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Numerical Integration Methods and Seismic Response Spectra for Single- and Multi-Component Seismic Input
Published in Franklin Y. Cheng, Matrix Analysis of Structural Dynamics, 2017
An earthquake is an oscillatory, sometimes violent movement of the earth’s surface that follows a release of energy in the earth’s crust. This energy can be generated by sudden dislocation of segments in the crust, volcanic eruption, or man-made explosion. Most destructive earthquakes, however, are caused by dislocation of the crust. When subjected to geologic forces from plate tectonics, the crust strains, and the rock in the crust is stressed and stores strain energy. When stress exceeds the rock’s ultimate strength, the rock breaks and quickly moves into new positions. In the process of breaking, strain energy is released and seismic waves are generated. These waves travel from the source of the earthquake, known as the hypocenter or focus, to the surface and underground. The epicenter is the point on the earth’s surface directly above the hypocenter, as shown in Fig. 7.1. An earthquake’s location is commonly described by the geographic position of its epicenter and its focal depth. The focal depth of an earthquake is the distance from epicenter to focus. These terms are illustrated in Fig. 7.1.
Introduction
Published in Hector Estrada, Luke S. Lee, Introduction to Earthquake Engineering, 2017
Although the precise force mechanisms causing movement of the lithospheric plates continue to be debated, there is substantial agreement that heat from the earth’s core serves as the primary source of energy for these forces. Also, the general outlines of the major plates have almost conclusively been established. In fact, this outline is clearly illustrated when the location of the epicenters of recent earthquakes is plotted on a global map as shown in Figure 1.12. At the boundaries of the plates, rocks fracture, usually at many locations, creating a web of smaller plates with edges that rub and push relative to each other; these edges are called faults. On average, these faults have the potential to displace approximately 2 inches per year. When the rubbing and pushing is prevented, elastic energy accumulates along the edges of the plates. When this energy is released with a sudden movement (slip), it causes brief strong ground vibrations. The specific location (generally a volume of rock) where the movement or energy release occurs is known as the focus, or hypocenter. The point on the earth’s surface directly above the hypocenter is called the epicenter. Usually, the vibrations cause the rocks near the focus to become unstable; and as these rocks settle into a new equilibrium state they cause aftershocks. The discipline that studies seismic activity is known as seismology, and will be discussed further in Chapter 2.
Introduction
Published in Sreevalsa Kolathayar, T.G. Sitharam, Earthquake Hazard Assessment, 2018
Sreevalsa Kolathayar, T.G. Sitharam
An earthquake is a sudden vibration of the earth caused by an immediate release of energy during rupture of rock that creates seismic waves. The place within the earth’s crust where an earthquake originates is called the hypocenter, or focus, of the earthquake (Fig. 1.1). The point vertically above this, on the surface of the earth, is known as the earthquake’s epicenter.
Seismic activity recorded by a single OBS/H near the active Longqi hydrothermal vent at the ultraslow spreading Southwest Indian Ridge (49°39′ E)
Published in Marine Georesources & Geotechnology, 2019
Yunlong Liu, Chunhui Tao, Cai Liu, Lei Qiu, Vera Schlindwein, Haijiang Zhang, You Tian, Hanchuang Wang
Determining the hypocenter location requires knowledge of P- and S-wave velocity structure. We calculated an average 1D P-velocity model near our OBS/H from the three-dimensional seismic tomography of Zhao et al. (2013). S-wave velocity model was inferred from P velocities using an empirical relationship from Brocher (2005). The one-dimensional velocity model of P and S is shown in Figure 5. After that, we pick P arrival times manually from hydrophone component and S arrival times from horizontal component with 0.05 and 0.15 s uncertainty, respectively. And the travel time difference Ts–Tp of most events ranges from 0.25 to 3 s with the average difference error of 0.1 s.