GEOL 101 1nd Edition Lecture 29 Outline of Last Lecture I Locating earthquakes II Measuring earthquakes III Earthquake Hazards IV Earthquake Destruction Outline of Current Lecture I Secondary Hazards II Predicting Earthquakes III Preparing Earthquakes IV Earth s Interior V Physical Layers VI Discovering Earth s Interior Current Lecture Secondary Hazards Fire Often times Earthquakes will break cities water lines allowing fires to spread quickly Such was the case during the 1906 San Francisco earthquake o April 18 1906 estimated 7 9 MMS earthquake sourced along the San Andreas Fault o Despite being at 7 9 Mw the greatest loss of the life and property was due to the fire Disease With damaged infrastructure thousands of people displaced and homeless living in crowded unsanitary refugee camps disease outbreaks often follow earthquakes Especially prevalent in developing nations o January 12 2010 The 7 0 Mw magnitude Haiti earthquake not only crippled the city of Port au Prince but within 9 months there were over 2300 cases of Cholera and nearly 200 confirmed deaths from the disease These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute o Primary source of contracting the disease is unsafe drinking water Nuclear hazards One of the most tragic effects of the 9 0 Mw Japan earthquake is the continuing disaster at the Fukushima nuclear power plant While the earthquake itself did not significantly damage the nuclear plant the 46 ft high tsunami wave did the plant was protected by a seawall that would withstand a more typical 19 ft wave o The cooling system in the past was so damaged in addition to loss of power in region reactors began to overheat with the radioactive decay o Partial core meltdown of reactors 1 2 and 3 with fires and explosions in 1 4 The main concerns are radioactive caesium iodine and plutonium which At the peak of radiation release the core was releasing 400m Sv h which is roughly twice what the Chernobyl workers were dosed with o The Chernobyl core explosion released over 300 000 o So far only about 1 10 of the amount of radiation released from Chernobyl has been released from Fukushima While not as catastrophic as Chernobyl Fukushima is still rated as a level 7 major accident Major long term health risks cancer are expected in the immediate area Predicting Earthquakes We do not yet have accurate short term methods of predicting when and where an earthquake will strike There are some precursors such as o Foreshocks o Bizarre animal behavior o Changes in the ground water o Release of radon gas or methane from the ground Some of these have been useful in predicting past earthquakes however they do not always occur We do have good methods for making earthquake forecasts long term likelihood of where when and how big an earthquake might be hazard assessments We can study faults and earthquake history in an area to predict how often earthquakes happen in that area Data sources o Recent earthquakes data from seismometers o Ancient earthquakes data from the roc record or pale seismology Earthquake forecasts are given as probabilities Large faults such as the San Andreas don t continuously move but rather move in segments There are often times bends along the fault o This is where stress gets concentrated An area along the fault that has not had any earthquakes in a long time is called a seismic gap o This is where the fault has been locked for quite sometime o There is presumably a lot of strain building up within the seismic gap making it the most likely place to rapture We can also use long term studies to establish a recurrence internal the average time between earthquakes of a specific size along a fault Recurrence internals are also calculated as probabilities i e There is a 20 chance that an earthquake of 7 0 or higher will occur in the next 10 years Preparing Earthquakes There are a number of ways to prevent loss of life and property for those living in earthquakeprone areas Engineering earthquake resistant structures Emergency response protocol Tsunami warning systems Public education Most earthquake related deaths occur when buildings collapse In California buildings are designed to have a certain amount of give or ductility so that when buildings sway up down left right back front the material can bend instead of break Brick buildings are not resistant beneath the brick and mortar are rigid materials Flexible steel allows for more sway This earthquake resistance is still limited physical and economic factors to how strong we can make construction material Emergency response is critical during an earthquake if resource personnel know the hardest place hits they can allocate resources to save more lives Southern California has established a system called TriNet When an earthquake hits it shows them the intensity of ground shaking across the area and thus the areas to send first response teams Tsunamis are a major hazard along coastal areas particularly along the Pacific Ocean The Pacific Tsunami Warning Center in Hawaii tracks earthquakes around the Pacific rim and calculates arrival times of oncoming tsunami waves This gives Hawaiian coastal communities enough time to evacuate if a tsunami is coming Earth s Interior Prior to the turn of the 20th century very little was known about the interior of the earth The deepest well that has been drilled is 7 5 miles deep While impressive for a well it is still less than 1 of the entire distance to the core It has been through the study of Earthquake waves that scientists have been able to understand what s going on beneath us If the earth were a perfectly homogenous material we would observe seismic waves travel through at constant speeds and in straight lines This however is not the case It is observed that seismic waves travel faster with depth which is consistent with materials under increasing pressure This causes the seismic waves to refract bend instead of traveling in a straight line Some lines are also reflected back to the surface at certain depths The compositional layering of the planet most likely occurred early during formation when heavier elements sank to the center and lighter elements floated to the crust This process is known as chemical differentiation and has divided the earth in to three major compositional layers o Crust very thin outer layer that ranges in thickness of about 3 km at seafloor spreading