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Cecelia Villa

Physical Geology
Fall 2008

Beautiful GUAM, USA and the Adventurous Earthquakes

           We flew into Guam at 10:30 pm on December 20, 1999. The island looked small and nicely lit compared to the black ocean we had just flown over for 8 hrs from Hawaii. It was nice to see land and as the plane descended it felt like we were back to being human instead of birds. Driving to our hotel in Agat, the southern part of the island seemed like a new world. Looking to the right side of the road continued to be scary as the black ocean kept creeping at us. Driving through the main road of the island seemed as if we were being taken through the scenic route. The road was somewhat narrow compared to the ones I had always known about in the city but to have the jungle and life to the left side of our vehicle and the ocean to the right, seemed as if the adventure was not ending. To our surprise in the morning, that road was going to be the main road that travels throughout the island, one we would drive to and from daily for two years.Map of Guam

           The morning after, we got to see the beautiful beach we had right outside our rooms. As we reflected of our new life on the other side of the world sitting on a couch we heard a parrot make sounds that we were unfamiliar with. We said it was nice to hear those island sounds as our couch began to shake. It happened too quick enough for us newcomers to grasp what had happened. We all thought my husband had set up the couch to move scaring us. He laughed as he denied any involvement. He had heard from new co-workers about those little tremors, but yet, the kids and I had no clue. He himself didnít expect to experience one after getting to the beautiful, paradise like island of Guam. Once meeting his new co-workers, the question of, ďDid you feel the earthquake?Ē was one question we would hear of repeatedly. It must have been a tremor but to those of us who are not accustomed to this, every time the earth makes any unfamiliar movement to where furniture rattles, we call it an earthquake. This happened more frequently than one would like but yet you cannot get used to them. We had heard of the Big One that had hit in August of 1993 but the reassurance of others that Guam is earthquake ready somewhat eased but not erased the scary feelings when experiencing a tremor, an earthquake. There was always talk about another big one to come but the kids and I somewhat got to like the feeling of experiencing earthquakes. It was another exciting thing to brag about when we talked to our family back home in El Paso, TX where they donít experience these earthly movements.

                                              Gab Gab Beach, Naval Station, Guam               

          All seemed well and fun living in this paradise island as we welcomed a new family one October day. On October 12, 2001,a new family was assigned from a fort in Texas. The husband, a fellow soldier friend of my husband had just arrived with his wife and four kids. I had made dinner for his wife and kids as my husband took a drive with his new co-worker around the island. The kids were playing upstairs as his wife and I watched a movie. I was warning her about the tremors that seemed to happen quite often. We heard a roar outside and she asked what that was. I had experienced small tremors that had been silent, this was a noise I was unfamiliar with.  I suddenly was too scared myself in realizing what was about to happen as local friends had talked about with bigger so called tremors. Suddenly, the floor felt soft, creaks began to be heard from upstairs. The walls began to move as the mirrors I had began moving too. The house felt like if it was boat. The swaying motion got my new scared friend up on her feet as I got up myself. The kids upstairs began to scream, she and I started running upstairs when the motion shifted to the opposite way, we were both screaming along with the kids. As we made our way up the stairs, the whole house shook, but not in a swaying motion but as if someone just shook it. Suddenly the lights went out, we felt another swaying motion and it was over. Being in an island in the middle of the Pacific Ocean can get pretty dark and scary. As we made sure everyone was ok, we walked outside to an open space as the MPís came to see if anyone needed help. Thank God we and our neighbors were ok. I knew then what my local friends would say that Guam was earthquake proof. We all agreed that was no tremor but a good size earthquake. The next morning, we found out preliminary data indicated a very strong earthquake registering Ms 7.0 (NEIC), Mw 7.0 (HRV), Mw 6.9 (HRV) occurred at 15:02:20, October 12, GMT in the Western Pacific Ocean. As strong as it was and felt, it caused significant non-structural damage to the island. There was no word of injuries or deaths.

         According to Paul Hattori, a local seismologist, Guam actually has several earthquakes per day, but most of them are too small to be detected by humans. Every few weeks we get one that is big enough and close enough for people to notice.

         People love to argue about which is worse, typhoons or earthquakes. Some people say that typhoons are worse because they last longer and there are more of them. But most people think that earthquakes are worse because they hit without warning. At least with typhoons, you know they are coming.

         One of the coolest things about earthquakes is how different they are from each other. Some are noisy and some are quiet. Sometimes you can hear them coming, sounding like a distant freight train, or a great stone door sliding shut. Once they are on you, of course, you can hear the stuff in your house rattling. Some of them last a long time and you can feel them vibrating for ages, it seems. Others feel like a single, simple lurch. You feel the displacement of the Earth's surface; you feel your latitude and longitude changing slightly. Others produce a rolling sensation, as if you were on a raft out on the open sea. If you are outside during one of these, you can actually see the ground rolling. Some, like the Big One in August 1993, are a combination of all these. Paul Hattori is pretty sure that our big earthquake was actually two earthquakes with different foci, occurring about 7 seconds apart and on different sides of the island. The epicenter(s) couldn't be located precisely, partly because Paul's equipment was knocked out by the earthquake, but he's pretty sure that the epicenter(s) were not directly underneath us. The focus was fairly deep. If it had been shallow, and if it had been right under us, it would have been a lot worse.

          The latest earthquake recorded in Guam, USA was 4.9 in magnitude. This happened Friday, November 28, 2008 at 07:53:07 PM local time at epicenter. Preliminary Earthquake Report: The location was 12.79N 143.43E, the depth was 111.6 kilometers Distances 160 km (100 miles) WSW of Hagatna, Guam

          According to the USGS, Guam is the largest and southernmost island of the Mariana Islands. It rises steeply from the ocean floor, a short distance to the north of the world's greatest known oceanic depth. Felt earthquakes are frequently reported. 


        I learned that one of the reasons Guam experiences frequent earthquakes was because we were so close to the Mariana Trench. The Mariana Trench is the deepest point in Earth's oceans and it just happens to be close to Guam. The bottom there is 10,924 meters (35,840 feet) below sea level. If Mount Everest, the highest mountain on Earth, were placed at this location it would be covered by over one mile of water.

                                            Earthquake Location    
Map of the Mariana Trench - Deepest Point in Earth's Oceans - Image by CIA


       According to the ocean is deep here because The Mariana Trench is located at a convergent plate boundary. Here two converging lithospheric plates collide with one another. At this collision point, one of the plates descends into the mantle. At the line of contact between the two plates the downward flexure forms a trough known as an ocean trench. An example of an ocean trench is shown in the diagram below.





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