Seismic microzoning from synthetic ground motion earthquake scenarios parameters: The case study of the city of Catania (Italy)

The city of Catania (Italy) in the South-Eastern Sicily has been affected in past times by several destroying earthquakes with high values of estimated magnitude. The seismogenic area to the south of Volcano Etna, known as Iblean Area, is placed between the African and the Euro-Asiatic plates on the west of the Ibleo-Maltese escarpment, to the south of the Graben of the Sicilian channel and on the east of the overlapping front of Gela. Basing on the seismic history of Catania, the following earthquake scenarios have been considered: the “Val di Noto” earthquake of January 11, 1693 (with intensity X-XI on MCS scale, magnitude M_W=7.41 and epicentral distance of about 13 km); the “Etna” earthquake of February 20, 1818 (with intensity IX on MCS scale, magnitude M_W=6.23 and epicentral distance of about 10 km). The soil response analysis at the surface, in terms of time history and response spectra, has been obtained by 1-D equivalent linear models for about 1200 borings location available in the data-bank of the central area of Catania of about 50 km², using deterministic design scenario earthquakes as input at the conventional bedrock.Seismic microzoning maps of the city of Catania have been obtained in terms of different peak ground acceleration at the surface and in terms of amplification ratios for given values of frequency.     

DIRDOP: a directivity approach to determining the seismic rupture velocity vector

Directivity effects are a characteristic of seismic source finiteness and are a consequence of the rupture spread in preferential directions. These effects are manifested through seismic spectral deviations as a function of the observation location. The directivity by Doppler effect method permits estimation of the directions and rupture velocities, beginning from the duration of common pulses, which are identified in waveforms or relative source time functions. The general model of directivity that supports the method presented here is a Doppler analysis based on a kinematic source model of rupture (Haskell, Bull Seismol Soc Am 54:1811–1841, 1964) and a structural medium with spherical symmetry. To evaluate its performance, we subjected the method to a series of tests with synthetic data obtained from ten typical seismic ruptures. The experimental conditions studied correspond with scenarios of simple and complex, unilaterally and bilaterally extended ruptures with different mechanisms and datasets with different levels of azimuthal coverage. The obtained results generally agree with the expected values. We also present four real case studies, applying the method to the following earthquakes: Arequipa, Peru (M _w = 8.4, June 23, 2001); Denali, AK, USA (M _w = 7.8; November 3, 2002); Zemmouri–Boumerdes, Algeria (M _w = 6.8, May 21, 2003); and Sumatra, Indonesia (M _w = 9.3, December 26, 2004). The results obtained from the dataset of the four earthquakes agreed, in general, with the values presented by other authors using different methods and data.     

Patterns of significant seismic quiescence on the Mexican Pacific coast

Many authors have proposed that the study of seismicity rates is an appropriate technique for evaluating how close a seismic gap may be to rupture. We designed an algorithm for identification of patterns of significant seismic quiescence by using the definition of seismic quiescence proposed by Schreider (1990). This algorithm shows the area of quiescence where an earthquake of great magnitude may probably occur. We have applied our algorithm to the earthquake catalog on the Mexican Pacific coast located between 14 and 21 degrees of North latitude and 94 and 106 degrees West longitude; with depths less than or equal to 60 km and magnitude greater than or equal to 4.3, which occurred from January, 1965 until December, 2014. We have found significant patterns of seismic quietude before the earthquakes of Oaxaca (November 1978, M_w = 7.8), Petatlán (March 1979, M_w = 7.6), Michoacán (September 1985, M_w = 8.0, and M_w = 7.6) and Colima (October 1995, M_w = 8.0). Fortunately, in this century earthquakes of great magnitude have not occurred in Mexico. However, we have identified well-defined seismic quiescences in the Guerrero seismic-gap, which are apparently correlated with the occurrence of silent earthquakes in 2002, 2006 and 2010 recently discovered by GPS technology.     

The moment magnitude <Emphasis Type="Italic">M</Emphasis><Subscript>w</Subscript> and the energy magnitude <Emphasis Type="Italic">M</Emphasis><Subscript>e</Subscript>: common roots and differences

