China
Africa
Explore chapters and articles related to this topic
Earthquake activity
Published in F.G. Bell, Geological Hazards, 1999
The values of the constants a and b have been modified several times as data have accumulated. In the case of surface and body waves the corresponding equations are respectively: ()logE=12.24+1.44Ms and ()logE=4.78+2.57mb where E is given in ergs. The seismic moment, Mo, is related to the area of rupture, A, the rigidity modulus, μ, of the faulted rock, and the average dislocation, u, caused by an earthquake as follows: ()Mo=Auμ
Seismology and site effects
Published in Mark Aschheim, Enrique Hernández-Montes, Dimitrios Vamvatsikos, Design of Reinforced Concrete Buildings for Seismic Performance, 2019
Mark Aschheim, Enrique Hernández, Dimitrios Vamvatsikos
Another measure of magnitude, the moment magnitude (Mw), overcomes the mentioned limitations. Mw is based on the concept of seismic moment, and it is uniformly applicable to all sizes of earthquakes. The seismic moment (M0) is a measure of the size of an earthquake based on the area of fault rupture, the average displacement across the fault rupture surface, and the force that was required to overcome the friction across the fault surface (Figure 2.7). Seismic moment can also be calculated from the amplitude spectra of seismic waves.
Earthquake data and source models
Published in Sreevalsa Kolathayar, T.G. Sitharam, Earthquake Hazard Assessment, 2018
Sreevalsa Kolathayar, T.G. Sitharam
Unfortunately, many of the magnitude scales are limited by saturation toward large earthquakes with mb > 6.0, ML > 6.5, and MS > 8.0. The existence of different magnitude scales necessitates the conversion of these magnitude scales to a single magnitude scale for analysis purposes. The moment magnitude (Kanamori, 1977) can represent the true size of earthquakes because it is based on the seismic moment, which, in turn, is proportional to the product of the rupture area and dislocation of an earthquake fault (Aki, 1966). MW is defined as: MW=2/3log10M0−6.05 where M0 is the scalar seismic moment in Nm. The homogenization of the earthquake catalog involves expressing the earthquake magnitudes in one common scale. Practical problems, such as seismic hazard assessment, necessitate the use of a homogenized catalog. Because MW does not saturate, it is the most reliable magnitude scale for describing the size of an earthquake (Scordilis, 2006). Given that the moment magnitude scale is the most advanced and widely used magnitude scale, the original magnitudes of Indian earthquakes in different time periods have been converted to unified MW magnitudes. Several relations were proposed by different researchers to convert different magnitude scales to MW (Nuttli, 1983; Giardini, 1984; Kiratzi et al., 1985; Heaton et al., 1986; Patton and Walter, 1993; Johnston, 1996; Papazachos et al., 2002; Scordilis, 2006; Thingbaijam et al., 2008; among many others). In this study, two methods for magnitude conversion were used; one based on Scordilis (2006) and the other using the developed correlations from the data available for the study area (as detailed below).
Enhanced Seismic Response Prediction of Critical Structures via 3D Regional Scale Physics-Based Earthquake Simulation
Published in Journal of Earthquake Engineering, 2023
M. Korres, F. Lopez-Caballero, V. Alves Fernandes, F. Gatti, I. Zentner, F. Voldoire, D. Clouteau, D. Castro-Cruz
Concerning the second verification model, the extended fault of km has a strike of , dip of , rake of and its hypocenter is located at (2164 m, 0 m, −1772 m) (Fig. 6a). Total seismic moment of the extended fault is equivalent to N.m (). The time distribution of the seismic moment based on the position of different sub-sources of the fault is given in Fig. 6b. The maximum slip generated from the fault is around 0.06 m and the slip distribution along with the triggering time is given in Fig. 6c, while the source time function is provided in Fig. 6d. The rupture process of this kinematic source is based on a waveform inversion procedure with the empirical Green function (EGF) as described in Ide (2001).
Why the M w 6 parkfield earthquake expected in the 1985–1993 interval was postponed till 2004?
Published in Geomatics, Natural Hazards and Risk, 2022
Xuezhong Chen, Yane Li, Lijuan Chen
The results of laboratory experiments indicate a reverse relation between b-value and stress (Scholz 1968a; Wyss 1973). Fluctuations of b are also related to the degree of material heterogeneity(Mogi 1962), even geothermal gradients(Warren and Latham 1970). The apparent stress is a product of the shear modulus and the ratio of seismic energy to seismic moment, equals to a product of seismic efficiency and the average stress on the focal fault(Wyss 1970; Wyss and Molnar 1972). When the tectonic stress increases, the b-value deceases, meanwhile the apparent stress increases and vice versa, i.e. there also exists an inverse correlation between b-value and apparent stress. As a consequence, by conducting joint analysis of b-value and apparent stress the stress at the focal source can be indirectly detected with other influencing factors excluded. Observations of earthquake case have recently showed that the b-value decreased and the apparent stress increased several years before the occurrence of strong earthquakes(Chen et al. 2021a; Li and Chen 2021; Li et al. 2021a). Observations also showed the b-value decreasing with duration of months and years prior to some earthquakes(Wyss 1973; Imoto 1991; Nakaya 2006; Xie et al. 2010; Nanjo 2020; Shi et al. 2018; Chen and Zhu 2020; Chen et al. 2022; Chen et al. 2021b), which is interpreted in the form of stress increasing before an approaching seismic event(Scholz 1968b; Main et al. 1989; Urbancic et al. 1992; Hainzl et al. 1999; Nuannin et al. 2005).
Study on fault slip dynamic response and rock burst potential under the influence of different horizontal stresses
Published in Geomatics, Natural Hazards and Risk, 2022
Peng Kong, Anying Yuan, Yanqing Liu, Zhihong Li
Figure 7 shows the evolution law of fault slip seismic moment under different horizontal stress conditions. It can be seen from Figure 7 that there are great differences between normal and reverse fault slip seismic moment affected by mining. For normal faults, when the working face advanced to 40 m away from the fault, the fault begins to slip and releasing the fault slip seismic source under the influence of mining, but the energy level of the fault slip seismic source was small. As the working face approaches the fault, the seismic moment of fault slip increases. When the working face advanced to the fault position, the seismic moment of fault slip reaches the maximum value of 9.9 × 1011。When mining the panel through the reverse fault, the fault starts to release the fault slip moment source when the working face advances to 20 m distance from the fault. When the working face advanced to 10 m distance from the fault, the fault slip seismic moment increases significantly to 1.45 × 1012. By comparing the seismic moment of normal fault and reverse fault, it can be seen that the normal fault is more likely to slip and release seismic source after mining, but the energy released by normal fault slip is less than that of reverse fault.