Earthquake Measurement Science Chapter 7, Section 2 Notes Science Chapter 7, Section 2 Notes

Section Vocabulary epicenter: the point on Earth ’ s surface directly above an earthquake ’ s starting point, or focus. The prefix epi- means upon focus: the location within Earth along a fault at which the first motion of an earthquake occurs. (inside Earth) magnitude: a measure of the strength of an earthquake intenstiy:in Earth science, the amount of damage caused by an earthquake epicenter: the point on Earth ’ s surface directly above an earthquake ’ s starting point, or focus. The prefix epi- means upon focus: the location within Earth along a fault at which the first motion of an earthquake occurs. (inside Earth) magnitude: a measure of the strength of an earthquake intenstiy:in Earth science, the amount of damage caused by an earthquake

I. Studying Earthquakes 1. Scientists use earthquake-sensing instruments called seismometers, or seismographs. 2. Record the vibrations of P waves, S waves, and surface waves. 3. Also record the time waves take to arrive at seismometer station. 1. Scientists use earthquake-sensing instruments called seismometers, or seismographs. 2. Record the vibrations of P waves, S waves, and surface waves. 3. Also record the time waves take to arrive at seismometer station.

I. Studying Earthquakes A. Determining Location a. Use data to determine earthquake ’ s epicenter. b. Epicenter is directly above earthquake ’ s starting point. c. Focus is point inside the Earth where the earthquake began. A. Determining Location a. Use data to determine earthquake ’ s epicenter. b. Epicenter is directly above earthquake ’ s starting point. c. Focus is point inside the Earth where the earthquake began.

I. Studying Earthquakes B. Triangulation a. The time between the arrival of the P waves and the S waves is called lag time. b. Epicenter is located by drawing a circle around three seismometer stations and radius of each circle is equal to the distance from the station to the epicenter. c. The point at which all three circles intersect is the epicenter. B. Triangulation a. The time between the arrival of the P waves and the S waves is called lag time. b. Epicenter is located by drawing a circle around three seismometer stations and radius of each circle is equal to the distance from the station to the epicenter. c. The point at which all three circles intersect is the epicenter.

II. Earthquake Magnitude 1.Size of the waves on a seismogram indicates amount of ground motion. 2.The amount of ground motion is used to calculate magnitude. 3.Magnitude measures earthquake ’ s strength. 1.Size of the waves on a seismogram indicates amount of ground motion. 2.The amount of ground motion is used to calculate magnitude. 3.Magnitude measures earthquake ’ s strength.

II. Earthquake Magnitude A.The Richter Scale a.Mainly used in the past to measure magnitude. b.Measures the ground motion from earthquake and adjusts for distance. c.Each increase of a number (ex: 1 to 2) represents a 10-fold increase. d.Values generally range from 0 to 9. A.The Richter Scale a.Mainly used in the past to measure magnitude. b.Measures the ground motion from earthquake and adjusts for distance. c.Each increase of a number (ex: 1 to 2) represents a 10-fold increase. d.Values generally range from 0 to 9.

II. Earthquake Magnitude B. The Moment Magnitude Scale a.Mainly used today to measure instead of Richter scale. b.More accurate measurement of earthquakes. c. Represents the size of the area of the fault that moves, the average distance that the fault blocks move, and the rigidity of the rocks in the fault zone. d.Related to the physical effects that take place. B. The Moment Magnitude Scale a.Mainly used today to measure instead of Richter scale. b.More accurate measurement of earthquakes. c. Represents the size of the area of the fault that moves, the average distance that the fault blocks move, and the rigidity of the rocks in the fault zone. d.Related to the physical effects that take place.

The second map shows the locations of California earthquakes of magnitude 4.5 or greater during a 40-year period.

III. Earthquake Intensity 1. The effects of the earthquake and how it is felt is the intensity of the earthquake. A.The Modified Mercalli Scale a.Used to describe intensity of an earthquake. b.Scale ranges from I (1) to XII (12). c.Level I (1) are barely noticeable. d.Level XII (12) cause total destruction. 1. The effects of the earthquake and how it is felt is the intensity of the earthquake. A.The Modified Mercalli Scale a.Used to describe intensity of an earthquake. b.Scale ranges from I (1) to XII (12). c.Level I (1) are barely noticeable. d.Level XII (12) cause total destruction.

III. Earthquake Intensity B. Mapping Earthquake Intensity a.Show the level of ground shaking expected to occur in different areas that experienced same earthquake. b.Uses data obtained from previous earthquakes. c. Data is used to model differences in amount of ground shaking that may occur in future earthquakes. B. Mapping Earthquake Intensity a.Show the level of ground shaking expected to occur in different areas that experienced same earthquake. b.Uses data obtained from previous earthquakes. c. Data is used to model differences in amount of ground shaking that may occur in future earthquakes.

IV. The Effects of Earthquakes A.Distance from the Epicenter a.As seismic waves move away from an epicenter they grow larger like circles in a pond when a pebble is dropped. b.The total energy in a seismic wave stays constant as the wave travels. c. The amount of energy at a point on the wave decreases as the wave grows larger. This is because the same amount of energy is involved in a larger area (circle). A.Distance from the Epicenter a.As seismic waves move away from an epicenter they grow larger like circles in a pond when a pebble is dropped. b.The total energy in a seismic wave stays constant as the wave travels. c. The amount of energy at a point on the wave decreases as the wave grows larger. This is because the same amount of energy is involved in a larger area (circle).

IV. The Effects of Earthquakes A.Local Geology a.The amount of damage depends on the material the waves travel through. b.Solid rock will not increase the intensity or time that the ground shakes. c. Seismic waves are dangerous when they travel through loose soils and sediments with large amounts of water A.Local Geology a.The amount of damage depends on the material the waves travel through. b.Solid rock will not increase the intensity or time that the ground shakes. c. Seismic waves are dangerous when they travel through loose soils and sediments with large amounts of water

IV. The Effects of Earthquakes d. When water-saturated soil or sediment is shaken by seismic waves, the grains that make up the sediment lose contact with one another and are surrounded by water. This is called liquefaction. e. Liquefaction can intensify ground shaking and also cause the ground to settle. f. Settling can cause structures to tilt or even collapse. d. When water-saturated soil or sediment is shaken by seismic waves, the grains that make up the sediment lose contact with one another and are surrounded by water. This is called liquefaction. e. Liquefaction can intensify ground shaking and also cause the ground to settle. f. Settling can cause structures to tilt or even collapse.

IV. The Effects of Earthquakes A.Earthquake-Resistant Construction a.Structures made of brick or concrete are not flexible. b.They are easily damaged by earthquakes. c.Wood and steel are more flexible. d.Flexible structures are more likely to survive in strong earthquakes. A.Earthquake-Resistant Construction a.Structures made of brick or concrete are not flexible. b.They are easily damaged by earthquakes. c.Wood and steel are more flexible. d.Flexible structures are more likely to survive in strong earthquakes.

IV. The Effects of Earthquakes e.Taller buildings are more susceptible to damage than shorter ones. f.Structures that have solid foundations are firmly anchored to the ground are most likely to be left standing in an earthquake. e.Taller buildings are more susceptible to damage than shorter ones. f.Structures that have solid foundations are firmly anchored to the ground are most likely to be left standing in an earthquake.