Understanding Earthquakes and Volcanoes: Key Concepts Explained

M O D U L E 5 : E A R T H Q U A K E S A N D V O L C A N O E S Logan Gruss 2/11/24

W H AT I S A N E A RT H Q U A K E ? • An Earthquake is defined as a ground shaking caused by the sudden and rapid movement of one block of rock slipping past along fractures in Earth’s Crust, called faults (Lutgens et al, 2021). The fault is typically locked due to the massive pressure exerted by the overlaying crust squeezing them shut. What triggers the earthquake is when differential stress builds to such a level that it overcomes the frictional forces holding the rock bodies together (Lutgens, et al, 2021). The hypocenter or focus is the point in which the rock slippage starts. • Earthquakes can happen very frequently, for example according to earthquake.usgs.gov there was over 40 earthquakes in the past day, all above a 2.5 magnitude, the most recent listed to the left (Latest Earthquakes, 2024).

W AV E S • When an earthquake releases built up energy this is in the form of “seismic waves.” The waves can travel through the lithosphere and Earth’s interior, moving in all directions like a ripple in a lake (Lutgens et al, 2021). The shaking that occurs during an earthquake are a result of these waves carrying energy that vibrates the material transmitting them. Although some of the epicenters are more difficult to discover than others, with the help of seismographs, even the smaller earthquakes can be detected from across the globe. By using a seismograph, data pictured below (Anss heliplots, 2024) scientist can track these waves and any changes that seem abnormal.

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I N T E N S I T Y V S . M A G N I T U D E • Intensity scale (example to the right, (Communications, 2021)) uses property damage to estimate the amount of ground shaking at a particular location, while magnitude uses data from seismographs to estimate the amount of energy released at an earthquake’s source (Lutgens et al, 2021). Intensity scales were used far before seismic ones, as you can determine the intensity visually rather than just through data points which were not available.

FA U LT S • Faults are fractures in the crust along which appreciable displacement has taken place (Lutgens et al, 2021). Scientists classify faults based on slip and dip angle. Dip-Slip faults move along the dip plane, while strike-slip faults move more horizontal (Lutgens et al, 2021). Oblique faults would show both a strike and dip slip. However, there are many other faults than just those described such as, reverse faults, normal faults, strike-slip faults, left-lateral strike- slip fault. A normal fault is a dip-slip when the hanging wall block moves down relative to the footwall block. Due to the downward motion this fault accommodates stretching of the curst (Lutgens et al, 2021). A reverse fault is when the hanging block wall moves up relative to the footwall (Lutgens et al, 2021). This is also commonly referred to as a thrust fault. A strike-slip fault is when dominant displacement is horizontal and parallel to the strike of the fault (Lutgens et al, 2021). The right or left lateral determination is found by which way the displacement is.

D E AT H S A N D D A M A G E • Earthquakes are a devastation force of nature that in some cases will tear the earth open and begin engulfing whatever was above. Without proper preparation earthquakes can do an unheard-of amount of damage in such a short amount of time. With most earthquake related deaths being in countries with a less ideal infrastructure leads one to believe the importance of building with the notion of earthquakes in mind. The only defense against an earthquake for a building is infrastructure made for an earthquake, and even then, it sometimes is not enough. However, data shows that earthquakes are not just dangerous to those regions, but also anywhere there is activity among the faults, such as the United States since colonial era (Lutgens et al, 2021). Earthquakes are detrimental to structures and with collapsing structures comes many deaths.

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C U R R E N T T H R E AT L E V E L • Earthquakes that damage structures occur 70-75 times across the globe. Here in Maine, we experience an average of 5 quakes per year (Maine Emergency, 2020). It is determined that forty-five states and US territories are at moderate to very high risk of earthquakes, Maine being a moderate case (Maine Emergency, 2020). Areas that would result in a high magnitude earthquake would • The map to the right will show the threat levels for different regions. We can determine that the regions in red, such as northern California, Oregon, and parts of Mexico that connect to California will be at the most risk of high magnitude quakes. This is due to the level of seismic activity being significantly higher near these faults. (Earthquake Danger Map, (n.d.))

FA U LT T H R E AT • The location mentioned on the previously slide, Northern California, will be the home of the San Andreas fault and the Hayward fault, which would be slip-strike faults, sometimes referred to as a “tectonic bomb” by US Geological Survey Scientists (Earthquake Danger Map, (n.d.)). I believe this is because this area is a major fault zone. Most earthquakes with high magnitude will originate from areas such as this one, and some are situated around volcanoes (Vergano, D. , 2021)

D E AT H S I N T H I S R E G I O N • The damage to this region would be catastrophic if a magnitude of 6+ were to strike. This is because the fault stretches a large portion of the state of California, which overtime has been rattling this area. The large population and weak ground from seismic activity would result in the collapse of structures and many people left under the rubble. Areas of mass population that require buildings, in areas of seismic activity, are always the most vulnerable target. • The threat of Earthquakes here in Maine is there, but minimal due to the fact that the seismic activity cause by the quakes is quite low and unnoticed.

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V O L C A N O E S • The planet has around 500 currently active volcanoes (Youtube, 2012). These can form in many ways ranging from breaking through a thin point in the crust, or form on a fault line. The shifting of plate tectonics is what forms the liquid rock or magma that would later escape the earth’s crust. This point of volcanic activity becomes a volcano when a fissure develops in the curst (Lutgens et al, 2021). The magma rises until it reaches the vent of the fissure. The volcanic cone we see is the excessive eruption of lava building up overtime and through periods (Lutgens et al, 2021). The depression we see in the center of a large volcano would have been formed by volcanic material building up on the edges. Volcanoes will usually take on two forms, Shield Volcanoes and strato volcanoes. A shield volcanoes is wider and has a slower lave flow, while the strato is much steeper and more explosive (Youtube, 2021).

