Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Magnitudes of Earthquakes • There are two main methods of measuring the strength of an earthquake. • Mercalli Scale: This scale is based on what people felt, what objects moved, and how much damage was done by the Earthquake. • Richter Scale: This scale is based on the equivalent kg of explosives needed to create the same effect. – This scale goes up by an order of ~10 every time. • 1=56kg, 2=560kg, 3=5600kg, • 9=56000kg, 10=560,000kg Earthquake Waves • By determining the time of arrival for both the P and S waves at a location we can determine how far away the Earthquakes epicenter from the seismograph. • This does not tell us what direction the waves are coming from though. Locating the Epicenter of an Earthquake Part I: Finding the distance to the epicenter. • Step 1: – Determine the difference in arrival time for your P-wave, and your S-wave. Locating the Epicenter of an Earthquake Part I: Finding the distance to the epicenter. Step 2: – Take out your ESRT. Open to the Travel Time Graph on page 11. • Step 3: – Use the vertical scale (time) to mark off the difference in arrival time on a scrap sheet of paper. Locating the Epicenter of an Earthquake Part I: Finding the distance to the epicenter. • Step 4: – Make sure to keep your scrap paper vertical! Slide it along the curves until you find the place where your marks each line up on one of the curves. Locating the Epicenter of an Earthquake Part I: Finding the distance to the epicenter. • Step 5: – Read off the distance from the horizontal axis that corresponds to this spot. This is the distance between the epicenter and your seismograph location. Locating the Epicenter of an Earthquake Part I: Finding the distance to the epicenter. • Step 6: – Repeat steps 1-5 for at least 2 other locations. – It is necessary to have at least 3 stations, if you do not you can not be sure of the exact location of the epicenter. Locating the Epicenter of an Earthquake Part II Locating the Epicenter • Step 1: – Find the location of your first seismographic station on the map. • Step 2: – Use a compass or string to create a circle with its center at your seismograph location, and a radius equal to the distance you found. Locating the Epicenter of an Earthquake Part II: Locating the Epicenter • Repeat this procedure around two other seismographic stations. • Where the three circles all intersect (cross) is where your epicenter is located. • If the circles do not all intersect, but form a small triangle, the epicenter is the center of the triangle. Locating the Epicenter Locating the Epicenter of an Earthquake Part III: Origin time of the Earthquake • From the distances determined in Part I, determine how long it would take a P wave to travel that distance. Origin Time of Earthquake • Step 1: • Find the distance on the horizontal axis. • Go up to the point where you hit the P-wave travel line. • Go over to the vertical axis and read off the time. Origin Time of Earthquake • Step 2: – Taking the time found in step 1, subtract this from the arrival of the P wave and that is the original time of the earthquake. – (3:21pm)-(7 min 40 seconds) Uses of Earthquake Waves • We now know…(or should know) that Pwaves travel faster then S-waves. • We also know that P-waves travel through solids and liquids, and S-waves travel only through solids. • Scientist have found that as energy in waves passes through material it can bend, depending on the density of the material. Bending Waves: • Have you ever looked into a fish tank and seen two images of the same thing? • This is an example of waves of light being bent. • When P-waves change from traveling through a liquid to a solid they also bend. • This bending forces them to change direction slightly. The Effects of Bent waves. What this means to seismograph Stations • Since S-waves can not travel through liquids, they STOP when they hit a liquid layer. • Since P-waves slow down when they enter a liquid, they bend. • This creates a “Shadow Zone”, an area where no waves from an earthquake are picked up by a seismograph. Wave Behavior • These shadow zones occur at a distance of 105-140 degrees (360 degrees in a circle) from the Epicenter of the quake. • Between 140 degrees in each direction only Pwaves were seen. • These wave behaviors let scientist know what phase of matter the material in the earth, as well as its composition. Into the Earth • This is what allows scientist to infer what the interior of the Earth is like. • Although the Earth appears to be made up of solid rock, it’s actually made up of three distinct layers • The three main layers are the crust, the mantle and the core. Crust • The crust is the thin, solid, outermost layer of the Earth. • The crust is thinnest beneath the oceans, averaging only 5 kms thick. • It is thickest beneath large mountain ranges. • Continental crust varies in thickness, but averages about 30-35 km. • Beneath large mountain ranges, (Himalayas or the Sierra Nevada), the crust reaches a thickness of up to 100 km. (upper) Mantle • The layer below the crust is the mantle • The mantle has more iron and magnesium than the crust, making it more dense • The uppermost part of the mantle is solid and, along with the crust, forms the lithosphere • The rocky lithosphere is brittle and can fracture. This is the zone where earthquakes occur. • It’s the lithosphere that breaks into the thick, moving slabs of rock that geologist’s call tectonic plates. Mantle (lower) • As we descend into the Earth temperature rises and we reach part of the mantle that is partially molten, the asthenosphere. • As rock heats up, it becomes pliable or ‘plastic’. Rock here is hot enough to fold, stretch, compress, and flow very slowly without fracturing. (Silly Putty®) • The plates, made up of the relatively light, rigid rock of the lithosphere actually ‘float’ on the more dense, flowing asthenosphere! Core • At the center of the Earth lies the super-dense core. • It has a diameter of 3486 kms. • The core is larger than the planet Mars! • The core of the Earth is made up of two distinct layers: – A liquid outer layer and a solid inner core. Unlike the Earth’s outer layers with rocky compositions, the core is made up of metallic ironnickel alloy. – It’s hard to imagine, but the core is about 5 times as dense as the rock we walk on at the surface! Trends in the Earths Interior • As you progress further and further into the Earth the more dense the material becomes. • This is do in part to: – the weight of material overhead. – Getting closer to the Earths Core Trends in the Earths Interior • As you progress further and further into the Earth the hotter the material becomes. • This is do impart to: – Boyles Law: Compression causes heating. – Heat lost by the Earth’s core – Radio-active decay giving off heat.