AUSTAWIE RA ONA PLATE ANTARCTIC RAM http://pubs.usgs.gov Figure 2. Map of Plate boundaries As shown in Figure 2, there are seven relatively large plates and a number of smaller ones, including the Philippine plate. The plates move very slowly but constantly, and this movement is called tectonics; thus the theory of moving lithospheric plates is called plate tectonics. Before we study more about plate tectonics, let's discuss first one of the consequences of moving crustal plates which is crucial in studying plate tectonics: earthquake. You have learned in your Grade 8 Science that an earthquake releases three types of seismic waves; Primary (P-waves), Secondary (S-waves), and Long surface waves (L-waves). The first two travel into the Earth's interior while the last one on the surface. These waves travel at different velocities; thus, do not arrive at a seismic recording station at the same time. The farther the recording instrument is from the focus, the greater the differer times of the first P-wave compared to the first S-wave. The dif arrival time will tell us the distance of the earthquake's focus fro 12 / 84 recording station. However, it does not tell in which direction it can 7 rights reserved. No part of this material may be reproduced or transmitted in any form or by any means electronic or mechanical including photocopying-without written permission from the DepEd Central Office. First Edition, 2015. If we have at least three recording stations that can tell how far away from them the earthquake occurred, the epicenter can determined using the triangulation method. It uses distance information from three seismic stations to locate the earthquake epicenter. On a map, circles are drawn around each seismic station. The radii of the circles are scaled to the estimated distance from the station to the earthquake. The three circles will intersect at one point that locates the earthquake. The next activity will give you a first-hand experience on how to locate earthquake epicenter ...
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