China
Africa
Explore chapters and articles related to this topic
Earthquake Precursory Studies in India
Published in Ramesh P. Singh, Darius Bartlett, Natural Hazards, 2018
Brijesh K. Bansal, Mithila Verma
The multiparameter data, including seismological, hydrological, hydrogeochemical, GPS-based geodesy and EM emission in ULF bands, have been investigated in search of precursory signals. In recent times, near-real-time monitoring of earthquakes has enabled a short-term scientific forecast based on the phenomenon of the nucleation of smaller earthquakes, as well as foreshocks. The proposed method is based on the premise of detecting and observing a nucleation zone of foreshock cluster, which increases over a time window of 50–100 hours prior to a Mw ~4–5 earthquake. Deepening of such a nucleation zone helps to locate a hypocentre of a future moderate-size earthquake at the base of the seismogenic layer (Gupta et al. 2005). Closely spaced seismic networks set up in the Koyna–Warna region have helped in forecasting some of the recent earthquakes of Mw ≥4 in the Koyna region, on 13 November 2005 (Mw 4.0), 26 December 2005 (Mw 4.2), 17 April 2006 (Mw 4.7), 14 October 2007 (Mw 3.4), 2 July 2008 (Mw 3.0) and 12 December 2009 (Mw 5.1), based on the nucleation process. These successful forecasts have been made since 2005, raising hopes for possible earthquake prediction in the future.
Engineering Seismology Overview
Published in Hector Estrada, Luke S. Lee, Introduction to Earthquake Engineering, 2017
The focal depth is used to classify earthquakes as: shallow for focal depths less than 70 km (43 miles), intermediate for focal depths between 70 km (43 miles) and 300 km (186 miles), and deep for focal depths greater than 300 km (186 miles). Focal depths have been known to be as large as 720 km (450 miles). Shallow earthquakes are more destructive than others because the mass of the rock above deeper earthquakes attenuates their shock waves. Shallow earthquakes generally occur near ocean trenches, like coastal California earthquakes, which have focal depths of less than 16 km (10 miles). Most moderate-to-large shallow earthquakes are preceded by smaller quakes, called foreshocks, and followed by smaller quakes called aftershocks. Foreshocks are precursors of the impending fault rupture, while aftershocks result from adjustments to the stress imbalance in the rocks produced during the rupture.
Seismic ground motion parameters: An overview
Published in Edmund Booth, Seismic Design Practice into the Next Century, 1998
As is generally known, earthquakes of significant size are sometimes preceded by one, or rarely more, foreshocks and most often by a variable number of aftershocks. The very definition of the aftershock concept, however, does not begin to be as clearcut as might be thought at first glance (Mohammadioun, 1992). Aftershocks are viewed by most individuals as being events with relatively insignificant magnitudes. This is a misconception (as has once again been demonstrated with the series of events that has occurred in the Appenines, central Italy, in September and October 1997), for many aftershock sequences contain events as strong or nearly as strong (more rarely stronger) than the main, or inital, event. In such instances, the term swarm is often applied, but actually there is a continuum between the seemingly random pattern of events that constitute these and the more “orderly” structure of classical aftershock sequences. Furthermore, if the main shock has a magnitude of 6 or more, chances are that it is actually a multiple event composed of two or more shocks in rapid succession.
Mitigation of earthquake-induced damage of breakwater by geogrid-reinforced foundation
Published in Marine Georesources & Geotechnology, 2018
Babloo Chaudhary, Hemanta Hazarika, Akira Murakami, Kazunori Fujisawa
Main shock of a strong earthquake is often preceded by several foreshocks. To accommodate this fact in the study, two foreshocks and one main shock were used as earthquake loadings. The earthquake loadings were applied in the form of sinusoidal acceleration waves at the bottom of the soil box. Duration and frequency were same for the main shock and the foreshocks. The frequency was 15 Hz (corresponds to 0.6 Hz in the prototype) and the duration of the earthquake loading was 8 s (corresponds to 181 s ≈ 3 min in the prototype scale). The acceleration amplitude for the main shock was 0.4 g (corresponds to 0.4 g). The acceleration amplitude for the first and second foreshock was 0.1 g (corresponds to 0.1 g) and 0.2 g (corresponds to 0.2 g), respectively. The foreshocks and main shock were applied sequentially to the model. A time gap was provided between two consecutive loadings to dissipate the EPWP in the foundation ground (seabed soil and the mound).
Countermeasures for breakwater foundation subjected to foreshocks and main shock of earthquake loading
Published in Marine Georesources & Geotechnology, 2018
Babloo Chaudhary, Hemanta Hazarika, Siavash Manafi Khajeh Pasha
Main shock of earthquake is often preceded by number of foreshocks. To simulate such real ground situation, two foreshocks and one main shock were used for earthquake loadings. Earthquake loadings, in the form of sinusoidal acceleration waves, were provided at bottom of soil box. Frequency and duration were same for the main shock and the foreshocks. Frequency was 15 Hz, which corresponds to 0.6 Hz for prototype. Duration of earthquake loading was 8 s (corresponds to 181 s ≈ 3 min in prototype scale). Amplitudes of the accelerations were different for the main shock and the foreshocks. Amplitude of acceleration for the main shock was 0.4 g (corresponds to 0.4 g), and those for the foreshocks were 0.1 g (corresponds to 0.1 g) and 0.2 g (corresponds to 0.2 g). The earthquake loadings are shown in Figure 5. The earthquake loadings (foreshocks and main shock) were applied sequentially. Sufficient time gap was provided between two consecutive loadings to dissipate excess pore water pressure (EPWP) inside the foundation soil and the mound. The earthquake loadings for the main shock and the foreshocks are shown in Table 3.