Earthquakes Chapter 3 PDF

Earthquakes Internal Processes  An earthquake is the vibration of Earth produced by the rapid release of energy. – Energy released radiates in all directions from its source, the. – The surface located directly above the focus is the. – Energy released is in the form of. – Global...

Earthquakes Internal Processes  An earthquake is the vibration of Earth produced by the rapid release of energy. – Energy released radiates in all directions from its source, the. – The surface located directly above the focus is the. – Energy released is in the form of. – Globally, earthquakes are monitored using sensitive devices, the.  Earthquakes usually associated with large fractures in Earth’s crust called faults. Typically earthquakes occur along preexisting faults that formed in the distant past along zones of weakness in Earth’s crust. Most of the motion along faults can be explained by plate tectonics. It is along faults associated with plate tectonics that most earthquakes occur.  As rock is deformed, it bends, storing elastic energy. Once strained beyond its breaking point, the rock cracks (rupture), releasing the stored-up energy in the form of earthquake waves.  What is the Elastic Rebound Theory? Explains how energy is stored in rocks – Rocks bend until the strength of the rock is exceeded – Rupture occurs and the rocks quickly rebound to an undeformed shape – Energy is released in waves that radiate outward from the fault The phenomenon of elastic rebound Damage from the 1989 Loma Prieta earthquake in California section of Hanshin Expressway, eastern Kobe, Japan. Earthquake locations Where Do Earthquakes Occur and How Often? ~80% of all earthquakes occur in the circum-Pacific belt – most of these result from convergent margin activity – ~15% occur in the Mediterranean-Asiatic belt – remaining 5% occur in the interiors of plates and on spreading ridge centers – more than 150,000 quakes strong enough to be felt are recorded each year  Earthquake Locations World seismicity, 1979–1995. Color of symbol indicates depth of focus. Image courtesy of U.S. Geological Survey Types of Seismic Wave Primary (P) wave A type of seismic wave that involves alternating compression and expansion of the material through which it passes. Secondary (S) wave A seismic wave that involves oscillation perpendicular to the direction of propagation. S wave An earthquake wave, slower than a P wave, that travels only in solids. Long (L) waves These earthquake-generated waves travel along the outer layer of Earth and are responsible for most of the surface damage. L waves have longer periods than other seismic waves. What are Seismic Waves? Response of material to the arrival of energy fronts released by rupture Two types: – Body waves P and S – Surface waves R and L Body Waves: P and S waves Body waves – P or primary waves fastest waves travel through solids, liquids, or gases compressional wave, material movement is in the same direction as wave movement – S or secondary waves slower than P waves travel through solids only shear waves - move material perpendicular to wave movement  Surface Waves: R and L waves Surface Waves – Travel just below or along the ground’s surface – Slower than body waves; rolling and side-to-side movement – Especially damaging to buildings  Locating the Epicenter (B) Triangulation using data from several seismograph stations allows location of an earthquake’s epicenter (A) Difference in times of first arrivals of P waves and S waves is a function of the distance from the earthquake focus Seismographs record earthquake events At convergent boundaries, focal depth increases along a dipping seismic zone called a Benioff zone Frequency of Earthquakes of Various Magnitudes The Economics and Societal Impacts of EQs Damage in Oakland, CA, 1989 Building collapse Fire Tsunami Ground failure  Large earthquakes occurs near a large population center. It is most destructive natural forces on Earth. Buildings collapse, gas lines rupture causing numerous fire, and people die. Damage caused by earthquakes is measurable. : a measure of the degree of earthquake shaking at a given locale based on the amount of damage. : an estimate of the total energy releases during an earthquake, based on seismic record. How are the Size and Strength of an Earthquake Measured? Intensity – subjective measure of the kind of damage done and people’s reactions to it – isoseismal lines identify areas of equal intensity Modified Mercalli Intensity Map – 1994 Northridge, CA earthquake, magnitude 6.7 ‫‪Magnetometer A sensitive instrument used to measure the intensity of‬‬ ‫‪Earth’s magnetic field at various points.‬‬ ‫‪Mercalli intensity scale A 12-point scale developed to evaluate‬‬ ‫‪earthquake intensity based on the amount of damage to various structures.‬‬ ‫الوصف‬ ‫الشدة‬ ‫ال يشعر بها إال عدد قليل جدًا من الناس وحتت ظروف خاصة‪.‬‬ ‫‪I‬‬ ‫يشعر بها عدد قليل من الناس فقط يف حالة السكون وخاصة يف الطوابق العليا من األبنية وقد تتأرجح برفقق األجسقا‬ ‫‪II‬‬ ‫املتدلية‪.