Planet Earth Course (GEOL 110) - Natural Hazards & Risk Management - PDF

Planet Earth Course (GEOL 110)- BLT form Chapter 5: Natural Hazards and risk management Delivery method: mainly online Dr. Dalal Alshamsi Geology Department, College of Science United Arab Emirates University Outline: Earthquakes and their associated hazards (Faults, Tsunami, aftershoc...

Planet Earth Course (GEOL 110)- BLT form Chapter 5: Natural Hazards and risk management Delivery method: mainly online Dr. Dalal Alshamsi Geology Department, College of Science United Arab Emirates University Outline: Earthquakes and their associated hazards (Faults, Tsunami, aftershock, liquefaction, Landslides). Coastal erosion Floods Karsts (cavities) Droughts and desertification Volcanoes Risk management of each hazard  Session 1: Earthquakes (seismic activity) Earthquakes Many of the world’s largest cities (like: Istanbul, Tokyo, Jakarta) are located near plate boundaries that represent zones of frequent earthquake activity. During the 20th century, over 2 million people were killed by earthquakes and associated phenomena (Faults, Tsunami, aftershock, liquefaction, Landslides). Earthquakes theory (Elastic rebound theory) Elastic Rebound Theory: https://docplayer.net/57728445-31-may-16-summer-session-horst-rademacher-lect-3-earthquake-faults.html When the two sides of tectonic plates are active and slowly moving in different directions and the stress becomes too great, then the rocks separate (faulted) and an earthquake results. After that the rock returns to its undeformed state. Earthquake faults http://researchgate.net http://naturldisasterintheworld.blogspot.com/2015/03/what-is-earthquake-earthquake-also.html Earthquake Lingo The focus of an earthquake is the point on the fault where break (rupture) first occurs. Focus occurs in the subsurface. The epicenter is the point at the surface directly above the focus. Focus and epicenter knowledge is useful in earthquake risk management! Earthquake waves (seismic waves) There are two main types of The body waves include: waves: 1. Primary wave = P-wave (it arrives first because it is the fastest) 1. Body waves (propagate in the 2. Secondary wave = S-wave (arrives subsurface) next) 2. Surface waves (propagate on the surface) The surface waves in general are the slowest waves and so they arrive at the end. Surface waves include: 1. Love waves 2. Rayleigh waves The seismograph instrument records the seismic waves In the seismogram below, the primary wave (P) arrives first, then secondary wave (S), and finally the surface waves.  How to minimize the earthquake risk in the surrounding areas? Each type of seismic waves travels with a different velocity away from the focus, therefore each wave arrives, at measuring stations, at different time. The difference in time of arrival can be used to calculate the distance to the focus or epicenter, and so alarming the people in the surrounding cities by the expected time the earthquake might arrive to their places. The only people who are not able to predict the earthquake arrival time are who live in the first city the earthquake attacks! Earthquake is measured in two scale: Richter scale Mercalli scale Measures the energy of the Measures the effect of earthquake physically earthquake on people and Quantified scale buildings Descriptive scale  Richter scale Richter scale starts from 320 (magnitude =1) to 328 (magnitude =9). The energy is increasing by a power on 32 in each upper level. You can observe that energy of Richter magnitude 5 is around one million, but the energy of Richter magnitude 6 is around 33 million! So the differences between two magnitudes is huge! Mercalli scale It is inaccurate scale because it depends on the infrastructure of the city and the descriptions given by witnesses. Two earthquakes of similar energy on Richter might be with different scales on Mercalli! Because a developed country will have less effects on buildings than a developing country. Hazards associated with earthquakes The probable associated hazards with earthquakes are: Faults, Tsunami, aftershock, liquefaction and Landslides. Fault is displacement in rock beds. Tsunami is not a tidal wave, but a serious of huge waves caused by earthquakes, and building them selves higher and higher from the epicenter to the coast. Hazards associated with earthquakes Aftershock is a smaller earthquake following the major bigger earthquake. Aftershock has less energy than Haiti the major earthquake. It happens if the earth doesn’t aftersock release the full stress in the major earthquake. main shock Hazards associated with earthquakes Liquefaction is the escape of water from an aquifer (groundwater reservoir) to the surface because of shaking the earth’s surface in an earthquake. This will cause a slide and damage to buildings. Liquefaction happens only if aquifer occurs in the earthquake zone.  