Case Study Boelsche – Valdivia Earthquake 1960

May 22, 1960 marks the date of the most powerful earthquake ever recorded, in terms of the moment magnitude scale. This case study will investigate the causes behind the seismic event, the geography of it and the secondary effects that resulted.

In order to engage with the nature of seismology, the reader must have a clear understand of what a subduction zone constitutes. In an article for Live Science magazine, Becky Oskin says that a “subduction zone is the biggest crash scene on Earth” that takes place over millions of years (Oskin, 2015). When the much denser oceanic plate pushes against the less dense continental one, subduction forces the oceanic plate to bend underneath the other, causing the formation of volcanoes, tsunamis and the earth’s largest earthquakes. Figure 1 illustrates the subduction zone created by the oceanic Nazca plate’s collision into the South American continental plate.[1] The Pacific Ocean’s “Ring of Fire” outlines a massive series of subduction zones that are responsible for a large percentage of the earth’s most dangerous seismic events today, as depicted in Figure 2. [2] Oskin compares the subducting collision of two tectonic plates to rubbing sandpaper together, in that “the crust sticks in some places, storing up energy that is released in earthquakes” (Oskin, 2015). Since subduction zones create the largest faults in the world, they directly correlate with the most dramatically powerful earthquakes. Along the Peru-Chile trench, created by the subduction of the Nazca plate under the South American one, is one of the world’s largest and most active faults.

                                                                                

According to the U.S. Geological Survey, at 10:02 UTC (around in the morning local time) lasted for 35 seconds but it would devastated one-third of the buildings in Concepción, reaching 8.1 on the moment magnitude scale (USGS, 2016). This initial earthquake would kill 150 people, according to an article published immediately following the event by William E. Rudolph, and it marked the beginning of “ten days of terror” that would ultimately leave 1000 dead and 350,000 homeless (Rudolph, 1960). The second quake would occur slightly over 24 hours later, at 10:30 UTC in the Nahuelbuta National Park, just south of Concepción, reaching 7.1 mw  (USGS, 2016). The third would come the next day at 18:56 UTC in the same area, totaling 7.8 mw (USGS, 2016). As powerful and destructive that the three Concepción earthquakes were, they would come to alert the rest of the population for what would come.

Roughly 15 minutes after the 7.8 mw earthquake south of Concepción, at 15:11 local time, the town of Valdivia would endure 11 uninterrupted minutes of seismic shaking (Seismo Blog, 2015).  USGS shows the epicenter of the 9.5 mw earthquake situated on the coast just east of Lleulleu Lake, which was actually several hundred kilometers directly north of Valdivia, which appears in Figure 3 (USGS, 2016). Using the previous system, the Richter scale, the [3]moment actually only measured 8.3, which is how older sources refer to the event; but the moment magnitude scale that the geophysics community adopted in the 1970s converted the moment into the 9.5 mw by which we refer to it today (USGS, 2003). This is not the most powerful earthquake to have ever taken place, but it is the highest ranking earthquake to be recorded due to the recent advancements and global distribution of seismic and geological measuring instruments by both the United States and the Soviet Union.

The immense toll in fatalties and damages was largely due to the secondary effects of the Valdivia earthquake that took place throughout the following days after May 22, inlcuding tsunamies, flooding, lahars, and the even eruption of the Cordón Caulle volcano. Related to the tsumani and the destruction of at least 40% of all structures in the area, flooding ran rampent for several days following May 22. Figure 4[4] is a still from flooding in Quellon, a costal island community several hundred kilometers south of Valdivia. The worst mass wasting came to be known as the Riñihuazo flood. When several lahars resulted from the Valdivia earthquake, the Riñihue Lake become completely blocked from a connected outflow river, the San Pedro (Diario Austral, 2010). This cause the lake to rise at an alarming rate and pour into the adjacent communities. Then, on May 24, the Puyehue-Cordón Caulle Volcano, some 200 kilometers from the epicenter of the earthquake, would erupt (Rudolph, 1960). The eruption initiated itself with a powerful explosive phase, creating a clumn of ash 8 kilometers high from the source. The volcano would not erupt again for another 51 years.

The populations of Chile have been adapted to seismic activity for centuries, since the faults lining the Peru-Chile trench are among the most active in the world. Especially due to somewhat large earthquakes in the 1920s and 1930s, Chilean society still had earthquakes fresh in its mind (Diario Austral, 2010). Citizens were extremely fast in evacuating the buildings, and were able to band together very quickly. Most of the problems were structural, since Chile at the time was not nearly as economically affluent as it is today. However, the seismic event was literally felt throughout the world, and many nations quickly began to pour in aid to stimulate the initial recoveries (Diario Austral, 2010). Mexico especially sent large amounts of financial aid and donated several schools to the Valdivia area. The following video recalls the devastating chain of events and offers telling footage of the time:

 

Sources of images:

[1] Figure 1: “Eruption on Volcán El Reventador,” Science Thoughts, retrieved April 22 2017 from http://sciencythoughts.blogspot.com/2012/11/eruption-on-volcan-el-reventador.html

[2] Figure 2: “Ring of Fire,” National Geographic, retrieved April 21 2017 from https://www.nationalgeographic.org/encyclopedia/ring-fire/

[3] Figure 3: USGS, Last modified 2016. M 9.5 – Bio-Bio, Chile; retrieved April 28 2017 from https://earthquake.usgs.gov/earthquakes/eventpage/official19600522191120_30#map

[4] Figure 4: “Terremoto de Valdivia 1960,” Volcanes históricos; retrieved April 28 2017 from http://www.volcaneshistoricos.com/terremoto-de-valdivia-1960/

Look out southern Midwest!

https://weather.com/storms/tornado/news/severe-weather-tornado-forecast-late-april-2017

Look out southern Midwest!

