Plate Tectonics SLO

Plate Tectonics - Geology 101

The History of the World's Most Violent Plate Boundaries

Convergent Plates Boundaries and a History of their Most Violent Earthquakes

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Introduction

Convergent Plate Boundaries are formed when two tectonic plates collide with one another and begin to push against each other. These boundaries are where the earth’s mountain ranges are formed as the two plates grind against each other and build upward. These plate boundaries come in two common forms oceanic-continental and continental-continental.

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The former involves an oceanic plate sliding or subducting beneath a continental plate and causing the continental plate to rise atop of it. These zones are also what gives rise to many of the on land volcanoes across the world. In addition a trench is formed along the subduction zone creating some of the deepest places on earth. Finally these zones create extremely powerful earthquakes and tsunamis

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The latter involves two continental plates slamming into each other and building a mountain chain up along the convergent plate boundary. These areas are great for building tall mountain ranges as the continental crust doesn’t like to sink or subduct so they will simply push each other higher and higher. Finally these boundaries cause the continental crust to crumble so instead of lots of stress and buildup along the boundary the rock crumbles and is pushed upward lowering the risk of large earthquakes.

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Nazca Plate

The Nazca Plate, best known for massive earthquakes and equally massive subduction zone stretching some 7500km along the west coast of south america. The Nazca plate was once part of the larger Farallon plate which split off nearly 23 Mya and prior had begun building the andes mountain range 140 Mya. As mentioned before Nazca has created some rather massive earthquakes including the May 22, 1960 earthquake near Valdivia which was a magnitude 9.5 and the February 27, 2010 earthquake in the Maule Region of Chile which was a magnitude 8.8, the former of which holds the record as the largest earthquake ever recorded followed closely by the  28 March 1964 earthquake Prince William Sound, Alaska which was a magnitude 9.2. The 9.5 would not only create a tsunami that would sweep across the west coast of the US and Hawaii but also cause a month-long volcanic eruption in Chile along with causing the deaths of 1,655 people and 4.8 billion USD in damages across a rupture zone spanning 500km. The smaller 8.8 would cause the deaths of 521 people and 30 billion USD in damages across a rupture zone of 431km separated into two sections: a 118km heading south and a 313km rupture zone heading north.  

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Runner ups

1: As mentioned before the 9.2 earthquake in Alaska is the current runner up to the record holding 9.5 in chile. This earthquake would see the Prince William Sound region devastated by both the second largest recorded earthquake but also two types of tsunami, 1 tectonic (the larger variant) and 20 local tsunami’s (the smaller variant) these would go on to cause both more property damage and 122 deaths from all across the pacific. The Earthquake also caused over 750 million USD in damages in Alaska. 

2: A more recent earthquake in Sumatra, Indonesia December 26, 2004 saw a magnitude 9.1 caused by the subduction zone along the eastern Indian plate and western Burma plate. The earthquake would generate a 50-100ft high tsunami, devastated the east indies, caused 14 billion USD in damages and killed 227,898 people making it one of the deadliest natural disasters in history. The earthquake would also trigger remote earthquakes on plate boundaries as far away as southern Alaska and cause a 10mm vibration across the planet, basically a motion from the middle to the end of the tip of you pinky finger. 

(seen here is a map of the local aftershocks)

3: A more infamous and even more recent earthquake originating from the Japan trench, the Tōhoku, Japan March 11 2011 earthquake which would see the middle island of japan, Honshu devastated by both a magnitude 9.0 earthquake and a 20-26 foot high tsunami stretching 180km wide. The event saw the deaths of 19,747 people, generated over 13 thousand aftershocks (over 80 of those in japan were magnitude 6.0-7.0 and 896 have been at or over 5.0) and 360 billion USD in damages making it the most costly natural disaster to date. The earthquake was Japan’s san andreas, they knew it was coming since the Kanto quake in 1923, started looking for its arrival in 1969, they prepared for it and had been tracking the plate movements and waiting since 1976 and yet when it finally came in 2011 (nearly 40 years later and 90 years after the Kanto quake) it arrived over 300km north of the area they had been readying to receive the earthquake and devastated the northern half of the main island.

(these aftershocks are just from March 11th to March 14th)

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Conclusion

These more famous and massive earthquakes have been devastating but many more occur every year at subduction zones around the world producing billions of dollars in damages and making the regions surrounding them dangerous. While we may love to build our homes near the towering mountains casually built by these convergent plate boundaries over millions of years they can just as easily level our metal mountains in but a few seconds. 

Note many of the worlds largest and most heavily populated cities lie near or atop these subduction zones