Various-Potential-Earthquake-Hazards.pdf

VARIOUS POTENTIAL EARTHQUAKE HAZARDS Learning Competency Identify various potential earthquake hazards. DRR11/12-If-g- 17 Learning Competency Recognize the natural signs of an impending tsunami DRR11/12-If-g- 18 EARTHQUAKE HAZARDS Earthquake hazards include any physical phenomenon associated...

VARIOUS POTENTIAL EARTHQUAKE HAZARDS Learning Competency Identify various potential earthquake hazards. DRR11/12-If-g- 17 Learning Competency Recognize the natural signs of an impending tsunami DRR11/12-If-g- 18 EARTHQUAKE HAZARDS Earthquake hazards include any physical phenomenon associated with an earthquake that may affect human activities. There are several hazards that could happen during or after an earthquake. These hazards are generally classified into two; the primary hazards and secondary hazards. Primary hazards are those that have a direct result during an earthquake, these are: 1.Ground shaking 2.Ground or surface rupture 3.Liquefaction 4.Earthquake-induced landslides GROUND SHAKING This describes the vibration of the ground where an earthquake occurs which is usually recorded in terms of intensity. GROUND SHAKING Ground shaking can be a hazard or a trigger for other hazards such as landslides or tsunamis. GROUND SHAKING There are several factors that can affect the intensity of ground shaking during an earthquake, such as: 1.) magnitude of the earthquake; 2.) distance from the epicenter; and 3.) local geological conditions. mag nit ude The spot where an earthquake began is termed as the focus. From the focus, the energy created moves outward in all directions in a form of seismic waves. The epicenterof an earthquake is the point on the Earth’s surface located directly above the focus.  The 2004 Indian Ocean tsunami caused one of the largestnatural disastersin recorded history, killing at least 225,000 people across a dozen countries, withIndonesia,Sri Lanka,India,Maldives, andThailandsustainingmassive damage. GROUND SHAKING Most damages during an earthquake are result of the ground shaking which passes beneath the roads, buildings and other infrastructure. Many buildings and other structures in Pampanga have been damaged due to ground shaking caused by a magnitude-6.1 earthquake which occurred in April 22, 2019. https://www.sunstar.com.ph/article/1802326/manila/local-news/5-dead-in-pampanga-after-strong-quake GROUND RUPTURE Ground rupture happens on areas where the fault zone moves. Structures built adjacent to the fault will survive but those built across these zones will collapse. Any structures built across the fault is at risk of being torn apart as the two sides of the fault slip past each other. Surface rupture is not a single line with a fixed width but a zone with variable width where fractures have developed which are called as deformation zones. https://www.conservation.ca.gov/cgs/alquist-priolo https://r3.rappler.com/move- ph/issues/disasters/175082-phivolcs-ground-rupture- earthquake-leyte https://r3.rappler.com/move- ph/issues/disasters/175082-phivolcs-ground-rupture earthquake-leyte https://phys.org/news/2013-10-philippine- earthquake-miles-long-rocky-wall.html GROUND RUPTURE To avoid risks that can be caused by surface rupture, we should avoid building structures above or near the fault lines. PHIVOLCS recommends a five-meter buffer zone from the edge of the deformation zone for building structures One of the best examples of surface rupture happened during the 1999 Chi- Chi Earthquake in Taiwan under the Bei- Fung Bridge. The rupture lifted the uppe stream to a height of about 5 to 6 meter which results to a new waterfall. h t t ps://www.research gat e.n et /figure/6-m et ers-of-rev erse-faul t -surface-rupt from -the-1999-Chi-Chi-Taiwan-Earthquake-The_fig1_304218383 The 2013 Bohol Earthquake also lifted a mass of land about two kilometers long and two meters high. Geologists from PHIVOLCS found a surface rupture which is part of the reverse fault called the North Bohol Fault about 6 km long. https://www.phivolcs.dost.gov.ph/index.php/earthquake/earthquake-hazards EARTHQUAKE-INDUCED LANDSLIDES Landslides refer to a wide range ground movement such as rock fall and debris flow. Strong earthquake and ground shaking greatly increase the possibility of landslides in areas susceptible to ground failure. EARTHQUAKE-INDUCED LANDSLIDES Typically, a magnitude-4.0 earthquake is strong enough to trigger rock fall. Although, gravity acting on a steep slope is the primary reason for all landslides, there are other contributing factors. EARTHQUAKE-INDUCED LANDSLIDES The other contributing factors are: Over steepened slopes created by erosion in rivers, glaciers or ocean waves EARTHQUAKE-INDUCED LANDSLIDES The other contributing factors are: Rock and soil slopes weakened through saturations by heavy rains Excess weight from accumulation of rain EARTHQUAKE-INDUCED LANDSLIDES The other contributing factors are: Weak slopes due to the stockpiling of rock or ore from waste piles or from humanmade structures. LIQUEFACTION This occurs when sand or soil and groundwater mixed during an earthquake with a magnitude of 4.5 and higher which makes the ground very soft and exhibits properties similar to that of a quicksand. LIQUEFACTION When liquefaction occurs under a building, the building may start to lean, tip over or sink for several meters. The ground will eventually be settled again after the shaking stopped and the water has gone back into the ground. Areas that have groundwater close to the