SCI 10 Q1 Reviewer - Seismic Waves & Plate Tectonics PDF

LESSON 01: SEISMIC WAVES WAVE - transmits energy from one place to another - elastic and travels through rock - produced by earthquakes or explosions SEISMOLOGY - the study of earthquakes & the nature of earth’s interior (using seismic waves) SEISMOLOGIST...

LESSON 01: SEISMIC WAVES WAVE - transmits energy from one place to another - elastic and travels through rock - produced by earthquakes or explosions SEISMOLOGY - the study of earthquakes & the nature of earth’s interior (using seismic waves) SEISMOLOGIST - also known as earthquake hunters - a person who studies seismic waves in geological material BODY WAVES - travels through the Earth’s interior PRIMARY (P, COMPRESSIONAL, OR LONGITUDINAL) - compresses and dilates - moves parallel to the direction of motion - fastest moving wave - smaller and has a higher frequency - can travel through all 3 states of matter SECONDARY (S, SHEAR, OR TRANSVERSE) - up and down movement - moves perpendicular to the direction of motion - slower than P Waves - can only travel in solid matter SURFACE WAVE - can only travel at the Earth’s surface - arrives after both P & S Waves LOVE WAVE (L, SURFACE, OR LONG) - both velocity and depth are dependant on frequency (dispersive property) (low frequency = greater depth & higher velocity) - parallel to the earth’s surface and perpendicular to the direction of motion - largest at the surface and shrinks with depth RAYLEIGH WAVE (R, SURFACE, LONG, OR GROUND ROLL) - elliptical movement - both perpendicular & parallel to the direction of motion - slightly slower than Love Waves - both velocity and depth are dependant on frequency (dispersive property) (low frequency = greater depth & higher velocity) LESSON 02: LOCATING EPICENTER FOCUS EPICENTER - initial point of an earthquake - point directly above the focus - below the surface - most violent shaking occurs here SEISMOGRAM - data recorded from seismographs SEISMOGRAPH - device used to record the ground’s movement during earthquakes  P1 S1 S1 - P1 See graph P2 S2 P2 - P1 OR below S2 - S1 P-Wave S-Wave Lag Time Epicenter P-Wave S-Wave Origin Arrival Arrival Distance Travel Travel Time Time Time Time Time 08:21:00 08:30:00 09:00 7800 km 11:00 20:00 8:10:00 dashed red line - lag time moved to a gap where it fits red line - used to mark the epicenter distance green line - perpendicular to red line - used to mark the travel time f the p-wave blue line - perpendicular to the dashed red line - used to mark the travel time of the s-wave TRIANGULATION - taking seismographic measurements from at least 3 points - epicenter is where all 3 circles intersect SEISMIC STATIONS - 30 unmanned (1 in both Ormoc & Maasin) - 29 manned (1 in Palo) - 5 seismo-volcanological observatories - Metro Manila micro network (has 5 telemetered stations) - Temporary Hinunangan Network (has 5 stations) LESSON 03: CONTINENTAL DRIFT PANGAEA - a supercontinent that existed around 240 million years ago - composed of two main parts: Laurasia & Gondwana  - surrounded by the Panthalassic Ocean - had a minor body of water called the Tethys Sea FRANCIS BACON (1600s) - had noticed that Africa and South America fit together ANTONIO SNIDER-PELLEGRINI (1858) - enhanced Bacon’s discovery by comparing their coastlines ALFRED WEGENER (1915) - concluded that Africa and South America split due to continental drift CONTINENTAL DRIFT - proposed that continents were once joined together to form Pangaea - rejected due to a lack of a satisfactory mechanism THEORY - Pangaea split into smaller fragments around 200-300 million years ago - these fragments drifted apart to where they are now - less-dense continents moving over denser oceanic crust like icebergs - geologists were highly skeptical and rejected the idea TOPOGRAPHIC EVIDENCE - coastlines of South America & Africa and North America & Europe fit together (believed to have split apart during the Cretaceous Period) - Shelf break on the edges of continents - rock types & sequences are similar and are the same age (500m ~ 2b years old) - mountain ranges line up among the matching coastlines (Appalachian Mountains from U.S. to Scandinavia) - both South America & Africa possess freshwater rock up until the end of the Cretaceous Era where they drifted apart PALEONTOLOGICAL EVIDENCE - Fossils contained within sequences located in different continents - Mesosaurus, a freshwater creature who lived on both land and water, was found in both Brazil and Southern Africa (during Mesozoic Era, around 240 million years ago)  - Glossopteris (fernlike plant), Cynognathus (Early Mesozoic, 230m years ago), and Lystrosaurus (egg-laying land animals who are bad at swimming) are among others - European flora had evolved around 300 million years ago PALEO-CLIMATIC EVIDENCE - distribution of land masses that were covered with ice and tundra 300 million years ago (too far from the south and therefore can no longer have ice) - deposits of rock left by glaciers called Tillites who are the same age were found in Africa, South America, India, and Australia - Coal formed from dead organic matter (plants and animals) were found in Antarctica  - Antarctica was believed to be near the equator and had a lot of organisms - coral and coal found in 280-350 million year old rocks are distributed in regions closer to the north (far from tropical regions where they usually appear) REJECTION OF THE THEORY - does not possess a mechanism - proposed mechanisms were impossible PROPOSED MECHANISMS AND REASONS FOR REJECTION - Tidal energy from the moon and sun (too weak to move continents) - continents plowed through oceanic crust (oceanic crust is too strong) - continents slide over oceanic crust (too much friction) LESSON 04: SEAFLOOR SPREADING PALEOMAGNETISM - direction of magnetism of iron-bearing materials (like magnetite) can determine where a rock is formed with respect to the magnetic pole - rocks with flat magnetic inclination cooled near the equator - scientists discovered that rocks