Human Causes of Earthquakes INTRODUCTION

Transcription

1 1 EPSC 330: Presentation Summary Human Causes of Earthquakes Ridwan Ahmed & Beshr Alalawi Definition of an Earthquake INTRODUCTION An earthquake is the shaking of the surface of the Earth, resulting from the sudden release of energy in the Earth's lithosphere that creates seismic waves. The shaking motion of an earthquake is the result of a sudden release of energy. Earthquakes are caused when stress, building up within rocks of the earth's crust, is released in a sudden jolt. Rocks crack and slip past each other causing the ground to vibrate. Cracks along which rocks slip are called faults. They may break through the ground surface, or be deep within the earth. Consequences of Earthquakes They can cause - Tsunami - Landslides - Shaking, rupture - Liquefaction: Liquefaction is when sediment grains are literally made to float in groundwater, which causes the soil to lose all its solidity. - Fires : Rupturing of natural gas mains and water mains - Life loss - Financial losses Causes of Earthquakes - Natural Causes o Rockslides and volcanos: Prior to an eruption and as an eruption occurs, molten rock moves into a magma chamber under the volcano and then from the chamber to or toward the ground surface, where it often breaks through as lava, dust, ash and superheated gasses. The movement of magma and the eruption causes the ground to tremble and depending on the quantity of material that is moving, along with how explosive the volcano is, the earthquake can be often felt over a large area.

2 2 o Plate technics: The place where plates meet is called a fault or convergence zone and while the plates are in motion, the rock that is above the fault is solid rock. This means that the rock sticks on each side of the fault, even though the plates are moving. When the stress in the rock along the fault line gets too great for the rocks to bear, the rocks fracture or break. This sudden release of energy is felt as an earthquake. Ex. San Andreas fault. o Plate subduction: Both types of plate collisions cause earthquakes, however in subduction, the plate edge that is being forced beneath another plate is melted due to friction. Since the molten rock is lighter than solid rock, it tries to move upward. When and if it succeeds and breaks through the surface, it is a volcanic eruption. Ex. Ring of Fire. - Human Causes o Hydraulic Fracturing (Fracking) or Injection Wells o Dams & Reservoirs o Groundwater Extraction o Geothermal Power Plants o Construction Hydraulic Fracturing Definition of Hydraulic Fracturing A technique in which rock is fractured by a pressurized liquid. The process involves the high-pressure injection of 'fracking fluid' (primarily water, containing sand or other proppants suspended with the aid of thickening agents) into a wellbore to create cracks in the deep-rock formations through which natural gas, petroleum, and brine will flow more freely. When the hydraulic pressure is removed from the well, small grains of hydraulic fracturing proppants (either sand or aluminum oxide) hold the fractures open. How Does Hydraulic Fracturing Cause Earthquakes? Hydraulic fracturing increases seismic activity along dormant or previously unknown faults due to deep injection disposal of hydraulic fracturing flow back (which is a byproduct of hydraulically fractured wells) and formation brine. It is also believed that the chemicals stay underground and make their way to faults, adding lubrication that may lead to an earthquake. Benefits of Hydraulic Fracturing Allows to greatly increase the production of oil. Example: In 1984, Oklahoma s oil production was 168,385,000 barrels per year. In 2005, it dropped to 61,262,000 barrels per year. By 2013, it climbed back to 113,966,000 barrels. Oklahoma s Natural Gas Marketed Production in 1984 was 2,046,339 MMcf. In 2003, it had dropped to 1,558,155 MMcf. By 2013, it had risen to 2,143,999 MMcf.