The past couple weeks have been very stormy in the East Coast, Gulf Coast, and Midwestern regions of the US. Severe thunderstorms are expected to pass through eastern Texas, Arkansas, Missouri, Tennessee and Kentucky and up into Indiana and Illinois. These storms could bring huge, damaging chunks of hail, and as much as 7 inches of rainfall in some areas. Forecasters are warning residents in these regions to watch for flashfloods. There is also talk of potential tornado formations, giving sections of Tornado Alley the chance to live up to its name.

Tornadoes rely on severe differences in air mass temperatures to form. The succession of specific air conditions during a severe thunderstorms makes the formation of tornadoes and ground contact generally unlikely, but the risk associated with them is so great that potential warnings in advance are the duty of forecasters. Although the path of a tornado once it actually does make contact is wildly unpredictable, the conditions leading to the tornado itself are very easy to identify, thus issuing tornado watches and warnings are not hard to do.

Storm Moves into Mississippi

http://djournal.com/news/severe-weather-takes-aim-mississippi-southern-states/

Forecasters are claiming an area including the cities of Jackson, Tupelo and Vicksburg which houses more than 1.3 million people is at risk, in response to the national Storm Prediction Center’s placing a large part of Mississippi at the highest risk of severe storms on Saturday.

The storm is expected to leave the Mississippi area by the evening. Forecasters say parts of the Louisiana, Alabama and Georgia could also see storms Saturday and Sunday.

Thunderstorms are becoming more and more common in the east coast due to the coming of the hot, humid summer months. The gulf region states are particularly humid all year round and have a tendency to experience intense, but generally quick, thunderstorms during the hottest months.

Landslide in Alcañiz

http://www.20minutos.es/noticia/3014368/0/desprendimiento-casas-alcaniz-teruel/

An intense landslide on the hill of Pui Pinos of the city of Alcañiz took place on April 17, and shifted at least five buildings of the Round of Teruel of this town, which has caused the eviction of 33 people. Although no deaths have been reported, millions of dollars worth of property damage have resulted.

Alcañiz is a town and municipality of Teruel province in the autonomous community of Aragon, Spain. The town is located on the banks of the river Guadalope. The area is filled with huge castle structures which put lots of pressure on the slopes in the area.

The evicted neighbors have been transferred to the Hotel Guadalope. Of the 33 people evicted, 12 of them lived in houses that have collapsed and were located on a hillside, in the Round of Teruel, in the old passage of the N-232. The mayor of Alcañiz, Juan Carlos Gracia Suso, has visited the people who are in the Hotel Guadalope, where their accommodation has been arranged.

Spanish word for landslide: corrimiento de tierras

Earthquake in Navarra, Spain

http://politica.elpais.com/politica/2017/03/10/actualidad/1489129708_796669.html

This article is in Spanish, but you can easily translate it by plugging it into Google translate. Most of the facts will be obvious to an English-speaking reader without relying on outside resources, however. (Sorry, I’m a Spanish major so “El País” is a news source I use a lot!)

On March 10th of this year, a 4.4 scale earthquake hit the Autonomous Community of Navarra in Northern Spain (in the Pyrenees, bordering France). The best-known city in this area is Pamplona, where they host the famous Running of the Bulls. According to the article, there was some property damage; several people reported broken windows and other household objects. Luckily, there were no fatalities reported, and apparently no injuries. I imagine the experience was somewhat like our experience in the late-summer of 2011: extremely surprising, and disruptive in many cases to be sure, but not at all detrimental. Scary, shocking, but not devastating. I’m sure the bulls will be running just fine come summer!

Fun vocab word of the day: terremoto = earthquake. Make sure you roll the R sound!

Lightning in Pensacola, FL

https://weather.com/storms/severe/video/lightning-strike-hits-in-pensacola-fla

I wanted to share this because my little sister recently moved to Pensacola for flight training, and I always worry for her! She’s a strong and capable person, but she’s so far away and I can’t help but think about her wellbeing.

On January 2 of this year, an extremely intense bolt of lightning struck the road right in front of a driver, who recorded the incident on this phone. As you can see in the brief video, the strike had the potential of causing very serious harm to anyone or anything in its path. Luckily, no one was hurt by this bolt in particular.

As we have discussed several times in class, Florida is subject to frequent tropical storms, especially during the hurricane season months. These months generally include Spring through mid-Fall; January does not fall into this category of “hurricane season months,” or what we in Virginia would except to be thunderstorm season. So why was there such a hazardous lightning bolt making contact in Pensacola in the off-season?

http://www.wjhg.com/content/news/Storms-strong-winds-damage-homes-and-school-in-Pensacola-409319755.html

This article documents a particularly strong wind storm that had gone through Pensacola the previous day. I could surmise that the lightning bolt was connected to this event. Strong wind storms like this one are by no means restricted to a defined seasonality. Of course, we can talk about the likelihood of a storm’s occurrence falling into a certain time frame, that being when the air and surrounding water sources are warmer and more likely to create low pressure systems with lifting, stable, wet air. But in reality, serious storms can occur at any point in the year, especially in areas like Pensacola, where the air is generally humid and warm all year long. According to this article an elementary school was damaged, but no injuries were reported. This incident provokes certain questions of mitigation and social response: no one was hurt, which implies some kind of evasive action (although the article doesn’t specify that any were taken), yet the school was damaged, begging the question of why it hadn’t been built to be more sturdy? An elementary school is a public structure where the entire community has an intimate investment, and an area like Pensacola should already be well-accustomed to severe wind storms.