Earthquakes and Plate Tectonics Our Violent Earth

The Earth’s Changing Crust ► Todays evidence: EQ’s, volcanic eruptions, mountain growth, moving landmasses. ► Past movements based on the concept of ORIGINAL HORIZONTALITY: Assumes that sed. Rocks and some extrusive igneous. Rock form in horizontal layers parallel to the earths surface.

Past evidence of crustal movement ► Deformed rock layers such as folded rock, faulted rock, tilted rock, uplifted rock (with displaced fossils.) See page 214 of book.

Crustal Change in depth Crustal Change in depth ► Folds: bends in crust caused by compressional stresses  Anticlines: up-turned folds: Hills  Synclines: down-turned folds: valley  Tilts are just eroded sections of the above. ► Faults: Breaks in the crust where movement occurs  Normal: hanging wall moves down  Reverse: hanging wall moves upward  Strike-slip: one block slides past the other laterally ► Mountains (uplift): up-thrust crust material at high elevation

Earthquakes ► The natural, rapid shaking of the lithosphere caused by release of energy stored in rocks ► Most earthquakes are caused by: FAULTING  The grinding of pieces of crust past one another ► Some are causes by the movement of magma within the lithosphere under volcanoes

Earthquake Terminology ► Seismic Waves:  The shock waves of a quake ► P-Waves:  Primary waves; fastest wave, first to be recorded; particles vibrate in the direction of movement, like a sound wave; travel through solids and liquids ► S-Waves:  Secondary waves; second to be recorded; particles vibrate at right angles to the direction of movement, like a water wave; travel through solids only ► Focus:   Point below earth’s surface where the energy is released ► Epicenter:  Point on earth’s surface above the focus; most damage is done here

Why Study Earthquakes ► Develop an “early warning” or “prediction system” ► Seismic waves give scientists information on the inner layers and composition of the Earth  Different materials allow seismic waves to act differently

VELOCITY OF SEISMIC WAVES ► Velocity depends on the material they are passing through a. Increase density and pressure – greater the velocity b. Waves are refracted or bent as waves pass through material with different densities

EARTHQUAKE SHADOW ZONES ► At an angle of 103° (distance 11,000 kms) from the epicenter both P and S waves disappear ► P waves can again be detected at l42° (16,000 kms.) NO S WAVES EVER APPEAR AGAIN NO S WAVES EVER APPEAR AGAIN ► THIS BAND OF 39° IN WHICH NO WAVE ARE OBSERVED IS CALLED THE EARTHQUAKE’S SHADOW ZONE

EARTHQUAKE SHADOW ZONES P WAVES DISAPPEAR FROM 105º -140º S WAVES DISAPPEAR FROM 105º NEVER TO APPEAR AGAIN

ANALYSIS OF SEISMIC WAVES HAVE RESULTED IN THE INFERENCE ABOUT EARTH’S INTERIOR S WAVES CANNOT PASS THROUGH THE LIQUID OUTER CORE

Earthquake Magnitude ► The strength of an earthquake ► Measured on an intensity scale ► Ex: Richter Scale Seismograph needle and readout; shows P and S Waves being recorded

Earthquake Magnitude Scale Japanese Magnitude Scale from 0 - 7

Seismograph March 28, 2005, near Northern Sumatra, Indonesia. This 8.7 magnitude earthquake came only three months after the devastating magnitude 9.0 earthquake of December 26, 2004, which caused the Tsunami. Traditional Mechanical Seismograph

Locating the Epicenter of an Earthquake (Steps) 1. Acquire P and S wave data from at least 3 monitoring stations. 2. Calculate the difference in arrival times between the P and S waves for each station. 3. Use your reference tables to determine the distance that station is from the epicenter. 4. Strike a circle with the scaled diameter of the distance you just calculated. 5. Do this 2 more times; where all 3 meet is the location of the epicenter.

LOCATING EARTHQUAKE EPICENTER LOCATING EARTHQUAKE EPICENTER MUST HAVE DISTANCE FROM 3 SEISMOGRAPH STATIONS TO DETERMINE EPICENTER

Practice Using the P and S wave Arrival Time Chart 1. If the P wave arrived at 02:00:00 and the S wave arrived at 02:04:00, find the distance the station is from the epicenter. 2. If the P wave arrived at 12:12:00 and the S wave arrived at 12:24:30, find the distance the station is from the epicenter. 3. If the P wave arrived at 09:15:30 and the S wave arrived at 09:18:50, find the distance to the station.

Practice Using the P and S wave Arrival Time Chart 4. If a monitoring station were 8200 km from the epicenter of an earthquake. If the P- wave arrived at 2:15 PM, find the time the earthquake occurred. 5. If a seismic station was 2600 km from the epicenter of a quake and it recorded an S- wave at 1:00 PM, find the time the quake occurred.

Practice Using the P and S wave Arrival Time Chart 6. If an earthquake occurred at exactly 7hr: 45 min: 00 sec. and the p-wave arrived at a station at 7 hr: 52 min: 00 sec, when did the s-wave arrive? 7. An earthquake exactly 8000 km away from a station occurred at 3 hr: 03 min: 00 sec. When did the P-waves arrive? When did the S-waves arrive?

NORMAL FAULT REVERSE FAULT TRANSFORM FAULT

Plate Tectonics ► The theory that suggests Earth’s lithosphere is broken up into sections (lithospheric plates or tectonic plates) and their movement and interactions produce major changes in Earth’s surface ► At the plate boundaries you’ll find: Earthquakes, volcanoes, trenches, mountains and mid-ocean ridges-Zones of frequent crustal activity!!! Ex: Pacific Ring of Fire

Sea-Floor Spreading ► Brand new ocean crust (basalt) is being made and is spreading out from the ridge. ► Evidence: ► Alternating zones of reversed magnetic polarity at equal distances from the ridge. ► The age of the basaltic rock gets older at equal distances from the ridge.

Continental Drift ► The movement of continents with respect to one another. ► Evidence: ► “Jig Saw Puzzle Effect” ► Similarities of rocks, minerals, fossils and age at continental margins. ► Some mountain chains line up when the continents are put back together.

Driving Force Behind Plate Tectonics ► Convection Currents in the mantle of Earth ► Convection currents work like tank tracks and cause the plates to move by slowly dragging them around Earth’s surface

Earth’s Surface over time ► Reference tables: page 9; right column ► The Location of the North America has changed throughout geologic history ► The continents have been connected 2 times throughout geologic time and have subsequently broken up due to plate movements ► If this process continues, we will be part of a new super-continent in another 250 million years

Plate Boundaries ► Divergent Plate Boundaries: Crustal plates move apart (Ex. Mid-ocean Ridge)

Plate Boundaries ► Convergent Boundaries: crustal plates move toward each other; cause collisions ► Ex. Ocean Trench

Plate Boundaries ► Transform Boundaries: one plate slips past another with no vertical motion; San Andreas Fault, California

NORTH WEST SOUTH EAST SAN ANDREAS FAULT PACIFIC PLATE WEST SIDE MOVES NORTH NORTH AMERICAN PLATE EAST SIDE MOVES SOUTH

Test Review ► Test is coming!!! ► Castle Learning Review ► Earthquakes and Plate Tectonics Review ► Will help out with the upcoming test