Earthquake Reviewer PDF

EARTHQUAKE An earthquake is a feeble shaking to violent trembling of the ground produced by the sudden change / displacement of rocks or rock materials below the earth’s surface. Sudden displacements along faults fissures in the solid and rigid layer of the earth generate Tectonic Earthquake...

EARTHQUAKE An earthquake is a feeble shaking to violent trembling of the ground produced by the sudden change / displacement of rocks or rock materials below the earth’s surface. Sudden displacements along faults fissures in the solid and rigid layer of the earth generate Tectonic Earthquakes. Those induced by the rising lava or magma beneath active volcanoes generate Volcanic Earthquakes. Classification of earthquake acc. To source mechanism: 1. Tectonic – due to movement of plates of the earth’s surface. 2. Volcanic – associated with volcanic activities w/c are triggered by fracturing of rocks. These occur beneath the edifice of active volcanoes and therefore, at very shallow depths. 3. Explosion – caused by underground detonation of chemical or nuclear devices. 4. Collapse – Occurs in regions of underground caverns and mines due to sudden collapse of the roof of the mine or cavern. 5. Earthquake due to massive landsliding Classification of earthquake according to the depth of focus: 1. Shallow focus – focus depth less than 70 kilometer. This is the most destructive type because it accounts 75% of energy is released during earthquake. 2. Intermediate focus – focus from 70 to 300 kilometer depth. 3. Deep focus – focus depth greater than 300 kilometer. Note: a. Focus is a point from which the seismic wave first emanates. b. Epicenter is a point on the ground directly above the focus. Dynamic Earth Structure: The Earth may be considered to have three concentric layers: Mantle, Outer Core (liquid) and Inner Core (solid). The sudden variation in the seismic wave velocity close to the crustal surface is due to Moho discontinuity (recognized by the Croatian seismologist Andrija Mohorovičić in 1909) and it is accepted as the boundary between the mantle and the crust. Continental Drift: By 135 million years ago, Laurasia had split into the continents of North America and Eurasia, and Gondwanaland had divided into the continents of India, South America, Africa, Antarctica and Australia.  Richard Field – one of the geologists who studied the geology of the ocean floor.  Harry Hess (1960) – proposed the theory of sea-floor spreading and suggested that the ocean floor is formed continuously by the magma that rises up from within the mantle into the central gorges of the oceanic ridges.  Alfred Wegener (1915) – German meteorologist who first documented The separation of African and South American continents. Subduction – geological process where two plates collide and one is pushed down below the other. The seismic activity is intense in subduction regions as in the case of mid-oceanic ridges due to high deformation rates between the colliding slabs. Theory of Global Plate Tectonics: Earthquake occurrence may be explained by the theory of large‐scale tectonic processes, referred to as ‘plate tectonics’. The theory of plate tectonics derives from the theory of continental drift and sea‐floor spreading. Plates are large and stable rigid rock slabs with a thickness of about 100 km forming the crust or lithosphere and part of the upper mantle of the Earth. The horizontal movement of the lithosphere is caused by convection currents in the mantle; the velocity of the movement is about 1–10 cm/year. Earthquake Prone Areas: 1. Along Tectonic Plate Margins According to the theory of continental drift, the lithosphere is divided into 15 rigid plates, including continental and oceanic crusts. The plate boundaries, where earthquakes frequently occur, are also called ‘seismic belts’. The Circum-Pacific and Eurasian (or Alpine) belts are the most seismically active.  The Circum-Pacific connects New Zealand, New Guinea, the Philippines, Japan, the Aleutians, the west coast of North America and the west coast of South America. The 1994 Northridge (California) and the 1995 Kobe (Japan) earthquakes occurred along the Circum‐Pacific belt.  The Eurasian belt links the northern part of the Mediterranean Sea, Central Asia, the southern part of the Himalayas and Indonesia. The Indian Ocean earthquake of 26 December 2004 and the Kashmir earthquake of 8 October 2005 were generated by the active Eurasian belt. There are three principal types of plate boundary along w/c relative movements of neighboring plates can occur and trigger the occurrence of earthquakes. They can be group as follows:  Divergent or rift zones: where new oceanic crust or lithosphere is created as the plates pull away from each other. An example of rift can be found in the middle of the Gulf of Corinth.  