthquake close to the seismograph

Monitoring Faults Developed instruments to measure changes in: elevation tilting of land surface ground movements along faults

Tiltmeter Measures tilting or raising of the ground Like a carpenter’s level Consists of two bulbs that are filled with liquid and connected by hollow stem As the land rises or falls slightly, the liquid flows from one bulb to the other Read scales to measure amount of tilting

Creep meter Uses a wire stretched across a fault to measure horizontal movement of the ground Wire is attached to a weight that can slide if fault moves

Laser ranging device Uses laser beam to detect horizontal fault movements Time laser beam as it travels from reflector back

GPS Satellites Monitors changes in elevation and horizontal movement along faults Measures tiny movements of markers set up on opposite sides of faults

Mapping Faults Detect seismic waves that reflect off of a fault Helps map fault’s length and depth Helps determine earthquake risk in an area

Earthquake risk in U.S.

Monitoring Changes along Faults How rocks move along a fault depends on how much friction there is between the sides of the fault When friction is low, rocks slide past without much sticking; earthquakes are unlikely Where friction is moderate, sides of fault jam together; produce small earthquakes Where friction is high, rocks lock together; stress builds up until an earthquake occurs

Trying to Predict Earthquakes Even with data from many sources, geologists can’t predict when and where a quake will strike Predicting earthquakes is one of the many scientific questions that remain unsolved!