Shaking is Almost Always a Surprise: The Earthquakes That Produce Significant Ground Motion

2020 ◽  
Vol 92 (1) ◽  
pp. 460-468
Author(s):  
Sarah E. Minson ◽  
Annemarie S. Baltay ◽  
Elizabeth S. Cochran ◽  
Sara K. McBride ◽  
Kevin R. Milner
Keyword(s):  
Ground Motion ◽  
Strong Ground Motion ◽  
Natural Variability ◽  
Significant Source ◽  
Relative Impact ◽  
Frequency Relationship ◽  
Large Earthquakes ◽  
Strong Ground

Abstract Although small earthquakes are expected to produce weak shaking, ground motion is highly variable and there are outlier earthquakes that generate more shaking than expected—sometimes significantly more. We explore datasets of M 0.5–8.3 earthquakes to determine the relative impact of frequent, smaller-magnitude earthquakes that rarely produce strong ground motion, to rare, large earthquakes that always cause strong shaking. We find that the natural variability of ground motion, combined with the Gutenberg–Richter magnitude–frequency relationship, ensures that most occurrences of any ground motion come from earthquakes of smaller magnitude than expected, often >2 magnitude units smaller. This holds even for very strong shaking (>20%g), suggesting that M<7 earthquakes could be a significant source of damage.

High-Frequency Spectral Decay Characteristics of Seismic Records of Inland Crustal Earthquakes in Japan: Evaluation of the fmax and κ Models

2020 ◽  
Vol 110 (2) ◽  
pp. 452-470
Author(s):  
Masato Tsurugi ◽  
Reiji Tanaka ◽  
Takao Kagawa ◽  
Kojiro Irikura
Keyword(s):  
Ground Motion ◽  
High Frequency ◽  
Strong Ground Motion ◽  
Cutoff Frequency ◽  
Source Model ◽  
Power Coefficient ◽  
Crustal Earthquakes ◽  
Log Linear ◽  
Large Earthquakes ◽  
Strong Ground

ABSTRACT We examined high-frequency spectral decay characteristics of ground motions for inland crustal earthquakes in Japan, which are important in strong ground motion predictions. We examined 105 earthquakes (Mw 3.3–7.1), including seven large earthquakes (Mw 5.9–7.1). Spectral decay characteristics were accurately evaluated assuming the ω-squared source model and using two approaches: the fmax model (commonly used in Japan), described by the cutoff frequency fmax and the power coefficient of spectral decay s, and the κ model (commonly used in worldwide), the exponential spectral decay model, described by the parameter κ and the specific frequency fE at which a spectrum starts to decrease linearly with increasing frequency in log–linear space. For large earthquakes, we estimated fmax to range from 6.5 to 9.9 Hz and s from 0.78 to 1.60 in the fmax model, and κ to range from 0.014 to 0.051 s and fE from 2 to 4.5 Hz in the κ model. In both approaches, we found that the spectral decay characteristics are regionally dependent. fmax in the fmax model and fE in the κ model tended to be smaller for large earthquakes than for moderate and small earthquakes, clearly demonstrating a seismic moment dependency. We confirmed positive correlations between equivalent parameters of the two approaches, that is, between s and κ and between fmax and fE. Moreover, we found that both approaches are appropriate for evaluating spectral decay characteristics, as long as the spectral decay parameters are appropriately evaluated by comparison with observed spectra. We examined the effects of the spectral decay characteristics on strong ground motion predictions, and demonstrated that simulated motions corrected using the fmax model and those corrected using the κ model are almost the same. The results presented in this article contribute to improving predictions of high-frequency strong ground motion.