Convergent or subduction zones: where adjacent plates converge and collide. A subduction process carries the slab‐like plate, known as the ‘under‐thrusting plate’, into a dipping zone, also referred to as the ‘Wadati–Benioff zone’, as far downward as 650–700 km into the Earth’s interior. Two types of convergent zones exist: oceanic lithosphere boundaries (two plates of oceanic lithosphere collide) and continental lithosphere boundaries (two plates of continental lithosphere collide). Notes: If the leading edges of two plates pushing against each other are pre- existing ocean floors, the plates which is faster-moving sinks and descends into the earth’s interior (or subducts) beneath the slower-moving plate. If one plate contains continental landmasses near its leading edge (like the South American Plate) and the other contains only pre-existing ocean floor (like the Nazca Plate), the one with continents stays afloat and the other composed only of old ocean floors subducts. If both opposing plates contain continental masses (like the Indian and Eurasian Plates), neither of the two will subduct when the continents are finally brought together or collide along the leading edges. The trench that brought them together disappears and is replaced by mountain chains as they continue to interact by collision. The Himalayas, for example, came into being by the collision of the Indian Plate with the Eurasian Plate.  Transform zones or transcurrent horizontal slip: where two plates slide horizontally past each other but without creating new lithosphere or subducting old lithosphere. One example is San Andreas Fault in California. Intra-plate earthquakes generally fall into two groups: plate boundary-related and midplate. The former take place either in broad bands near plate edges and are tectonically linked to them or in diffuse plate boundaries. 2. Along Tectonic Plate Margins When two ground masses move with respect to one another, elastic strain energy due to tectonic processes is stored and then released through the rupture of the interface zone. The distorted blocks snap back towards equilibrium and an earthquake ground motion is produced. This process is referred to as ‘elastic rebound’. The resulting fracture in them Earth’s crust is termed a ‘fault’. Faults are breaks or zones of weakness in rocks along which displacements had occurred or can occur again. They may extend for hundreds of kilometers across the earth’s surface and tens of kilometers downward, even down to the base of lithosphere. Types of faults based on orientation of fault surfaces and nature of relative movement of displaced rock: 1. Dip-slip faults: one block moves vertically with respect to the other. If the block Underlying the fault plane or ‘foot wall’ moves up the dip and away from the block overhanging the fault plane or ‘hanging wall’, normal faults are obtained. Tensile forces cause the shearing failure of normal faults. In turn, when the hanging wall moves upward in relation to the foot wall the faults are reversed; compressive forces cause the failure. 2. Strike-slip faults: the adjacent blocks move horizontally past one another. Rate Of Motion Along Plate Margins And Faults: The rates of movement or velocities of relative motion between adjacent plates and fault blocks range from about one to twelve centimeter per year. Epicenter vs. Focus: Focus or hypocenter of an earthquake is the point under the surface where the rupture is said to have originated. Epicenter is a point on the earth’s surface situated nearest to where the earthquake exactly originates. The earthquake epicenter is obtained by projecting vertically to the earth’s surface the determined location of the focus in the earth’s interior.  The above discussion highlights one of the difficulties encountered in characterizing earthquake parameters, namely the definition of the source. It is clear that the source is not a single point, hence the ‘distance from the source’ required for engineering seismology applications, especially in attenuation relationships is ill-defined. Seismic Waves: A seismic wave is a mechanical wave of acoustic energy that travels through the Earth or another planetary body. It can result from an earthquake (or generally, a quake), volcanic eruption, magma movement, a large landslide, and a large man- made explosion that produces low-frequency acoustic energy. The energy radiates outward from the fault in all directions in the form of seismic waves like ripples on a pond. The seismic waves shake the earth as they move through it, and when the waves reach the earth's surface, they shake the ground and anything on it, like our houses and us! 4 types of seismic waves: 1. Body Waves – can be classified into two: Primary (P) waves and Secondary (S) waves. Both P-waves (primary) and S-waves (secondary) are body waves which are the fastest waves and can travel inside and surface of the Earth. P-waves are faster than S-waves, consequently,  the arrival times of P-waves are shorter than the arrival of S-waves and P- waves are the first waveforms observed in seismic recordings (seismograms).  