Starting from the classical empirical magnitude-energy relationships, in this article, the derivation of the modern scales for moment magnitude M _w and energy magnitude M _e is outlined and critically discussed. The formulas for M _w and M _e calculation are presented in a way that reveals, besides the contributions of the physically defined measurement parameters seismic moment M ₀ and radiated seismic energy E _S, the role of the constants in the classical Gutenberg–Richter magnitude–energy relationship. Further, it is shown that M _w and M _e are linked via the parameter Θ = log(E _S/M ₀), and the formula for M _e can be written as M _e = M _w + (Θ + 4.7)/1.5. This relationship directly links M _e with M _w via their common scaling to classical magnitudes and, at the same time, highlights the reason why M _w and M _e can significantly differ. In fact, Θ is assumed to be constant when calculating M _w. However, variations over three to four orders of magnitude in stress drop Δσ (as well as related variations in rupture velocity V _R and seismic wave radiation efficiency η _R) are responsible for the large variability of actual Θ values of earthquakes. As a result, for the same earthquake, M _e may sometimes differ by more than one magnitude unit from M _w. Such a difference is highly relevant when assessing the actual damage potential associated with a given earthquake, because it expresses rather different static and dynamic source properties. While M _w is most appropriate for estimating the earthquake size (i.e., the product of rupture area times average displacement) and thus the potential tsunami hazard posed by strong and great earthquakes in marine environs, M _e is more suitable than M _w for assessing the potential hazard of damage due to strong ground shaking, i.e., the earthquake strength. Therefore, whenever possible, these two magnitudes should be both independently determined and jointly considered. Usually, only M _w is taken as a unified magnitude in many seismological applications (ShakeMap, seismic hazard studies, etc.) since procedures to calculate it are well developed and accepted to be stable with small uncertainty. For many reasons, procedures for E _S and M _e calculation are affected by a larger uncertainty and are currently not yet available for all global earthquakes. Thus, despite the physical importance of E _S in characterizing the seismic source, the use of M _e has been limited so far to the detriment of quicker and more complete rough estimates of both earthquake size and strength and their causal relationships. Further studies are needed to improve E _S estimations in order to allow M _e to be extensively used as an important complement to M _w in common seismological practice and its applications.     

Temporal and spatial variations of seismicity scaling behavior in Southern México

R/S analysis is used in this work to investigate the fractal correlations in terms of the Hurst exponent for the 1998–2011 seismicity data in Southern Mexico. This region is the most seismically active area in Mexico, where epicenters for severe earthquakes (e.g., September 19, 1985, M_w = 8.1) causing extensive damage in highly populated areas have been located. By only considering the seismic events that meet the Gutenberg–Ritcher law completeness requirement (b = 0.97, M_GR = 3.6), we found time clustering for scales of about 100 and 135 events. In both cases, a cyclic behavior with dominant spectral components at about one cycle per year is revealed. It is argued that such a one-year cycle could be related to tidal effects in the Pacific coast. Interestingly, it is also found that high-magnitude events (M_w ≥ 6.0) are more likely to occur under increased interevent correlations with Hurst exponent values H > 0.65. This suggests that major earthquakes can occur when the tectonic stress accumulates in preferential directions. In contrast, the high-magnitude seismic risk is reduced when stresses are uniformly distributed in the tectonic shell. Such cointegration between correlations (i.e., Hurst exponent) and macroseismicity is confirmed for spatial variations of the Hurst exponent. In this way, we found that, using the Hurst exponent standpoint, the former presumed Michoacan and the Guerrero seismic gaps are the riskiest seismic zones. To test this empirical finding, two Southern Mexico local regions with large earthquakes were considered. These are the Atoyac de Alvarez, Guerrero (M_w = 6.3), and Union Hidalgo, Oaxaca (M_w = 6.6), events. In addition, we used the Loma Prieta, California, earthquake (October 17, 1989, M_w = 6.9) to show that the high-magnitude earthquakes in the San Andreas Fault region can also be linked to the increments of determinism (quantified in terms of the Hurst exponent) displayed by the stochastic dynamics of the interevent period time series. The results revealed that the analysis of seismic activity by means of R/S analysis could provide further insights in the advent of major earthquakes.     

The <Emphasis Type="Italic">M</Emphasis><Subscript>w</Subscript> 3.1–4.7 earthquakes in the southern Baltic Sea and adjacent areas in 2000, 2001 and 2004

The area south and east of the Baltic Sea has very minor seismic activity. However, occasional events occur as illustrated by four events in recent years, which are analysed in this study: near Wittenburg, Germany, on May 19, 2000, M _w = 3.1, near Rostock, Germany, on July 21, 2001, M _w = 3.4 and in the Kaliningrad area, Russia, two events on September 21, 2004 with M _w = 4.6 and 4.7. Locations, magnitudes (M _L and M _w) and focal mechanisms were determined for the two events in Germany. Synthetic modeling resulted in a well-confined focal depth for the Kaliningrad events. The inversion of macroseismic observations provided simultaneous solutions of the location, focal depth and epicentral intensity. The maximum horizontal compressive stress orientations obtained from focal mechanism solutions, approximately N–S for the two German events and NNW–SSE for the Kaliningrad events, show a good agreement with the regionally oriented crustal stress field.     

