Plate Boundaries and Natural Hazards

Joao C. Duarte, Wouter P. Schellart

• Publisher: American Geophysical Union
• Year: 2016
• ISBN:
  9781119054214
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Geology & Earth Sciences

The beginning of the new millennium has been particularly devastating in terms of natural disasters associated with tectonic plate boundaries, such as earthquakes in Sumatra, Chile, Japan, Tahiti, and Nepal; the Indian Ocean and the Pacific Ocean tsunamis; and volcanoes in Indonesia, Chile, Iceland that have produced large quantities of ash causing major disruption to aviation. In total, half a million people were killed by such natural disasters.These recurring events have increased our awareness of the destructive power of natural hazards and the major risks associated with them. While we have come a long way in the search for understanding such natural phenomena, and although our knowledge of Earth dynamics and plate tectonics has improved enormously, there are still fundamental uncertainties in our understanding of natural hazards. Increased understanding is crucial to improve our capacity for hazard prediction and mitigation.

Volume highlights include:

• Main concepts associated with tectonic plate boundaries
• Novel studies on boundary-related natural hazards
• Fundamental concepts that improve hazard prediction and mitigation

Plate Boundaries and Natural Hazards will be a valuable resource for scientists and students in the fields of geophysics, geochemistry, plate tectonics, natural hazards, and climate science.

Read an interview with the editors to find out more:
https://eos.org/editors-vox/plate-boundaries-and-natural-hazards

1
Introduction to Plate Boundaries and Natural Hazards

João C. Duarte^1,2 and Wouter P. Schellart^2,3

¹Instituto Dom Luiz and Departamento de Geologia, Faculdade de Ciências, Universidade de Lisboa, Lisbon, Portugal

²School of Earth, Atmosphere and Environment, Monash University, Melbourne, Victoria, Australia

³Faculty of Earth and Life Sciences, Vrije Universiteit Amsterdam, Amsterdam, Netherlands

ABSTRACT

A great variety of natural hazards occur on Earth, including earthquakes, volcanic eruptions, tsunamis, landslides, floods, fires, tornadoes, hurricanes, and avalanches. The most destructive of these hazards, earthquakes, tsunamis, and volcanic eruptions, are mostly associated with tectonic plate boundaries. Their occurrence has stimulated scientists to think about their spatial and temporal distribution, and their physical causes, within the atmosphere, in the oceans, or deep within the Earth's interior. It is no coincidence that two of the greatest earthquakes ever recorded occurred at the start of the decade in which the theory of plate tectonics, the grand unifying theory of the solid Earth sciences, was developed. In this chapter, we introduce the different natural hazards associated with plate boundaries, including a discussion of one of the greatest natural disasters in history, the 1755 great Lisbon earthquake that stimulated research into the internal workings of our planet and the development of seismology.

1.1. THE AFTERMATH OF THE 1755 GREAT LISBON EARTHQUAKE

The 1755 great Lisbon earthquake was one of the most powerful seismic events ever documented. With an estimated magnitude (M_w) of 8.5 to 9, it shocked Lisbon on the morning of All Saints Day while many residents were in churches [Martinez‐Solares and Arroyo, 2004; Gutscher et al., 2006; Oliveira, 2008 and references therein]. Forty minutes after the main shock, three giant waves came up the Tagus River, flooding the harbor and the downtown area [Baptista et al., 1998; 2003]. The tsunami destroyed several buildings along the west coast of the United Kingdom and spread across the Atlantic pounding the east coast of the Americas [Lyell, 1830; Batista et al., 2003]. Casualty estimates from the ground shaking, the tsunami, and the resulting fires ranged from 60,000 to 100,000 people, leaving Portugal devastated [Pereira, 2006; Oliveira, 2008]. The visionary Portuguese minister Marquês de Pombal immediately ordered a survey with 13 questions to be sent around the country. Today, this survey allows us to understand much of what happened that day [Oliveira, 2008].

Some of the questions were amazingly prescient for 1755 and opened the door to modern seismology. Among these were: “At what time did the earthquake begin and how long did the earthquake last? Did you perceive the shock to be greater from one direction than another? Number of houses ruined in each parish; Were there any special buildings and what is their state now? Did the tide get low or high first; How much did it grow more than normal …?” [Oliveira, 2008]. Even though the main objective of the survey was to understand the magnitude of the damage, it is clear from the questions that the Marquês also aimed to understand the characteristics of the event. Similar queries were made by king Fernando VI of Spain [Martinez‐Solares, 2000; Oliveira, 2008].