different phases of S-waves are observed after P-waves on the seismograms. Primary waves (P-waves) are the fastest seismic waves (3.1 to 8.1 miles per second) and they travel parallel to the direction of seismic waves as compressional waves or pressure waves. S-waves are relatively slower than P-waves (1.9 to 3 miles per second) and they move perpendicular and side to side to the main direction of seismic waves.  2. Surface Waves Trapped body waves that propagate across Earth’s surface. The amplitudes of surface waves decrease with increasing depth and they do not travel towards the inner part of the crust. They are divided into two types and are called as: Love (LQ) waves and Rayleigh (LR) waves. In seismology, Love waves (also known as Q waves (Quer: German for lateral)) are surface seismic waves that cause horizontal shifting (perpendicular to the direction of wave propagation) of the Earth during an earthquake. Augustus Edward Hough Love predicted the existence of Love waves mathematically in 1911. They are formed when shear or S waves interact with the earth's surface or with shallow structures. Rayleigh waves – type of seismic surface wave that moves with a rolling motion that consists of a combination of particle motion perpendicular and parallel to the main direction of wave propagation. Rayleigh waves travel slower than Love waves. When guided in layers they are referred to as Lamb waves, Rayleigh–Lamb waves, or generalized Rayleigh waves. Rayleigh waves are characterized by elliptical motion perpendicular to the surface. In the near surface, this motion is “retrograde”, meaning that is counter-clockwise when the propagation is left-to- right. At depth, the motion can reverse to propagate. Locating the Epicenter: The epicenter of an earthquake is determined using the differences in arrival times of the primary or P waves and secondary or S waves. At least three records from properly spaced seismic stations forming an open triangle and with synchronized timing system are required for accurate determination of the epicenter. The most common graphical technique is the circle method. With three stations and three distances, the epicenter can be pin-pointe. Circles are drawn on a map of known scale using the location of recording stations as centers and computed epicentral distances at each station as radii. The common intersection of the circles drawn locates the earthquake epicenter. Quantification of Earthquake: (Intensity and Magnitude): Earthquake size is expressed in several ways: Qualitative or non-instrumental measurement and Quantitative or instrumental measurement.  The intensity of an earthquake at a location is a number that characterizes the severity of ground shaking at that location by considering the effects of the shaking on people, on manmade structures, and on the landscape. Instrumental intensity is the frequency-dependent spectrum based seismic intensity. It is calculated basically from the integration of the square values of spectral acceleration ordinates. Spectral acceleration is a measure of the maximum force experienced by a mass on top of a rod (structure) having a particular natural vibration period. Observational Intensity: Another way to measure the strength of an earthquake is to use the observations of the people who experienced the earthquake, and the amount of damage that occurred, to estimate its intensity. In seismology,  macroseismic means a classification of the severity of ground shaking on the basis of observed effects in a limited area.  microseismic is defined as a faint earth tremor caused by natural phenomena. The term is used to refer to the dominant background seismic noise signal on Earth, which are mostly composed of Rayleigh waves and caused by water waves in the oceans and lakes. Magnitude: Magnitude is the method of describing the strength of an earthquake based on instrumentally derived information and correlates strength with the amount of total energy released at the earthquakes’ point of origin. It is calculated mathematically using the amount and duration of movements that ground vibration causes on the needle of standard seismograph. Magnitude is a quantitative measure of earthquake size and fault dimensions. It is based on the maximum amplitudes of body or surface seismic waves. The first attempts to define magnitude scales were made in Japan by Wadati and in California by Richter in the 1930s. Most common magnitude scales: 1. Local or Richter magnitude (ML): measures the maximum seismic wave amplitude A (in microns) recorded on standard Wood-Anderson seismographs located at a distance of 100 km from the earthquake epicentre. 