Earth Science Physical Geology Earthquakes Chapter 6 Notes 2

Earthquakes Focus: Focus: Spot on fault plane where movement first occurs Spot on fault plane where movement first occurs Epicenter: Epicenter: Point on the earth’s surface directly above the focus; often the spot of most devastation Point on the earth’s surface directly above the focus; often the spot of most devastation Seismic wave radiate outward from the focus in all directions Seismic wave radiate outward from the focus in all directions

Earthquakes Shallow focus: Shallow focus: 90% of earthquakes 90% of earthquakes Occur within 70 km of the surface Occur within 70 km of the surface Most destructive Most destructive Intermediate focus: Intermediate focus: Occur between 70 and 300 km Occur between 70 and 300 km Deep focus: Deep focus: Occur between 300 and 650 km Occur between 300 and 650 km Occur farther inland in a subduction zone than any other focus Occur farther inland in a subduction zone than any other focus

Major Earthquake Zones Most earthquakes occur at plate boundaries Most earthquakes occur at plate boundaries Three major zones: Three major zones: Pacific Ring of Fire Pacific Ring of Fire Subduction and transform (shearing) Subduction and transform (shearing) Mid-Ocean Ridges Mid-Ocean Ridges Tension or divergent Tension or divergent Eurasian-Melanesian Belt Eurasian-Melanesian Belt Convergent Convergent

Recording Earthquakes Seismograph: Seismograph: Instrument used to detect and record seismic waves Instrument used to detect and record seismic waves Has three sensing devices: Has three sensing devices: Vertical movement Vertical movement East-west direction East-west direction North-south direction North-south direction Traces wave-shaped lines on paper, a computer or magnetic tape Traces wave-shaped lines on paper, a computer or magnetic tape

Types of Seismic Waves P waves: (primary waves) P waves: (primary waves) Fastest moving waves; First recorded by a seismographs Fastest moving waves; First recorded by a seismographs Travel through solids and liquids Travel through solids and liquids The more rigid the material, the faster the wave moves The more rigid the material, the faster the wave moves S wave: (secondary waves – shear waves) S wave: (secondary waves – shear waves) Slower than P waves; Second to be recorded Slower than P waves; Second to be recorded Can only travel through solids Can only travel through solids Rock particles move in right angles Rock particles move in right angles

Types of Seismic Waves L wave: (surface waves) L wave: (surface waves) Slowest moving waves Slowest moving waves Only travel on the surface of the earth, not through the interior Only travel on the surface of the earth, not through the interior Cause the surface to rise and fall like an ocean wave Cause the surface to rise and fall like an ocean wave Cause the most destruction during an earthquake Cause the most destruction during an earthquake

Locating an E-quake P waves travel 1.7 time faster than S waves P waves travel 1.7 time faster than S waves If a scientist knows what time the P waves and S waves arrive at a seismograph station, they can determine how far away the epicenter is from that same location. If a scientist knows what time the P waves and S waves arrive at a seismograph station, they can determine how far away the epicenter is from that same location. If P waves and S waves arrive close to the same time, the epicenter is near by. If P waves and S waves arrive close to the same time, the epicenter is near by.

Time Travel Graph

Earthquake Measurement Magnitude: measure of the energy released by an earthquake and the description of ground motion Magnitude: measure of the energy released by an earthquake and the description of ground motion Richter Scale: relates magnitude to the damage; used mostly by reports and non- scientists Richter Scale: relates magnitude to the damage; used mostly by reports and non- scientists

Tsunamis Giant wave created by an earthquake on the ocean floor Giant wave created by an earthquake on the ocean floor Caused by faulting or underwater landslides Caused by faulting or underwater landslides Both causes a sudden drop in ocean floor and displaces a large amount of water Both causes a sudden drop in ocean floor and displaces a large amount of water Creates long, low waves Creates long, low waves

Tsunamis Pacific Tsunamis Warning Center (PTWC) Pacific Tsunamis Warning Center (PTWC) Network of seismograph stations around and the Pacific Ocean Network of seismograph stations around and the Pacific Ocean Issues warnings to areas deemed to be in danger Issues warnings to areas deemed to be in danger Not found in the area where the last tsunamis occurred Not found in the area where the last tsunamis occurred Even if there were stations located there, no way to warn people…no media Even if there were stations located there, no way to warn people…no media