Use of empirical Green's functions, spectral ratios, and kinematic source models for simulating strong ground motion

1996 ◽  
Vol 86 (3) ◽  
pp. 597-615 ◽  
Author(s):  
R. A. W. Haddon
Keyword(s):  
Ground Motion ◽  
Strong Ground Motion ◽  
Ground Motions ◽  
Spectral Characteristics ◽  
Spectral Ratios ◽  
Spectral Models ◽  
Lg Wave ◽  
Wave Trains ◽  
Large Earthquakes ◽  
Strong Ground

Abstract Ground motions for large and moderately large earthquakes at short and moderate distances are particularly important for seismic hazard estimation in eastern North America (ENA). Very few direct observations of such ground motions have been obtained, however, because of the sparsity of recording sites and the relatively low rates of occurrence of large earthquakes inside the region. Estimation of strong ground motion must therefore rely heavily on theoretical models to extend empirical results obtained from small earthquakes and from the few larger ones for which reliable data are available. Because of the generally large distances between recording stations, the main source of useful data comes from Lg wave trains observed at relatively large distances. For the two largest earthquakes to have occurred near populated regions of southeastern Canada during the past decade, spectral ratios of the Lg wave trains of the mainshocks, with respect to those of their aftershocks, are found to depend almost entirely upon the source radiation characteristics of the sources alone. This result is utilized to derive elastodynamically-based kinematic rupture models that are consistent with the empirical spectral ratio data. Such models provide a firm physical basis from which to infer the most probable spectral characteristics for future large earthquakes in the region. In converse application, it is shown that spectral ratios obtained from such models, along with empirical seismograms from small earthquakes, can be used to accurately simulate strong ground motions at short and moderate (as well as large) distances. As such small-event seismograms are relatively plentiful, the problem of reliable strong ground motion estimation is therefore reduced to that of obtaining reliable representative source spectral models. The solution of this latter problem must continue to depend upon whatever empirical data are available and upon appropriately detailed theoretical modeling.

Special Issue on Strong Ground Motion Prediction and Seismic Hazard Assessment

2013 ◽  
Vol 8 (5) ◽  
pp. 847-847
Author(s):  
Hiroyuki Fujiwara
Keyword(s):  
Seismic Hazard ◽  
Ground Motion ◽  
Hazard Assessment ◽  
Strong Ground Motion ◽  
Seismic Hazard Assessment ◽  
Hazard Maps ◽  
Special Issue ◽  
Strong Ground Motion Prediction ◽  
Large Earthquakes ◽  
Strong Ground

We have been conducting seismic hazard assessment for Japan under the guidance of the Headquarters for Earthquake Research Promotion of Japan since the 1995 Hyogo-ken Nanbu Earthquake, and have made National Seismic Hazard Maps for Japan for use in estimating strong ground motion caused by future earthquakes. This special issue reviews the results of these efforts. Such work includes the development of seismic hazard assessment methodology for Japan, highly accurate prediction techniques for strong seismic ground motion and modeling underground structures for evaluating strong ground motion. Related research on utilization initiatives and risk assessment based on hazard information has also been conducted. An open Web system – the Japan Seismic Hazard Information Station (J-SHIS) – has even been developed to provide information interactively. The 2011 Mw9.0 Great East Japan Earthquake was the largest such event recorded in the history of Japan. This megathrust earthquake was not considered in National Seismic Hazard Maps for Japan. But efforts toward revising seismic hazard assessment in Japan are progressing based on lessons learned from this earthquake. Hazard assessment is currently being reviewed in relation to the large earthquakes anticipated to occur in the near future based in the Sagami Trough and the Nankai Trough in the waters of offshore Japan. This assessment, which considers earthquakes larger than those assumed to have occurred in the past, is being reviewed as of this writing. In light of these pressing circumstances, studies are now being implemented to evaluate the long-period ground motion accompanying these large earthquakes. The knowledge that has been cultivated in Japan in terms of seismic hazard assessment has reached a high level, and it is important to expand such knowledge both internationally and domestically. This is just one of the reasons that efforts here in Japan are being made to help improve the level of seismic hazard assessment in the Asian region and throughout the entire world. It is expected that this special issue will help contribute to the further development of strong ground motion prediction and seismic hazard assessment now and in the future. Finally, I extend our sincere thanks to all of the contributors and reviewers involved with these articles.

Sign in / Sign up

Export Citation Format

Share Document