2. Body wave magnitude (mb): measures the amplitude of P- waves with a period of about 1.0 second, i.e. less than 10-km wavelengths. This scale is suitable for deep earthquakes that have few surface waves. 3. Surface wave magnitude (Ms): is a measure of the amplitudes of LR - waves with a period of 20 seconds, i.e. wavelength of about 60 km, which are common for very distant earthquakes, e.g. where the epicentre is located at more than 2,000 km. MS is used for large earthquakes. 4. Moment magnitude (Mw): accounts for the mechanism of shear that takes place at earthquake sources. It is not related to any wavelength. As a result, Mw can be used to measure the whole spectrum of ground motions. Richter magnitude ML exhibits several limitations. It is applicable only to small and shallow earthquakes in California and for epicentral distances less than 600 km. It is, therefore, a regional (or local) scale, while mb , MS , and MW are worldwide scales. Seismicity:  is the study of how often earthquakes occur in a particular area, which types of earthquakes occur there, and why.  more specifically, it refers to the measure of the frequency of earthquakes in a region—for example, the number of earthquakes of magnitude between 5 and 6 per 100 square km. The main factors affecting earthquake shaking intensity are earthquake depth, proximity to the fault, the underlying soil, and building characteristics - particularly height. The Philippine Archipelago lies between two major tectonic plates of the world: northwestward moving Pacific Plate & the oceanic parts of the slower-moving Eurasian Plate. Seismicity and tectonics of the Philippine Islands: Near the eastern Philippines the westward subduction of the Philippine Sea plate occurs:  along the Philippine Trench  in a localized zone near the western edge of the Benham rise. Most earthquake prone La Union and Pangasinan are prone to earthquakes, especially the deep-focused ones, due to the Manila Trench while Surigao del Sur and Davao Oriental have earthquake hazards due to Philippine Trench and nearby active faults. Location where do most earthquake occur: Six of the seven largest Philippine earthquakes since 1901 with magnitude almost 8.0 Mw or higher were in Mindanao: 1913,1918, 1924, 1943, 1972, and 1976. These areas are near the Cotabato Trench and the southern portion of the Philippine Trench.  Note: A trench is a type of excavation or depression in the ground that is generally deeper than its width, and narrow compared with its length. In geology, trenches are created as a result of erosion by rivers or by geological movement of tectonic plates. In particular, ocean trenches are a feature of convergent plate boundaries, where two or more tectonic plates meet. At many convergent plate boundaries, dense lithosphere melts or slides beneath less-dense lithosphere in a process called subduction, creating a trench. Major Philippine Faults: Faults showing signs or documented history of recent displacements are called Active Faults. The major active Philippine faults are: 1. Philippine Fault  extends 1200 km from Lingayen Gulf in Luzon to Davao Gulf, South of Mindanao (left-lateral strike-slip). 2. Bangui Fault  extends for more than 300 kms and slices NW-SE direction in northern part of the Central Cordillera from Bangui Bay and extends southward to mark the boundary between the Cordillera and the Cagayan Basin (right lateral strike-slip). 3. East Luzon Transform Fault  about 50 to 70 km long trending E-W offshore north of Polilio Island (left- lateral strike-slip). 4. San Antonio Fracture Zone  located north of Subic Bay beneath the northern apron Natib Volcano. 5. Taal Fracture Zone  NE-SW trending fracture zone passing Northern Mindoro, extending across the Verde Island Passage through Taal Volcano and the eastern lobe of Laguna de Bay. 6. Antique-Tablas Lineament  Marks the boundary between the Manila and Negros-Sulu trench arc system. 7. Mindanao Fault  400 km, NW-SE trending fault from Sindangan Valley, Northern Zamboanga to Cotabato. The major Plates of the earth’s surface are: 1. Eurasian Plate 2. Pacific Plate 3. Indo-Australian Plate 4. American Plate 5. African Plate 6. Antarctic Plate Other Plates are: 1. Philippine Plate 2. Fiji plate 3. Nazca Plate 4. Cocos Plate 5. Caribbean Plate Types of Earthquake Hazards: Hazard is generally measure in more physical units: energy, shaking strength, depth of water inundation, etc. 1. Primary Earthquake Hazards a) Ground Motion/Shaking  The Earth shakes with the passage of earthquake waves, which radiate energy that had been "stored" in stressed rocks, and were released when a fault broke and the rocks slipped to relieve the pent-up stress.  