Earthquake Science and Engineering

Ömer Aydan

• Publisher: CRC Press
• Year: 2022
• ISBN:
  9781000601602
• Edition: 1
• Topic: Tecnologia e ingegneria
• Subtopic: Ingegneria civile

Earthquakes form one of the categories of natural disasters that sometimes result in huge loss of human life as well as destruction of (infra)structures, as experienced during recent great earthquakes. This book addresses scientific and engineering aspects of earthquakes, which are generally taught and published separately. This book intends to fill the gap between these two fields associated with earthquakes and help seismologists and earthquake engineers better communicate with and understand each other. This will foster the development of new techniques for dealing with various aspects of earthquakes and earthquake-associated issues, to safeguard the security and welfare of societies worldwide.

Because this work covers both scientific and engineering aspects in a unified way, it offers a complete overview of earthquakes, their mechanics, their effects on (infra)structures and secondary associated events. As such, this book is aimed at engineering professionals with an earth sciences background (geology, seismology, geophysics) or those with an engineering background (civil, architecture, mining, geological engineering) or with both, and it can also serve as a reference work for academics and (under)graduate students.

Chapter 1 Introduction

DOI: 10.1201/9781003164371-1

Earthquakes are well known as the natural disasters resulting in huge loss of human lives as well as of properties as experienced in the recent great earthquakes such as the 1999 Kocaeli, Düzce, Chi-chi; the 1995 Kobe earthquakes; the 2004, 2005, 2007 and 2009 off-Sumatra earthquakes; the 2008 Wenchuan earthquake; and the 2011 Great East Japan Earthquake. It is well known that ground motion characteristics, deformation and surface breaks of earthquakes depend upon the causative faults. While many large earthquakes occur along the subduction zones, which are far from the land, and their effects appear as severe ground shaking, the large in-land earthquakes may occur just beneath or nearby urban and industrial zones as observed in the recent great earthquakes. Earthquakes are due to the temporary instability of Earth’s crust resulting from stress state changes. While the accumulation of stress takes for very long period from seconds to thousands of years, which is called stick phase, stress release occurs within a few seconds to 500–600 seconds and it is called the slip phase.

The location, magnitude, occurrence time, the mechanism of earthquakes and the possibility of tsunami are determined by national and international seismological centres, while strong motions are recorded by strong-motion networks in each country and publicized in social networks, TVs and radios. In other words, the earthquakes and related effects are a part of the daily lives of humankind. Earthquakes and related events will continue to occur as long as Earth continues its motion around the Sun in the solar system. Humankind should take counter-measures and design structures against earthquakes and resulting tsunamis for their safe living against their devastating effects.

Most books are intended for either scientific or engineering aspects, and there is no book addressing both aspects. This book addresses scientific and engineering aspects of earthquakes, which are generally taught separately. This book intends to fill the gap between these two fields associated with earthquakes and to make seismologists and earthquake engineers understand and communicate with each other for developing new techniques to deal with various aspects of earthquakes and earthquake-induced issues for better and safe societies worldwide.

This book specifically attempts to provide

• A unified treatise of scientific and engineering aspects of earthquakes
• Clear definitions and explanation of fundamental concepts
• Explanation of procedures for determining the fundamental parameters essential to the science and engineering of earthquakes. Specifically, location, magnitude, wave propagation, focal mechanism related to scientific aspects and analyses of strong motions, measurements, their utilization in earthquake-proof design, tsunami-resistant structures, the design of structures against permanent ground movements, etc.
• In-depth view of procedures and solution techniques

Therefore, this book is expected to address readers having an earth-science background (geology, seismology, geophysics), an engineering background (civil, architecture, mining, geological engineering) or both, and simultaneously it can be a reference book for undergraduate and graduate students.

Chapter 2 is concerned with the physics of earthquakes and explains the background of earthquakes starting from laboratory experiments to real-world occurrences. Laboratory experiments involve fracturing of intact rock, slippage of artificial and natural discontinuities. These experiments explain various physical variations such as wave velocity, electrical resistivity and acoustic emission (AE) activities before and during fracturing. Furthermore, acceleration responses of mobile and stationary sides are presented and discussed in relation to strong-motion observations. Finally, some observations of the differences between earthquakes and volcanic eruptions are explained and discussed.

Earthquakes are always associated with motions that propagate as waves. Chapter 3 presents the fundamental law of equation of motion, which establishes the equations of wave propagation. The wave propagation induced by earthquakes is also utilized to infer the interior structure of Earth as well as the hypocenter data and magnitude of earthquakes.

Faults and faulting mechanisms are the most important elements in the science and engineering of earthquakes. Faults are known to be geological discontinuities, and their temporary instability resulting in slippage causes disastrous effects on structures, environment, and life. The accumulation of stress causes their instability, and evaluation of the critical conditions is essential. In Chapter 4, the stress state in the close vicinity of various types of faults, the asperities and their stress states during stable and unstable conditions are explained through actual experiments. For this purpose, results of some photoelasticity experiments, which enable us to see the stress state visually, are presented for some typical faulting conditions and the same conditions are also analysed through the finite element method. Some empirical procedures are described to evaluate some interrelations for estimating potential earthquakes from fault length and relative slip amount. In the final part, procedures for inferring focal mechanisms from waves and fault striations are explained.