surface and have soil which is sandy is more prone to liquefaction. LIQUEFACTION Liquefaction has been identified as responsible for tremendous amounts of damages in historical earthquakes around the world. Areas such as floodplains, sand bars, coastal areas, swamps, marshes, river deltas and reclaimed areas are highly susceptible to liquefaction. A perfect example of liquefaction is during the 1990 Luzon Earthquake in Dagupan. Secondary earthquake hazards are results of the primary hazards, which are to be more disastrous. Secondary hazards include the following: 1.Tsunami 2.Seiche 3.Flooding 4.Fire TSUNAMIS Tsunamis are huge waves caused by an earthquake that originate beneath the ocean and can cause great destruction when it reaches the land. There are two types of tsunamis; a. locally-generated tsunamis, which are caused by earthquakes from nearby trenches and b. far-field tsunamis, which are generated by earthquakes from sources that are located farther from the area of impact 1976 Moro Gulf Earthquake and the 1994 Mindoro Earthquake are some of the recorded locally-generated tsunamis. The danger of the locally-generated tsunamis are the lesser amount of time before the waves arrive, usually 10 minutes after the huge shaking. Far-field tsunamis on the other hand usually takes hours before the waves arrive, depending on how the source was. 1994 Mindoro Earthquake Magnitude 7.1 At least 78 people killed and 225 injured on Luzon and Mindoro. A local tsunami contributed to extensive damage (VII RF) in the Calapanand Puerto Galera areas. More than 797 houses destroyed and 3,288 damaged on Mindoro. Seven houses destroyed at Batangas, Luzon. Liquefaction, sand boils and surface faulting occurred in the epicentral area. Felt (IV RF) at Batangas, Guinayangan, Manila and Tagaytay City; (III RF) at Quezon City, Luzon. Also felt (II RF) on Masbate. NATURAL SIGNS OF AN IMPENDING TSUNAMI  NATURAL SIGNS OF AN IMPENDING TSUNAMI 1.Feel an earthquake If the ground shakes under your feet in a coastal region, a tsunami may have been caused by strong undersea earthquake. However, you may not feel an earthquake if the event is far away.  NATURAL SIGNS OF AN IMPENDING TSUNAMI 2. See ocean water disappear from the beach, bay, or river Before a tsunami arrives, water may recede from the shoreline before returning as a fast-moving wall of water. If you notice the water is declining, tell your family and friends and  NATURAL SIGNS OF AN IMPENDING TSUNAMI 3. Rumbling Sound of Approaching Waves If you hear a loud roar approaching (a bit like a passenger jet or a train). tell as many people as possible. It could be a tsunami approaching.  Tsunami Prone Areas in the Philippines https://www.phivol cs.dost.gov.ph/ind ex.php/news/9291- press-release-are-  PHIVOLCS Tsunami Warning Signs AdvisoryA large earthquake is No - generated but either: evacuation GREEN 1.There is no tsunami needed. The No generated by this advisory is Tsuna event or issued for mi 2.A tsunami was information Threat generated but will purposes only. not reach the Philippines  PHIVOLCS Tsunami Warning Signs Advisory PHIVOLCS will monitor No – sea level changes evacuation YELLOW Sea and provide updates order is in Level effect. Public Change is advised to Monitori wait and listen ng for updates.  PHIVOLCS Tsunami Warning Signs Advisory Minor sea level People are advised to stay away from the beach and not to go to – disturbance is the coast. People whose houses ORANGE expected in are located very near the Minor shoreline are advised to move some coastal farther inland. Owners of boats in Sea Level areas with wave harbors, estuaries, or shallow coastal water of the affected Disturba heights of less provinces should secure their than one (1) boats and move away from the waterfront. Boats already at sea nce meter above the are advised to stay offshore in expected ocean deep waters until further notified. tides.  PHIVOLCS Tsunami Warning Signs Advisory Destructive tsunamis Immediate evacuation of – are generated with social communities that TSUNAMI life threatening wave maybe affected are strongly WARNING heights. (A advised. Owners of boats in harbors, estuaries, or shallow destructive tsunami is coastal water of the affected expected to arrive to provinces should secure their Philippines coastlines boats and move away from with wave heights of the waterfront. Boats already greater than one (1) at sea are advised to stay meter above the offshore in deep waters until expected ocean further notified. tides.) SEICHE Seiche is standing waves that are created in a closed or partially-closed body of water such as lakes, reservoir, swimming pools and bays due to strong wind or earthquake. Seiche has also a to- and-fro motion that is produced by a forcing motion on an enclosed body of water. The standing wave is a superposition of waves that travels the whole length of the water and then reflected back to the opposite position. FLOODING When tsunami hits the land, the water that remains can flood the coastal areas. When an earthquake breaks a dam, the water that flows out can cause severe flooding on low-lying areas. FIRE After an earthquake, there is a possibility that a fire will break out. Fires can be a result of a candle or lantern that are tipped off during the earthquake or can also be because of gas lines that leaked and sparks from broken electric and utility wires. To worsen the scenario, earthquake can also block the water source or block the way of the firefighting equipment and vehicles.