The strength of ground shaking is measured in the velocity & acceleration of ground motion, the frequency content of the shaking and how long the shaking continues (duration). b) Landslides Landslides, in and of themselves, constitute a major geologic hazard. Landslides are frequently triggered by strong ground motions. They are an important secondary earthquake hazard. Landslide include a wide range of ground movement, such as:  Rock falls  Deep failure of slopes  Shallow debris flows  c) Liquefaction Soil liquefaction is a phenomenon in which the strength and stiffness of a soil is reduced by earthquake shaking or other rapid loading. Liquefaction and related phenomena have been responsible for tremendous amounts of damage I n historical earthquakes around the world. Liquefaction occurs in saturated soils. The consequences to structures and utilities of earthquake-induced liquefaction include:  Non-uniform and differential settlement of structures often resulting in cracking.  Loss of bearing support.  Flotation of buried structures such as sewer lines, tanks, and pipes.  Strong lateral forces against retaining structures such as seawalls.  Lateral spreading (limited lateral movement).  Lateral flows (extensive lateral movement). d) Surface Rupture Surface rupture is an offset of the ground surface when fault rupture extends to the Earth's surface. Any structure built across the fault is at risk of being torn apart as the two sides of the fault slip past each other. Normal- and reverse- (collectively called dip-slip) faulting surface ruptures feature vertical offsets while strike-slip faulting produces lateral offsets. Many earthquake surface ruptures are combinations of both. 2. Secondary Earthquake Hazards Secondary earthquake hazards are those that are caused by the primary hazards, and may often be more catastrophic. a) Tsunami A tsunami is a wave train, or series of waves, generated in a body of water by a disturbance that moves the whole water column. Earthquakes, landslides, volcanic eruptions, explosions, and even the impact of cosmic bodies, such as meteorites, can generate tsunamis. Tsunamis can impact coastlines, causing devastating property damage and loss of life. Large earthquake (>M 6.5) can generate tsunami. Two types of tsunami:  Local Tsunami – are confined to coasts within a hundred kilometers of the source usually earthquakes and a landslide or a pyroclastics flow. It can reach the shoreline within 2 to 5 minutes.  Teletsunami – (also called an ocean-wide tsunami, distant tsunami, distant-source tsunami, far-field tsunami, or trans-ocean tsunami) is a tsunami that originates from a distant source, defined as more than 1,000 km (620 mi) away or three hours' travel from the area of interest, sometimes travelling across an ocean. It can travel from 1 to 24 hours before reaching the coast of the nearby countries. b) Seiche A seiche is a standing wave in an enclosed or partially enclosed body of water. Seiches are standing waves with longer periods of water- level oscillations (typically exceeding periods of three or more hours). Triggered by earthquake waves, seiches and seiche-related phenomena have been observed on lakes, reservoirs, swimming pools, bays, harbors and seas. The key requirement for formation of a seiche is that the body of water be at least partially bounded, allowing the formation of the standing wave. Difference bet. tsunami and seiche: A tsunami is a sea wave that results from large-scale seafloor displacement caused by a large earthquake, major submarine slide, or exploding volcanic island. A seiche is a series of standing waves in a fully- or partially-enclosed body of water caused by earthquakes or landslides.  c) Flooding Tsumamis generated by great earthquakes on subduction zone faults can flood coastal zones. Earthquake induced damage to levees, dikes, can also lead to flooding of a rivers natural flood plain. The failure of dams can lead to catastrophic floods from the rapid emptying of reservoirs, potentially drowning downstream communities. d) Fire Fire has long been recognized as a major hazard following earthquakes. Earthquakes would often upset burning candles, lamps, stoves and fireplaces (with dangerous fuels common). Ruptured gas lines and arcing electrical wires are the most common sources of ignition. In addition, earthquakes can block access to firefighting equipment, and damage fire-fighting water supplies, making fighting the blazes, very challenging. The 1995 Kobe Japan Earthquake highlighted