Hazards associated with earthquakes Landslide is mass wasting from https://gulfnews.com/uae/weather/weather-in-uae-heavy-rain-floods-wadis-around-jebel-jais-in-rak-1.2294647 a slope due to seismic activities or other reasons like water and gravity effects. Landslides in Jais Mountain in Ras Al Khaima because of raining water How to minimize the risk of landslides? There are several techniques to manage the risk of landslides like: Wire mesh, Concrete cover and Retaining wall  Session 2:  Coastal erosion  Floods  Karsts (cavities)  Droughts and desertification  Volcanoes Coastal erosion Both human activities and natural processes How to minimize the risk of are at work shaping the coastlines. coastal erosion? Natural processes include mainly wave action. Three types of structures may Human interference includes building of be built on or near coasts: structures along the coastline, or modifying  Seawalls the coast to improve facilities.  Breakwaters Why is coastal erosion considered as risk?  Groins Because it might damage the nearby constructions and cause sea-water intrusion to the soil and aquifers which probably result is salty soil and salty groundwater. Coastal erosion Seawalls Breakwaters Groins  The main aim of building a  Breakwater is a fixed or  A groin is a pier of rocks seawall is to minimize the floating construction or a wooden barrier energy of the sea waves aimed to absorb the jutting out from the beach and provide a protective energy of waves and into the sea, built to cover for the more easily therefore protect the prevent longshore eroded coastal sediments coast. currents from eroding the and rocks.  It is different from a beach sand.  The seawall is built on the seawall in that it doesn’t coast so it covers the cover the coastline. coast line. Abu D ater Break habi w Floods In dictionary flooding is submerging of normally dry land with a large amount of water. Causes of flooding: Effects of flooding: Heavy precipitation  Loss of life  Capacity of ground to absorb  Damage to buildings and roads water  Evaporation rate  Destruction of crops Natural characteristics of river  Collapse of river banks banks  Release of toxic materials from damaged Human modifications of land facilities  Floods How to minimize the risk of floods? Some techniques are used to minimize the effects of floods like building levees, diversion canals and dams.  Levees are raised river banks.  Diversion canals are redirecting excess water to purpose-built canals. Diversion canals in Manila.  Dams have two benefit: controlling the floods and storing the excess water for future use. Mount Morris Dam in New York. Karsts (cavities) Karst or cavities are usually formed after dissolution caused by chemical weathering in limestone (carbonate rocks). February 2007, Guatemala It is a slow process that might be caused by acid raining effect on limestone. October 2018, Hafit Mountain Karsts (cavities) Karsts effects: How to reduce the risks of 1. Buildings collapsing karsts? 2. Life loss Preliminary site evaluation using geophysical methods could assess 3. Economic drain in construction site selection to avoid karsts risk areas. Karsts example: Shaikha Salama Mosque in Al Ain The first phase: (1981- 2006). The mosque was destroyed in 2007 after exploring some First phase of the collapses due to the underlined mosque karsts. These karsts were treated geo- technically and the mosque was rebuilt and the re-opened in 2012. The re-built mosque Karsts protection in Abu Dhabi Geophysical investigation in any cite is compulsory before going through construction processes in the Emirate of Abu Dhabi, to avoid the possible risks of karsts formation. This law was enacted by an encourage of Professor Haydar Bakr from Geology Department, UAE, who spreaded out the awareness of the significance of Geophysical Professor Haydar Bakr from Geology Department in studies before construction works the UAEU, who was the reason behind legislation the law of “Geophysical studies in any cite is compulsory are started. before going through construction processes in the Emirate of Abu Dhabi”. Droughts and desertification Drought Desertification A drought is an extended period of Frequent droughts could lead to months or years when a region notes permanent desertification. a deficiency in its water supply. Human activities also like deforestation Drought is temporary case and ends and urbanization cause desertification. when water supply comes back. Desertification is considered as permanent case and defined as the conversion of crop Drought risk management could only productive land to desert. be through water consumption Desertification risk reduction could only management. applied at the early stages of desertification. Volcanoes Volcanoes occur usually at known places in the world. A majority of active volcanoes are located at convergent plate boundaries. To minimize the risk of volcanoes, scientists shall estimate the risk area around each active volcano. The risk area differ according to each volcano characteristics like: lava viscosity, silica content, temperature and volcanic ash quantity. Examples of volcanoes: Fuji in Japan and Cleveland in Alaska. End of Chapter 5 And Planet Earth Course