T Y P E S • Shield- these are produced by an accumulation of fluid basaltic lavas and exhibit the shape of a broad, slightly domed structure that resembles a warrior’s shield, typically beginning on the ocean floor as seamounts (Lutgens et al, 2021). The shape is determined by the hot fluid lava that traveled far and fast from the vent. Later in its life the volcano will explode more sporadically. • Cinder Cones- build from ejected basaltic lava that begin to harden mid flight (Lutgens et al, 2021). Most fragments being emitted however are only the size of a walnut or pea. Although some will still produce large lava fields which would happen later in the life of these volcanoes. The angle is very steep on these, in fact the steepest angle it can have with the loose material available (Lutgens et al, 2021). Most have cylindrical shapes built in one large eruption, but some are lopped sided depending on the direction of the wind. • Composite Volcanoes- most are located in a narrow zone that rims the Pacific Ocean, “Ring of Fire,” (Lutgens et al, 2021). These are large symmetrical structures consisting of explosively erupted cinders and ash interbedded with lava flows (Lutgens et al, 2021). These have more silica-rich magma which give it a more intermediate composition which can travel less than a few kilometers (Lutgens et al, 2021). These cones are known to have violent large eruptions that will eject pyroclastic material (Lutgens et al, 2021), which also helps the volcano form it’s picture-perfect look in the first place.

H A Z A R D S • A pyroclastic flow would be one of the most dangerous volcanic attacks. This is a mixture of hot gases infused with incandescent ash and large fragments of lava (Lutgens et al, 2021). This can make it difficult to breathe or even suffocate you, as well as impossible to see through while trying to search for safety. Nuee ardentes, would be the “movie-like” flows we are all used to seeing on screen. Translated to “glowing avalanches,” these flows can travel at speeds up to sixty miles per hour. Given the fact that these flows are determined by the gravity which pulls them back towards the earth, these flows can travel for miles before stopping along with the gas. Hikers in Japan were caught in a cloud such as this which claimed the lives of 47 and injured 60 (Lutgens et al, 2021). A great example of the destruction this cloud can cause is the destruction of Pompeii where thousands perished in under a day never to be rediscovered until 17 centuries later (Lutgens et al, 2021).

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E R U P T I O N S T O D AY • An area outside of the united states that would be prone to volcanic eruption is Japan. Japan is home to a mass amount of seismic activity both in the surrounding ocean and the island itself. This we know from history along with the massive tsunamis Japan has seen caused by the quakes. This also results in the formation of volcanos, but also that these volcanoes are relatively active due to this area. • Within the united states, but not the continental united states, we see the islands of Hawaii. These were made primary by what could be determined as shield- volcanoes. The flow of lava overtime was able to form these islands using many different points. Given the history with Hawaii and the 50 eruptions and currently four active volcanoes, to see another eruption would not be unprecedented (Active Volcanoes, (n.d.)). • The hazards for an island like Hawaii would be that, like Pompeii, there would be limited areas to escape to. Depending on the area of the islands you reside, it could be possible to escape the flow of lava, but running from the gas that travels at almost 100 miles per hour, would leave no room for thinking and could corner you somewhere you cannot escape. In terms of Japan, this is a different scenario being over ten times the size of Hawaii. However, Japan is home to one of the largest cities, and although that city is not threatened by the direct threat of lava seeping into their streets, the mass panic caused by a loomed cloud of death can be troublesome for the intensity of population density that occurs within Japan.

R E F E R E N C E S • Communications and Publishing. (2021, July 1). Earthquake intensity scale . Earthquake Intensity Scale U.S. Geological Survey. https://www.usgs.gov/media/images/earthquake-intensity-scale • Active volcanoes of hawaii. Active Volcanoes of Hawaii | U.S. Geological Survey. (n.d.). https://www.usgs.gov/observatories/hvo/active-volcanoes-hawaii#:~:text=The%20Island%20of%20Hawai %27i,only%20about%204%2C000%20years%20ago. • Earthquake danger zone map. (n.d.). https://www.mapsnworld.com/earthquake-danger-zone-map.html • Lutgens, F. K., Tarbuck, E. J., & Tasa, D. (2021). Foundations of Earth Science. Pearson. • Latest earthquakes. (n.d.). https://earthquake.usgs.gov/earthquakes/map/?extent=76.96033%2C-48.33984 • Anss heliplots. U.S. Geological Survey. (n.d.). https://earthquake.usgs.gov/monitoring/operations/heliplot.php?virtual_network=ANSS • Maine Emergency Management Agency. (2020). Earthquake Facts. Maine.gov. Retrieved February 11, 2024, from https://www.maine.gov/mema/hazards/natural-hazards/earthquake/facts#:~:text=Ground%20vibrations%20 during%20an%20earthquake,caused%20by%20the%20ground%20shaking . • Vergano, D. (2021, May 3). What caused the California earthquake? faults explained. Science. https://www.nationalgeographic.com/science/article/140310-earthquakes-usgs-california-faults-science • YouTube. (2012, November 12). Geography lesson: What is a volcano? | twig. YouTube. https://www.youtube.com/watch?v=WgktM2luLok • *Volcano is power-point provided stock photo for slide 10

Module 5

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