the danger of urban fires following earthquakes. The fires consumed a combined area of 4,500 square meters and 5,500 buildings were lost to the fires. Seismic Hazard Assessment This process of evaluating for the purpose of seismic design the likely characteristics of future earthquake ground motions in a given seismic area is a critical step in the seismic design of structures called seismic hazard assessment. The characteristics of future earthquake ground motions are, for the most part, unpredictable and, hence, the selection of the ground motion characteristics for which structures should be designed constitutes a difficult and elaborate undertaking that involves the use of:  Historical information  Statistical data  Geological inferences  Probabilistic models  Empirical correlations  Engineering judgement Several parameters may be used to characterize earthquake ground motions, but the most common are:  Peak ground acceleration  Peak ground velocity  Response spectrum ordinates Identification of Seismic Sources a) Records from the hundreds of seismographic stations – that detect and record the occurrence of large earthquakes around the world provide quantitative data about the size, location, depth, and time of occurrence. b) Historical accounts of earthquake effects – are one useful way to detect the occurrence of past earthquakes, to estimate their magnitude, and to identify their geographical location. c) Geological evidence – also helpful to identify seismic sources and the frequency of past earthquakes. According to the plate tectonics and elastic rebound theories, earthquakes occur as a result of years of strain energy accumulation and the sudden relative motion between two tectonic plates. Semi probabilistic Seismic Hazard Evaluation As with any other type of seismic hazard assessment, the objective of a semi probabilistic seismic hazard evaluation is the estimation of a ground motion parameter such as peak ground acceleration, peak ground velocity, or a response spectrum ordinate to characterize the ground motions expected at a given site resulting from the earthquakes that can occur within a given time interval, in the vicinity of the site. Probabilistic Seismic Hazard Evaluation The worst earthquake disaster in the modern years occurred in North Sumatra at Banda Aceh. The great Sumatran earthquake occurred on the 26th December 2004, measuring at 9.3 on the Richter Scale, had created tsunami that killed 283,100 people from surrounding countries, including Malaysia with 68 people died. Earthquake Mitigation Mitigation means reducing risk of loss from the occurrence of any undesirable event. We cannot prevent natural earthquakes from occurring but we can significantly mitigate their effects by identifying hazards, building safer structures, and providing education on earthquake safety. By preparing for natural earthquakes we can also reduce the risk from human induced earthquakes. Preparedness refers to activities we do prior to an earthquake to be ready to respond to and recover from significant ground shaking. To begin preparing your home and family:  Identify potential hazards in your home and begin to fix them.  Create a disaster-preparedness plan.  Create disaster kits.  Identify your building's potential weaknesses and begin to fix them.  Protect yourself during earthquake shaking.  After the quake, check for injuries and damage.  When safe, continue to follow your disaster-preparedness plan. Earthquake preparedness for Government agencies and Tribes The Earthquake and Tsunami Program is responsible for supporting all governmental agencies and tribes to ensure the protection and safety of the populace in the event of an earthquake. Planning activities will vary by jurisdiction but should include the following: Communication, Shelters, Evacuation Plans, Resources and Inventory, Emergency Workers, Volunteers, Training, Access and Functional Needs population, Non- Government Organizations, Multi-Agency Coordination. Disaster Management Disaster Management can be defined as the organization and management of resources and responsibilities for dealing with all humanitarian aspects of emergencies, in particular preparedness, response and recovery in order to lessen the impact of disasters. A disaster is any occurrence that causes widespread distress and destruction. The definition of disaster management isn’t about stopping such an event when it occurs. Rather, it is about reducing the impact of these events on a company or community. When you don’t create a plan to deal with disasters, you could end up having to deal with lost revenue and massive human casualties. Disaster management covers a whole range of events, including communication failures, public disorder, terrorism, natural disasters and artificial disasters like electrical fires and industrial sabotage. A disaster is basically the difference between the sum total of the vulnerability a business or community has to a hazard and the actual occurrence of the hazard and the capacity of the community or business to handle that hazard. Three major goals of Disaster Management 1. Creating a more durable and effective recovery 2. Planning proactively to mitigate the risks faced by a business 3. Reducing the loss suffered via more effective planning and response efforts. 