Earth science unit 1

What is a fault?

• A fault is a fracture or zone of fractures between two blocks of rock. Faults allow the blocks to move relative to each other. This movement may occur rapidly, in the form of an earthquake - or may occur slowly, in the form of creep.

What is an epicenter?

• the point on the earth's surface vertically above the focus of an earthquake.The epicenter is typically where the strongest shaking is felt and is used to determine the location of the earthquake's origin.

Where do earthquakes usually occur?

• Earthquakes usually occur at plate boundaries where different plates meet and interact, often leading to tectonic activity such as subduction, collision, or sliding past one another. These interactions can create stress that eventually results in an earthquake, making these regions more prone to seismic events.

What kind of energy is released when an earthquake occurs?

• Seismic Energy is released. This energy travels through the Earth's crust in the form of seismic waves, which can be detected by seismographs and can cause significant ground shaking and damage.

Name the fault that runs through San Francisco.  What type of fault is it?

• The fault that runs through San Francisco is the San Andreas Fault. It is classified as a transform fault, where two tectonic plates slide past one another horizontally, leading to significant seismic activity in the region.

Name the three seismic waves in order of fastest to slowest.

• The three seismic waves in order of fastest to slowest are:

  1. Primary waves (P-waves) - These are compressional waves that travel through solids, liquids, and gases.

  2. Secondary waves (S-waves) - These are shear waves that can only travel through solids.

  3. Surface waves - These waves travel along the Earth's surface and are typically the slowest, causing the most damage during an earthquake.

Describe the three seismic waves.

• Primary waves (P-waves): These are compressional waves that travel through solids, liquids, and gases, making them the fastest seismic waves and the first to be detected by seismographs.

• Secondary waves (S-waves): These are shear waves that can only travel through solids, arriving after P-waves and causing significant shaking as they move perpendicular to the wave direction.

• Surface waves: These waves travel along the Earth's surface and are typically the slowest, causing the most damage during an earthquake due to their larger amplitude and longer duration.

How do seismologists determine the epicenter of an earthquake? How many seismograph stations are required?

• To determine the epicenter of an earthquake, seismologists analyze the arrival times of P-waves and S-waves at multiple seismograph stations. Typically, at least three seismograph stations are required to accurately triangulate the epicenter by measuring the time difference between the arrival of these waves. This method allows seismologists to create a triangulation point where the circles drawn from each station intersect, pinpointing the earthquake's location.

What is a seismograph?

• A seismograph is an instrument that detects and records the vibrations caused by seismic waves as they travel through the Earth. It consists of a mass suspended on a spring, which remains stationary while the ground moves during an earthquake, allowing the relative motion to be recorded on a rotating drum or digital storage.

How do we determine an earthquake's magnitude?

• Magnitude is determined using data from seismographs, specifically by measuring the amplitude of the seismic waves recorded. The most common scales used for this purpose are the Richter scale and the moment magnitude scale (Mw). The Richter scale calculates the magnitude based on the amplitude of the largest wave recorded, while the moment magnitude scale takes into account the seismic moment of the earthquake, which includes the area of the fault that slipped, the amount of slip, and the rigidity of the rocks involved.

What are the layers of the earth starting with the surface?

• Crust: The outermost layer, composed of solid rock and minerals, which includes the continents and ocean floors.

• Mantle: Located beneath the crust, this layer is made up of semi-solid rock that flows slowly, allowing tectonic plates to move.

• Outer Core: A liquid layer composed mainly of iron and nickel, which generates the Earth's magnetic field through its movement.

• Inner Core: The innermost layer, consisting of solid iron and nickel, with temperatures reaching up to 5,700 degrees Celsius.

Describe the lithosphere and the asthenosphere.

• Lithosphere: The rigid outer layer of the Earth, consisting of the crust and the uppermost part of the mantle, which is divided into tectonic plates that float on the more fluid layers beneath.

  Asthenosphere: A semi-fluid layer located below the lithosphere, within the upper mantle, that allows for the movement of tectonic plates due to its ability to flow slowly over geological time.

What kind of plate boundary occurs where two plates grind past each other?

• A transform boundary

What is a divergent plate boundary?

• Two tectonic plates moving away from each other

What can result from a divergent boundary and a convergent boundary?

• Convergent: Earthquakes and volcanoes

• Divergent:massive fault zones in the oceanic ridge system. Spreading is generally not uniform, so where spreading rates of adjacent ridge blocks are different, massive transform faults occur. These are the fracture zones, many bearing names, that are a major source of submarine earthquakes.

What is the East African Rift Valley?

• The East African Rift Zone includes a number of active and dormant volcanoes. The East African Rift Valley (EAR) is a developing divergent plate boundary in East Africa. Here the eastern portion of Africa, the Somalian plate, is pulling away from the rest of the continent, that comprises the Nubian plate.

What is the Ring of Fire?

• a string of volcanoes and sites of seismic activity, or earthquakes, around the edges of the Pacific Ocean. Roughly 90 percent of all earthquakes occur along the Ring of Fire

What is subduction?

• the sideways and downward movement of the edge of a plate of the earth's crust into the mantle beneath another plate.

What is a volcanic island arc?

• Volcanic island arcs are major structures of ocean basin features. They are long, typically curved, volcanic island chains found on the basin margins. Their shape is an important feature. They are typically concave toward the bordering continent and convex toward the ocean basin. A deep trench is located on the ocean basin side of the arc. They form when two plates subduct,

What is plate tectonics?

• Plate tectonics is a scientific theory that explains how major landforms are created as a result of Earth’s subterranean movements. The theory, which solidified in the 1960s, transformed the earth sciences by explaining many phenomena, including mountain building events, volcanoes, and earthquakes.

What kinds of dangers are associated with earthquakes?

What are the three types of rocks?

• Sedimentary, metamorphic, igneous

Explain how sedimentary rocks form.

• from deposits of pre-existing rocks or pieces of once-living organism that accumulate on the Earth's surface. If sediment is buried deeply, it becomes compacted and cemented, forming sedimentary rock.

Explain how metamorphic rocks form.

• when rocks are subjected to high heat, high pressure, hot mineral-rich fluids or, more commonly, some combination of these factors. Conditions like these are found deep within the Earth or where tectonic plates meet.

Explain how igneous rocks form.

• when hot, molten rock crystallizes and solidifies. The melt originates deep within the Earth near active plate boundaries or hot spots, then rises toward the surface.

Draw the rock cycle using the following words: igneous rock, sedimentary rock, metamorphic rock, melting, magma, cooling, metamorphism (heat, pressure, stress), weathering, sediments, deposition