Peak and integral seismic parameters of L��Aquila 2009 ground motions: observed versus code provision values

The M _w 6.3 L’Aquila earthquake of April 6, 2009 hit a wide area of the Abruzzo region (Central Italy). The epicentre of the main shock was very close to the urban centre of L’Aquila, the regional capital, with an epicentral distance less than 10 km. It was the strongest earthquake ever recorded in Italy which has provided ground motion recordings from accelerometric stations located in close proximity to the epicentre. Because of this, several remarkable results can be achieved by analysing the strong motion recorded signals in terms of peak (PGA, PGV and PGD) and integral (Housner Intensity, I _H) seismic parameters. Additionally, an alternative time-domain representation of recorded signals has been used to furnish a rapid comparison of traces recorded at different stations and along different directions. Some comparisons between the response spectra derived from the recordings and the elastic demand spectra provided in the new seismic Italian code have also been performed. PGA recorded values are very high and generally higher than code values for seismic actions with return period T _R = 475 years. In some cases, this also happens for seismic actions with T _R up to 2,475 years. With regard to I _H, recorded values are generally higher for T _R = 475 years, whilst they are remarkably lower for T _R = 2,475 years. Accurate analyses have been carried out in the article to better understand the above differences and their significance and implications.     

Spectral magnitude and seismic radiated energy computed from CDSN records

We have employed 10 digital records and computed the spectral magnitude and the seismic radiated energy for 18 large earthquakes (M _s≥6) occurred in Eur-asian belt during 1986–1989. The nine digital stations (CD-SN) distribute all over China and one in Germany. The spectral magnitudes of various period have different stability among stations. The stability is better for maximum spectral magnitudemi and seismic radiated energyE, their differences among stations are smaller, especially for the stations where the ray path main penetrates the low mantle. But the stability of corner period is usually not good. The relation between seismic radiated energy and seismic moment magnitudeM _w is lg (E)=1.5Mw+c, wherec is a constant. The maximum spectral magnitudemi=M _w+0.1, it is consistant with theoretical prediction. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 418–426, 1993. This work supported by the Deutsche Forschungsgemeinschaft, Bonn, F. R. Germany. The support is grateful acknowledge.     

Modeling the strong ground motion and rupture characteristics of the March 31, 2006, Darb-e-Astane earthquake,Iran, using a hybrid of near-field SH-wave and empirical Green’s function method

We analyze the strong motion accelerograms of the moderate (M _w = 6.1), March 31, 2006, Darb-e-Astane earthquake of western Iran and also those of one of its prominently recorded, large (M _w = 5.1) foreshock and (M _w = 4.9) aftershock. (1) Using derived SH-wave spectral data, we first objectively estimate the parameters W _o\mathit{\Omega} _{\rm o} (long period spectral level), f _c (corner frequency) and Q(f) (frequency dependent, average shear wave quality factor), appropriate for the best-fit Brune ω ^− 2 spectrum of each of these three events. We then perform a non-linear least square analysis of the SH-wave spectral data to provide approximate near-field estimates of the strike, dip, and rake of the causative faults and also the seismic moment, moment magnitude, source size, and average stress drop of these three events. (2) In the next step, we use these approximate values and an empirical Green’s function approach, in an iterative manner, to optimally model the strong ground motion and rupture characteristics of the main event in terms of peak ground acceleration/velocity/displacement and duration of ground shaking and thereby provide improved, more reliable estimates of the causative fault parameters of the main event and its asperities. Our near-field estimates for both the main moderate event and the two smaller events are in good conformity with the corresponding far-field estimates reported by other studies.     

Microzonation of Bucharest: State-of-the-Art

— The 1940 (M_w=7.7) and 1977 (M_w=7.4) Vrancea earthquakes (Romania) inflicted heavy damage and casualties in Bucharest and the statistics indicate a recurrence interval of 25 years for M_w 7.0 events. Under these circumstances, the seismic microzonation represents important information for detailed urban planning that establishes an appropriate level of preparedness to the earthquake threat. This paper reviews the main studies concerning the seismicity of the Vrancea region, the site conditions of the city, the characterization of the building stock, and the codes of practice that regulate the antiseismic design. The first-order microzonation of Bucharest was performed starting from the existing database of structural and geotechnical parameters. New insights originating from direct instrumental observation and interpretation of the local effects as well as realistic numerical modeling that update and improve the input data necessary for a detailed microzoning map of the city are also discussed.     