8 types of disaster: 1. Terrorist attacks 2. Rumours 3. Workplace violence 4. Organizational misdeeds 5. Malevolence 6. Confrontation 7. Technological crises 8. Natural disasters 5 Phases to Disaster Management: 1. The Prevention of the Disaster This is the phase where the human hazard of the disaster is prevented. It is typically used when you are dealing with terrorist attacks and natural disasters. 2. The Mitigation of the Disaster When you live an area prone to earthquakes, you could undertake some preventive measures, such as installing an earthquake valve that will shut off the supply of natural gas to a building in order to prevent a fire. You could also install seismic retrofits in houses and fit them with robust security systems. These mitigation measures can go a long way in reducing the negative impacts of disasters. It is best to be proactive long before the disaster hits. 3. Preparedness for the Disaster This phase is about readying the equipment and processes that will be implemented in the event of a disaster. These will be used to mitigate the impact of the disaster if it finally strikes. They can also be used to facilitate efficient responses in the event of an emergency. 4. Response to the Disaster This phase is an elaborate version of search and rescue and focuses on handling the humanitarian needs that must be fulfilled post-event. It involves providing people with rescue, medical aid, shelter, water and food, among other things. 5. Recovering from the Disaster This phase begins immediately after the disaster has subsided or when there is no longer an immediate threat to human life. The goal of this phase is to restore the normalcy that had prevailed in the population prior to the disaster in the quickest and most durable fashion. How to Prepare for Disaster as a Company 1. The Assessment of Risk Before you can plan for a disaster, you need to assess the risks involved in order to gain an intimate understanding of the environment and the circumstances under which you will be planning for that disaster. 2. The Planning Phase Here you should develop contingency plans or update existing ones base on the experience you gained during a previous disaster. 3. Testing and Training Disaster Management around the World  There is a focus on managing the risk of disaster in advance.  Corporate donations are shifting from cash to other resources as well.  Disaster preparedness is being integrated in development programs.  Rapid emergency response teams and emergency units are being developed.  Development banks and the private sector are becoming more involved.  Professional guidelines and standards are being improved.  Mitigation programs are being emphasized more than response programs. Lessons learned from previous/recent Earthquakes: 1. Structures Designed According To An Existing Code May Still Fail 2. Site-Soil-Structure Interaction Determines The Behavior of the Structure 3. The Characteristics Of The Structure Determine its Vulnerability To Earthquake Damage. Structures with serious irregularities in stiffness, mass or both are vulnerable to earthquake damage. These irregularities may either in the horizontal or vertical plane of the structure or both. 4. Trained Rescue Teams With Rescue Equipment Must Be At Hand For Post Rescue Operations. Although a number of examples of people surviving more than a week in the debris of collapsed buildings have been noted, survival of large number of people buried in the debris is highly dependent on their being extracted as fast as possible. 5. Structures Which Have Survived Major Earthquakes Need To Be Assessed For Undetected Damage. As previously mentioned, structures which have undergone a major earthquake often have a longer periods of vibration after the earthquake. This is indicative of loss of stiffness resulting from possible damage. 6. Structures Designed Under Older Building Codes Need To Be Reassessed In The Light Of Contemporary Knowledge. The bulk of structures either heavily damaged or collapsed in both Mexico City and San Francisco were those which were designed by older codes and which were not retrofitted to conform to contemporary knowledge or were only partially retrofitted.