Every earthquake causes vibrations and temporary and/or permanent movement of ground. The ground motions caused by earthquakes in/around their epicentral area having a dominant frequency >1 Hz would be categorized strong ground motions. These ground motions recorded as acceleration and/or velocity decrease in amplitude in relation to the distance, while the motions recorded as displacements having dominant frequency <1 Hz are called broad-band ground motions, which are commonly used to infer the hypocenter and magnitude of earthquakes. Chapter 5 describes ground motions and their characteristics, and techniques for measuring and recording them. As it is difficult to measure ground motions at every location, empirical, semi-analytical or numerical procedures are described to estimate ground motions. In addition, this chapter also explains some procedures developed to infer the strong ground motion parameters from the collapse, failure or slippage of simple structures and simplified reinforced concrete structures. These methods are also of great importance to assess the magnitudes of past earthquakes as well as modern earthquakes where instrumental data is scarce.

Chapter 6 is concerned with response analyses of structures, which is of great importance in the evaluation of behaviour of structures under earthquake motions. First, the fundamental procedures for response analyses are described and the fundamental concepts for the vibration of structures are explained utilizing some simplified analyses. Then the techniques used for measuring and analysing the vibrational characteristics of structures such as Fourier spectra and response spectra methods are presented. Some specific examples of vibration measurements for model structures as well as actual structures are given. Furthermore, some empirical procedures for estimating the natural frequencies of some structures are presented and compared with actual data. In addition, the response and vibrational characteristics of large structures such as dams, tanks, wind turbines, underground openings, caverns and shafts are explained.

The effects of past earthquakes and associated surface ruptures on engineering structures should be well understood for their earthquake-proof or earthquake-resistance design and performance. Chapter 7 explains the observed effects of past earthquakes and associated surface ruptures on various engineering structures such as bridges and viaducts, dams, tunnels, failures of slopes and rockfalls, embankments and foundations and deformation of underground caverns and shafts. Ground liquefaction is also an important geotechnical phenomenon. The mechanism and estimation of ground liquefaction and associated lateral spreading and their effects on various structures are explained.

Chapter 8 is concerned with the seismic design of various structures. First, the fundamental procedures of seismic design such as seismic coefficient method, modified spectral seismic coefficient method, modal pushover and response analysis methods are described. Then some specific seismic design procedures for dams, bridges and viaducts, tunnels, pipelines, embankments, slopes, foundations of critical structures, buildings, minarets and dome-type structures are explained. As ground liquefaction is also a very critical issue, the techniques for assessing ground liquefaction and its effects such as uplift, settlement and lateral spreading of structures are also presented.

The devastating 2011 Great East Japan Earthquake (GEJE) and the 2004 off-Sumatra (Aceh) mega earthquakes showed the tremendous extent of structural damage tsunamis can cause. In Chapter 9, the mechanism of tsunamis and their effects on various engineering structures are explained through some specific examples the author observed during the reconnaissance of the 2011 GEJE, and the 2004 Aceh mega earthquakes are explained. Laboratory-scale tsunami model tests are also described to illustrate the forces resulting from tsunamis. Then, procedures for evaluating the effects of tsunamis on structures and the principles of tsunami-proof structural design are explained. Finally, an empirical procedure for estimating the magnitude of earthquakes from tsunami boulders is presented, and some specific examples are given.

Earthquake prediction, which requires the prediction of the time of occurrence, magnitude and location, is always the most desirable yet most difficult issue in earthquake science. Chapter 10 is concerned with this issue. First, the physical background on anomalous phenomena observed in earthquakes is presented, and the implications of responses of rocks and discontinuities during fracturing and slippage are discussed. Then, the available methods of earthquake prediction are described together with some attempts of prediction. In recent years, the GPS method has become widely used. A section is dedicated to earthquake prediction using the GPS method, and it is shown that prediction of the location and time of earthquakes may be possible. Furthermore, the possibility for estimating the magnitude is discussed. Several specific examples of anomalous phenomena during earthquakes in Turkey are given, and the application of the multi-parameter monitoring system for earthquake prediction in Denizli Basin of Turkey is described. In the final part, some principles of earthquake prediction using various techniques are established.

Chapter 2 Physics of earthquakes

DOI: 10.1201/9781003164371-2

2.1 Causes of earthquakes

The main cause of earthquakes are changes in stresses of the Earth’s crust and its temporary mechanical instability. The plate tectonic theory based on Wegener’s theory on continental drift proposed in 1912 is often used to explain the occurrence of quakes on the Earth, called “earthquakes.” However, Wegener’s theory was not well received among mainstream geologists and geophysicians until the discovery of palaeomagnetism and modern seismology. Figure 2.1 shows the plots of earthquake epicentres and major plates of the Earth.

Figure 2.1 (a) World seismicity and (b) the major plates of the Earth. (Modified from Udias (1999).)

It is often assumed that seismic regions coincide with plate boundaries. There are three major plate boundaries, namely, convergent, divergent and transform plate boundaries. High mountains are found at/along convergent boundaries and plate thickness increases up to 70 km. Furthermore, large earthquakes occur along convergent plate boundaries, while the magnitude of earthquake along divergent plate boundaries is generally smaller. Transform plate boundaries may have a dextral or sinistral sense of relative slip, and the magnitude of earthquakes generally ranges between those of earthquakes caused by convergent and divergent plate boundaries (Figure 2.2).

Figure 2.2 Types of plate boundaries.

The driving force of plates is often said to be due to ma...