3 3 The United States has surpassed Saudi Arabia and Russia in oil production and as of 2010, became the world s largest producer of natural gas. Regulations Hydraulic fracturing is under international scrutiny, restricted in some countries, and banned altogether in others (such as France). The European Union is drafting regulations that would permit the controlled application of hydraulic fracturing. Examples of Earthquakes Due to Hydraulic Fracturing An example of this can be seen in the state of Oklahoma in the United States. As fracking became more frequent in 2011, so did the number of earthquakes. In fact, in 2008 there were only about 12 earthquakes reported. In 2011, this number increased to more than 1,000 earthquakes just in one year. Dams and Reservoirs What Are Dams & Reservoirs? Dams are structures that are built on a river in order to retain water for one or more specific purposes (e.g. hydroelectricity generation). Reservoirs are formed behind a dam. A reservoir is a body of water that has been formed or modified by human activity for specific purposes, in order to provide a reliable and controllable water resource. How Do Dams & Reservoirs Cause Earthquakes? Earthquakes can be induced by dams. Globally, there are over 100 identified cases of earthquakes that scientists believe were triggered by reservoirs. This phenomenon is known as Reservoir-induced seismicity (RIS). RIS is related to the extra water pressure created in the micro-cracks and fissures in the ground under and near a reservoir. When the pressure of the water in the rocks increases, it acts to lubricate faults, which are already under tectonic strain, but are prevented from slipping by the friction of the rock surfaces. What Are the Benefits of Dams & Reservoirs? Dams provide a range of economic, environmental, and social benefits. Examples are recreational facilities, flood control, water supply, hydroelectric power, waste management, river navigation, and wildlife habitat. Example of Earthquakes Due to Dams & Reservoirs? The 2008 earthquake in Sichuan, China left over 70,000 dead and is believed to have been caused by the construction of the nearby Zipingpu Dam. This dam is located only a third of a mile away from a plate

4 4 tectonic fault line and geologists believe this added mass of the water caused the fault to slip sooner that it naturally would have. Groundwater Extraction What is Groundwater Extraction? Groundwater extraction is the process of taking water from a ground source, either temporarily or permanently. Except in areas where groundwater comes naturally to the surface at a spring (a place where the water table intersects the ground surface), we have to construct wells in order to extract it. If the water table is relatively close to the surface, a well can be dug by hand or with an excavator, but in most cases we need to use a drill to go down deep enough. How Does Groundwater Extraction Cause Earthquakes? It can be dangerous if extraction is done at a quicker rate than the underground reservoir can be recharged. In fact, if the water table drops too quickly near a fault, it could cause an earthquake. Example of Earthquakes Due to Groundwater Extraction? For example, in 2011, there was a 5.1 magnitude earthquake in Lorca, Spain that is believed to be caused by excessive groundwater extraction. The epicenter of this earthquake was close to the surface leading scientists to believe it was due to the groundwater extraction nearby. Geothermal Power Plants What is a Geothermal Power Plant? Geothermal power plants are used in order to generate electricity by the use of geothermal energy (the Earth's internal thermal energy). Hot water or steam is extracted from the Earth through a series of wells and feeds the power plant. How Does Geothermal Power Plants Cause Earthquakes? Under the surface is a rock called felsite you can think of it like granite; it's the heat source for the sandstone. But there's no water in the felsite, so they drill, then they pipe water under strong pressure and flow rate, to fracture the rock. This fracturing triggers earthquakes. Benefits of Geothermal Power Plants Not only is it a renewable type of energy but is also present in most areas, outperforming even some conventional sources in many aspects. - Good for the environment - Reliable source of energy

5 5 - High efficiency - Few movable parts Easy to maintain Example of Earthquakes Due to Geothermal Power Plants Geothermal power plants have been labeled as the cause of a massive 2006 mud volcano in Java (Indonesia), which displaced more than 30,000 people after a gas exploration project went awry. Another example is in the Salton Sea (San Andreas Fault), seismic activity has been seen to increase forming numerous small earthquakes.

6 6 Sources Hydraulic Fracturing. (n.d.). Retrieved April 08, 2018, from Govt, Energy Industry Accused of Suppressing Fracking Dangers. (n.d.). Retri eved April 08, 2018, from Patel, T. (2011, March 31). The French Public Says No to ' Le Fracking '. Retrieved April 08, 2018, from An overview of hydraulic fracturing and other formation stimulation technologies for shale gas production - Update EU Science Hub - European Commission. (2016, September 09). Retrieved April 08, 2018, from A review of recent studies of triggered earthquakes by artificial water reservoirs with special emphasis on earthquakes in Koyna, India. (2002, February 19). Retrieved April 08, 2018, from A Faultline Runs Through It: Exposing the Hidden Dangers of Dam-Induced Earthquakes. (n.d.). Retrieved April 08, 2018, from Benefits of Dams. (n.d.). Retrieved April 08, 2018, from Earle, S. (n.d.). Retrieved April 08, 2018, from groundwater-extraction/ Geothermal power plants. (n.d.). Retrieved April 08, 2018, from Harmon, K. (2009, June 29). How Does Geothermal Drilling Trigger Earthquakes? Retrieved April 08, 2018, from