were found in places that did not correspond to their magnetic direction (could either mean the earth’s axis has changed significantly or rocks moved from where they were formed) MID-OCEAN RIDGE (SPREADING CENTER) - longest chain of mountains (84,000km long) in the world - divergent plate boundaries  - rift/upgrowth of the ocean floor caused by rising magma - typical summit elevation of 2,700 meters below sea level - shallowest major feature of the seafloor - oceans are deeper closer to continents SEAFLOOR SPREADING - was proposed by Harry Hess in 1962 - one of the two major processes of plate tectonics (the other being subduction) - creates new crust while subduction destroys old crust (forces balance each other out and the earth’s diameter remains the same) - magma rises to form new crust at ridges -> seafloor crust moves towards trenches and gets subducted back into the mantle (like a conveyor belt) CHARACTERISTICS - young rocks are hotter, less dense, and have less sediments (typically found closer to ridges) - seafloor is lower in areas far from a ridge - magnetic history of the seafloor bears a striped pattern - older rocks are colder, denser, and have more sediments MANTLE CONVECTION - slow, churning motion of Earth’s mantle - currents carry heat from the mantle/core to make the crust more plastic/less dense which causes it to rise (often forms mountains or elevated areas on the seafloor) - cracks in the crust are filled with magma which cools to form igneous rock and becomes a new part of the Earth’s crust - pattern of magnetic stripes PROOF - oldest rock found is 180 million years ago when the earth is far older (4.6 billion) - rocks closer to the ridges were found to be younger than ones that were farther (discovered by the Glomar Challenger, a drilling ship in 1968) - continuous eruptions formed pillow rocks (discovered by Alvin the Submarine)  - RIDGES - Mid-Atlantic Ridge (2-5 cm / 2 inches) -> separates North America from Eurasian | separates South America from Africa - East Pacific Rise (15 cm / 6 inches) -> separates the Pacific from North America, Cocos, Nazca, and Antarctica - Southeast Indian Ridge -> divergent boundary with Antarctica SONAR - bounces sound waves off surfaces and then records the time it takes for it to return (the sooner it returns, the closer the object) - the long mountain ridges were found using this method - longest one was found in the Atlantic Ocean called the Mid Atlantic Ridge (MAR) MAGNETIC FIELD - thought to arise from the movement of liquid iron in the outer core (happens as the planet rotates) - behaves as a permanent magnet near the center of the Earth - rocks stop aligning with the magnetic field at temperatures greater than 585 Celsius (Curie Point) MAGNETIC REVERSAL - where the north pole becomes the south pole and vice versa - used as evidence for seafloor spreading due to a pattern of magnetized stripes - happens every 500,000 years - Normal Polarity -> same as the current one - Reversed Polarity -> opposite to the current one  LESSON 05: PLATE TECTONICS PLATE TECTONICS - umbrella theory that explains the Earth’s activity - creation, movement, contact & flattening of solid rock plates of the lithosphere - idea that the crust and upper mantle are broken into sections (plates) that move around on top of the mantle PLATE - can have both oceanic & continental crust - layer of rock that drifts slowly over the asthenosphere (uppermost layer of the mantle) and is tectonically active - made up of the lithosphere (made up of the crust and upper part of the mantle) - the crust is divided into 15 major plates - motion of these plates cause collisions, divergences, or scraping of boundaries - move at rates less than 1-16cm/year TECTONICS (tektonikos - builder) - describe the formation & movement of oceanic and continental plates - refers to the deformation of the crust as a result of plate interactions PLATE MOVEMENT - move using the hot mantle convection currents - constantly moving (8 inches/year in some areas) (Pacific Plate moves the most) - affected by the movement of magma filling the cracks in Mid-Ocean Floor Ridges LITHOSPHERE - 100 km thick - “floats” because it’s less dense than other materials - rigid and brittle - fractures to produce earthquakes - interior of lithospheric plates are tectonically stable ASTHENOSPHERE - 100-660 km thick  - viscoelastic and NOT liquid - weak and deformable layer below the lithosphere (plastic) CONVECTION CURRENT - hot, plastic-like material rises from the mantle, moves horizontally, cools, and sinks back down to the mantle - provides enough energy to move plates around JOHN TUZO WILSON - geophysicist who pieced Wegener & other scientists’ ideas to form plate tectonics - combined continental drifting with large plate movement/pressures PLATE BOUNDARIES - fracture that separates one plate from another CONVERGENT - plates move closer together CONTINENTAL-CONTINENTAL - formation of mountains (Himalayas, European Alps, Everest, etc.) OCEAN-CONTINENTAL - ocean plate subducts because of its density - volcanoes (Pacific Ring of Fire & Andes Mountain) & trenches are formed - may cause earthquakes OCEAN-OCEAN - ONLY one ocean plate subducts - forms trenches (Mariana Trench at 11km deep) & volcanic arcs - can form earthquakes that may cause tsunamis DIVERGENT - caused by plates moving apart where new crust is created by magma rising to the surface OCEAN-OCEAN - may form Mid-Ocean Ridges (longest recorded is the Mid-Atlantic Range) - magma from the mantle moves up and solidifies to form new oceanic crust - volcanic activity (fissure volcanoes), shallow earthquakes CONTINENT-CONTINENT - form Rift Valleys that may develop into a linear sea (ex. The Red Sea) - Iceland is a country with a divergent boundary at its middle - shallow earthquakes & numerous normal faults TRANSFORM - plates slide past each other - formation of faults FAULT - fracture/fissure where ground movement has occurred or may occur again FAULTING - cause of Tectonic Earthquakes TYPES