LITHOSPHERIC PLATES LITHOSPHERE ▪ Made up of the crust and uppermost mantle. ▪ Earth is generally composed of 58 lithospheric plates. ▪ They are constantly in motion relative to one another ▪ It is said to be in constant but slow motion. LITHOSPHERE ▪ The Arctic Ridge has the slowest rate with less than 2.5 centimeter per year. ▪ The East Pacific Rise near Easter Island has the fastest rate with more than 15 cm per year. Can you name these LITHOSPHERIC PLATES? Eastern Aleutian Arc Figure 1 . Map of Lithospheric Plates http://pubs.usgs.gov • Pacific Plate • Eurasian Plate • African Plate • North American Plate • South American Plate • Antarctic Plate • Indo-Australian Plate What are the major plates? -SIAN PLATE INDO-AUSTRALIAN PLATE NORTH AMERICAN PLATE PACIFIC PLATE EURA- SOUTH AMERICAN PLATE AFRICAN PLATE ANTARCTIC PLATE Figure 2 . 7 Major Tectonic Plates http://pubs.usgs.gov • Arabian Plate Plate • Juan de Fuca Plate • Caribbean Plate • Philippine Sea Plate • Cocos Plate • Scotia Plate • Indian Plate ❖ Nazca Plate What are the other plates? Juan de Fuca Plate Philippine Sea Plate Caribbean Plate Cocos Plate Arabian Plate Indian Plate Nazca Plate Scotia Plate Figure 3. Other Plates http://pubs.usgs.gov In which directions do they move? de Figure 4 . Direction of plates movement ▪ Nazca and South American ▪ Antarctic and South American ▪ Eurasian and Philippine Plate Which plates move TOWARD each other? ▪ North American and Eurasian ▪ South American and African ▪ Pacific and Antarctic ▪ Antarctic and Australian Which plates move AWAY each other? Which plates move SIDE-bySIDE each other? ▪ Part of North American Plate and Eurasian Plate How can you relate the occurrence of earthquake with the movement of these lithospheric plate? EARTHQUAKE • It is the sudden shaking of the ground caused by the pressure between two moving tectonic plates. • When plates move suddenly, they release an incredible amount of energy that is changed into wave movement. • About 90% of earthquakes are produced along faults, tectonic plate boundary zones, or along the midoceanic ridges. Where on Earth do earthquakes usually occur? Figure 5 . Locations of Earthquake Epicenters https://www.pmfias.com/earthquakes-shallow-focus-deep-focus-earthquakes/ How are earthquakes distributed on the map? EARTHQUAKE • About 90% of earthquakes are produced along faults, tectonic plate boundary zones, or along the mid-oceanic ridges. • More than 150,000 quakes strong enough to be felt are recorded each year. Are there areas with no earthquakes recorded? Figure 5 . Locations of Earthquake Epicenters EARTHQUAKE • Large part of the Pacific ocean, northernmost Asia, majority of Europe, eastern portion of North and South America and western Africa. Why is it important for us to identify areas which are prone to earthquakes? Central Luzon, Eastern Visayas and Southern Mindanao are at high to moderate risk of earthquakes while Northern Luzon, Southern Luzon, Central Visayas, and Central Mindanao are of low risk. https://www.dost.gov.ph How to locate earthquake epicenter? EARTHQUAKE WAVES SEISMOGRAPH is the instrument that record earthquake waves. SEISMOGRAMS are traces of amplified, electronically recorded ground motion made by seismographs. LOCATING THE EPICENTER A. Compute mathematically using the formula: B. Triangulation Method 1. Using the seismogram, compute for the lag time. A. Compute mathematically the distance of an epicenter. LAG TIME - interval between the arrival time of P and S waves. Lag time = S-wave arrival time – P-wave arrival time = 21 seconds – 11 seconds Lag time = 10 seconds 2. Identify the distance of the epicenter to the seismic station using the formula: A. Compute mathematically the distance of an epicenter. Where: d = distance (km) Td = time difference in the arrival time of P and S-wave or the Lag Time *8 seconds is the interval between the time of arrival of the P-wave and S-wave at a distance of 100 km d = 10 seconds/8 seconds = 1.25 x 100 km d = 125 km The epicenter of the earthquake is 125 km from the seismic station • It needs at least three recording stations that can tell how far away from them the earthquake occurred. B. Using Triangulation Method. • It uses distance information from three seismic stations to locate the earthquake epicenter. Recording Station Time difference Distance of of the S- wave Distance in cm epicenter to the and P-wave 1cm = 1000 km station (km) (seconds) Sitka, Alaska 200 seconds 2500 2.5 Charlotte, N.C. 280 seconds 3500 3.5 Honolulu, Hawaii 360 seconds 4500 4.5 B. Using Triangulation Method. Recording Station Time difference of the S- wave and P-wave (seconds) Distance of epicenter to the station (km) Distance in cm 1cm = 1000 km Sitka, Alaska 200 seconds 2500 2.5 Charlotte, N.C. 280 seconds 3500 3.5 Honolulu, Hawaii 360 seconds 4500 4.5 • On map, circles are drawn around each seismic station. The radii of the circles are scaled to the estimated distances from the station to the earthquake epicenter. The point of intersection is the location of the epicenter. https://www.medford.k12.nj.us/cms/lib/NJ01001377/Centricity/Domain/ 88/Earthquake%20Epicenter%20Lesson% 203%20with%20header.pdf USE OF TIME-TRAVEL GRAPH https://www.youtube.com/watch?v=lC--uXieK9s