Today it is possible to construct maps of the intensity of ground shaking from the surveys, and place the source approximately 200 km southwest off the Cape Saint Vincent, the southwest corner of the Iberian Peninsula, and somewhere along the diffuse Azores‐Gibraltar plate boundary zone [Martinez‐Solares et al., 1979; Oliveira, 2008 and references therein]. Nonetheless, the specific structure that generated the quake is still debated [Zitellini et al., 2001; Gutscher et al., 2006; Rosas et al., this volume].

The great Lisbon earthquake was significant not only for its enormous societal impact. As mentioned above, the 1755 event was also essential to the development of modern seismology and in many ways it changed the way people saw the world [Lyell, 1830]. The 1755 event attracted the widespread attention of the main thinkers of the then current epoch of enlightenment. Philosophers such as Voltaire, Rousseau, Kant, and many others realized that, contrary to what was previously thought, earthquakes were not a punishment from God [Zitellini et al., 2009]. Instead, they suspected, earthquakes and tsunamis had natural causes! Immanuel Kant wrote three essays in 1756 in which he developed a theory of the causes of earthquakes and gets close to recognizing some of the main characteristics of plate boundaries, more than 200 years before the theory was born [Kant, 2012]. The rationalization that the “firm ground” could actually move in such a tremendous way enlightened the minds of many thinkers of the time and contributed to shaking the widely held belief in a solid, immobile, unchanging Earth.

Immanuel Kant clairvoyantly argued that earthquakes are caused by sudden ground movements triggered by the abrupt displacement of gases in the interior of “interconnected” caverns: “The first thing to be observed is that the ground under us is hollow and its caverns extend very widely, almost in a single interconnected system, even under the floor of the sea” [Kant, 1756a]. Inspired by Athanasius Kircher’s Mundus Subterraneus [1664], he suggests that earthquakes occur along a network of “caverns” and “vaults” [Kant, 1756b]. This was in part a result of the recognition that there were other earthquakes in Iceland the same day the 1755 earthquake struck: “the continued effect [felt] simultaneously in widely separated places, including Iceland and Lisbon, which are separated by more than a half hundred German miles of sea and were set in motion on [the] same day, deliver irrefutable testimony, all these phenomena confirming the interconnections of these subterranean caverns”[Kant, 1756a]. It is also fascinating to note that Kant associated these “veins” with topography: “one thing is certain, namely that the direction of the caverns is to the mountain ranges…. For these occupy the lowest parts of long valleys bounded sides by parallel mountains…. This is why Peru and Chile are more subject to frequent tremors than any other countries in the world” [Kant, 1756a].

Kant was strongly inspired by Newton’s theory of the physical world and used logical reasoning and experimentation to understand the causes of earthquakes. Based on the work by Nicolas Lemery and some of his experimental knowledge, he ascribed those causes to the “conflagration” of fires (chemical reactions) and “emission of flammable vapors trapped inside subterranean regions…that break out in flames at the orifices of the volcanoes” [Kant, 1756a]. He also recognized that the subsequent tsunami was caused by the “sudden movement of the seafloor” that “set the water in motion.” Already in 426 BC the Greek philosopher Thucydides suggested that tsunamis were associated with earthquakes [Smid, 1970]. Much of this knowledge was forgotten, especially during medieval times, to be later revived during the Renaissance and the Age of Enlightenment. Kant, by investigating the propagation of the tsunami with the arrival times and intensity at certain points of the European shores, calculated the pressure required to put the water in motion and the area of seafloor that was suddenly uplifted [Kant, 1756b]. Although Kant's ideas were far removed from the modern concepts of plate tectonics, he recognized that earthquakes occurred along linear‐like features that move causing tremors and topography. He also noted that some ...

Table of contents

• COVER
• TITLE PAGE
• TABLE OF CONTENTS
• CONTRIBUTORS
• PREFACE
• 1 Introduction to Plate Boundaries and Natural Hazards
• Part I: Reviews
• Part II: Earthquakes and Related Natural Hazards
• Part III: Volcanoes and Related Natural Hazards
• INDEX
• END USER LICENSE AGREEMENT