‬‬ ‫يشعر بها بشكل واضح األشخاص املتواجدون يف داخل األبنية وبشكل خاص يف الطوابق العليا منها ولكن العديقد مقن‬ ‫‪III‬‬ ‫الناس ال مييزونها على إنها زلزال‪.‬‬ ‫يشعر بها العديد من األشخاص املتواجدين داخل األبنية خالل النهار وقليل من األشقخاص يف ااقار ‪.‬تقوق بعق‬ ‫‪IV‬‬ ‫األشخاص النائمني‪ ،‬تهتز األواني والنوافذ واألبواب‪ ،‬حتدث اجلدران أصوات تشقق تولد ضجة تشبه اصقطدا عجلقة‬ ‫كبرية يف البناء‪ ،‬تتحرك العجالت الواقفة بشكل واضح‪.‬‬ ‫يشعر بها اجلميع وتوق العديد من النائمني‪ ،‬تتكسر بع األوعية والنوافذ وما شابه ذلك‪ ،‬يتشققق اجلقص يف بعق‬ ‫‪V‬‬ ‫املناطق‪ ،‬تنقلب األجسا غري الثابته‪.‬تالح بع التأثريات على األشجار واألعمدة واألجسا الطويلقة األخقر ‪.‬ققد‬ ‫تتوقف الساعات البندولية‪.‬‬ ‫األثاث الثقيل حاالت عديدة من سقوط‬ ‫يشعر بها اجلميع وقد يفزع منها العديد ويهربون خار األبنية‪.‬يتحرك بع‬ ‫‪VI‬‬ ‫اجلص وحتطيم املداخن‪.‬األضرار قليلة‪.‬‬  ‫يهرع اجلميع خار األبنية واألضرار بسقيطة يف األبنيقة ذات التمقاميم اانشقائية ا كمقة‪.‬أضقرار قليلقة إ‬ ‫‪VII‬‬ ‫متوسطة يف األبنية االعتيادية اجليدة ‪ ،‬أضرار واضحة يف األبنية الضعيفة ذات التماميم الرديئة‪.‬تتكسر بعق‬ ‫املداخن‪.‬يالحظها األشخاص الذين يقودون سياراتهم‪.‬‬ ‫األضرار قليلة يف األبنية ذات التماميم اانشائية ا كمة‪.‬األضرار واضحة يف األبنية العادية مع انهيار جزئي‬ ‫‪VIII‬‬ ‫وهي واضحة بشكل كبري يف األبنية واملداخن ذات الرتاكيب الضعيفة‪.‬تتأثر ألواح اجلدران بعيداً عن ااطارات‪.‬‬ ‫تتساقط األعمدة واجلدران ‪ ،‬انقالب األثاث الثقيل‪ ،‬تناثر الرمل والطني بكميات قليلة‪.‬تغريات يف ميقا اببقار‬ ‫‪ ،‬ارتباك األشخاص الذين يقودون سياراتهم‪.‬‬ ‫األضرار كبرية حتى يف األبنية ذات الرتاكيب اااصة‪ ،‬تنحرف األبنيقة ذات ايياكقل ا كمقة عقن وضقعها‬ ‫‪IX‬‬ ‫الشاقولي‪ ،‬األضرار جسيمة يف األبنية الكبرية مع انهيار جزئي‪ ،‬حتطم بع األساسات‪ ،‬تشقق األرض وتكسقر‬ ‫األنابيب املوجودة حتتها‪.‬‬ ‫تتحطم بع الرتاكيب ااشبية اجليدة‪ ،‬تتشقق األرض بشكل كقبري مقع اانقاء السقكك ا ديديقة‪.‬حتمقل‬ ‫‪X‬‬ ‫انزالقات أرضية واضحة على ضفاف األنهار واملنحدرات ا ادة‪.‬تمعد امليا فوق الضفاف‪.‬‬ ‫يممد عدد قليل جداً من األبنية‪ ،‬تتحطم اجلسور‪ ،‬حتدث تشققات كبرية يف األرض‪ ،‬إصابة مجيقع األنابيقب‬ ‫‪XI‬‬ ‫املمدة حتت األرض وبشكل كامل‪.‬تنزلق األرض يف منطقة ايزة‪.‬تنحين سكك ا ديد بشكل واضح وكبري‪.‬‬ ‫دمار تا وشامل‪.‬ميكن مالحظة املوجات على سقطح األرض‪.‬يتشقو مقد الرايقا واألفقق‪.‬تققذف األجسقا يف‬ ‫‪XII‬‬ ‫ايواء‪.‬‬  Magnitude of an earthquake is measured by scale :a logarithmic scale used to express the total energy released by an earthquake. Its values typically fall between 0 and 9, with each increase of 1 representing a 10-fold increase in energy. How is an Earthquake’s Epicenter Located? Seismic wave behavior – P waves arrive first, then S waves, then L and R – Average speeds for all these waves is known – After an earthquake, the difference in arrival times at a seismograph station can be used to calculate the distance from the seismograph to the epicenter. Earthquake Magnitudes and Expected World Incidences Richter Estimated Effects Near Epicenter Magnitudes number/year 8.0 Great earthquakes. Causes extensive destruction to communities near epicenter  (tsu = harbor, nami = waves): series of catastrophic waves generated by earthquakes, mass movements above or below water, volcanic eruptions and other underwater explosions, landslides, large meteorite impacts and testing with nuclear weapons at sea.  An earthquake that occurs under the ocean has the potential to form a tsunami. – Tsunami is a Japanese word with “tsu” meaning harbor and “nami” meaning wave. Not every earthquake will form a tsunami, the movement must result in the VERTICAL DISPLACEMENT of water. That is: if a piece of the ocean floor moves either up or down (see the Extension and Compression fault examples) the ocean water will be rapidly displaced and this will form waves at the surface. If two pieces of crust slide past each other (see Transform fault example) there is no vertical movement of the crust or the overlying water and a tsunami will not form. Seawalls Seawalls have been constructed on many beaches not only for protection against tsunami’s but also the hazards of large storm waves. Seawalls are designed to make waves break early (before the shoreline), therefore dissipating their energy before they reach the shore. Some walls are designed to build up the shoreline to prevent waves from over topping the shore and flowing into residential areas.  : geological phenomena which include wide range of ground movement, such as rock falls, deep failure of slopes and shallow debris flows.  Can Earthquakes be Predicted? Earthquake Prediction Programs – include laboratory and field studies of rocks before, during, and after earthquakes – monitor activity along major faults – produce risk assessments  Can Earthquakes be Controlled? Graph showing the relationship between the amount of waste injected into wells per month and the average number of Denver earthquakes per month Some have suggested that pumping fluids into seismic gaps will cause small earthquakes while preventing large ones Seismicity map of Kuwait (Source KISR 2010) ‫النشاط الزلزالي اإلقليمي حول الكويت‬ Earthquakes Safety Rules THANK YOU!