Seismic response analysis of multidrum classical columns

This paper presents a numerical investigation on the seismic response of multidrum classical columns. The motivation for this study originates from the need to understand: (a) the level of ground shaking that classical multidrum columns can survive, and (b) the possible advantages or disadvantages of retrofitting multidrum columns with metallic shear links that replace the wooden poles that were installed in ancient times. The numerical study presented in this paper is conducted with the commercially available software Working Model 2D?, which can capture with fidelity the sliding, rocking, and slide‐rocking response of rigid‐body assemblies. This paper validates the software Working Model by comparing selected computed responses with scarce analytical solutions and the results from in‐house numerical codes initially developed at the University of California, Berkeley, to study the seismic response of electrical transformers and heavy laboratory equipment. The study reveals that relative sliding between drums happens even when the g‐value of the ground acceleration is less than the coefficient of friction, µ, of the sliding interfaces and concludes that: (a) typical multidrum classical columns can survive the ground shaking from strong ground motions recorded near the causative faults of earthquakes with magnitudes M_w=6.0–7.4; (b) in most cases multidrum classical columns free to dislocate at the drum interfaces exhibit more controlled seismic response than the monolithic columns with same size and slenderness; (c) the shear strength of the wooden poles has a marginal effect on the sliding response of the drums; and (d) stiff metallic shear links in‐between column drums may have an undesirable role on the seismic stability of classical columns and should be avoided. Copyright © 2005 John Wiley & Sons, Ltd.     

Source characteristics of the deep Philippine earthquake cluster, 23 and 24 July 2010

We determine the rupture velocity, rupture area, stress drop and duration of four strong deep-focus earthquakes in the Philippines by back-projecting the teleseismic P waves. Four deep-focus earthquakes occurred in a totally consumed Molucca microplate; their focal depths were greater than 550 km and their moment magnitudes were between M _w 6.6 and M _w 7.6. By studying this deep-focus cluster, we are able to estimate the rupture velocity, rupture area and stress drop which would assist in constraining the physical mechanism for earthquakes deeper than 500 km. Since the Molucca microplate is totally consumed, little evidence is left on the surface for us to do research. This deep-focus cluster provides us the opportunity to reveal the properties of this totally consumed microplate by using seismic method for the first time. Four earthquakes in this deep-focus cluster all have multiple rupture subevents. The M _w 7.3 event ruptures in two subevents, the M _w 7.6 and M _w 7.4 events both have three subevents. The M _w 6.6 event has single peak on the amplitude as a function of time; however, its energy releases at two spatially separated areas. Our results show that this deep-focus cluster has a slow rupture velocity which is about 0.27 to 0.43 of the shear wave velocity, long-scaled duration, concentrated energy release area, and high stress drop. These source properties are similar to those of other deep earthquakes occurring in warm slabs and indicate that the totally consumed Molucca microplate possibly is a warm plate.     

Seismic microzonation studies for the city of Ragusa (Italy)

The seismic history of the city of Ragusa (Italy), the geotechnical characterisation of the subsoil and the site response analysis should be correctly evaluated for the definition of the Seismic Geotechnical Hazard of the city of Ragusa, through geo-settled seismic microzoning maps. Basing on the seismic history of the city of Ragusa, the following earthquake scenarios have been considered: the “Val di Noto” earthquake of January 11, 1693 (with intensity X–XI on MCS scale, magnitude M_W=7.41 and epicentral distance of about 53 km); the “Etna” earthquake of February 20, 1818 (with intensity IX on MCS scale, magnitude M_W=6.23 and epicentral distance of about 64 km); the Vizzini earthquake of April 13, 1895 (with intensity I=VII–VIII on MCS scale, magnitude M_W=5.86 and epicentral distance of about 26 km); the “Modica” earthquake of January 23, 1980 (with intensity I=V–VI on MCS scale, magnitude M_W=4.58 and epicentral distance of about 10 km); the “Sicilian” earthquake of December 13, 1990 (with intensity I=VII on MCS scale, magnitude M_W=5.64 and epicentral distance of about 50 km). Geotechnical characterisation has been performed by in situ and laboratory tests, with the definition of shear wave velocity profiles in the upper 30 m of soil. Soil response analyses have been evaluated for about 120 borings location by some non-linear 1-D models. Finally the seismic microzonation of the city of Ragusa has been obtained in terms of maps with different peak ground acceleration at the surface; shaking maps for the central area of the city of Ragusa were generated via GIS for the earthquake scenarios.     

Evidence of significant forward rupture directivity aggravated by soil response in an Mw6 earthquake and the effects on monuments

While strong directivity effects have been mostly recognized in M_w > 6.5 earthquakes, the paper investigates the case of a strong such effect in a relatively small‐magnitude event on 3 February 2014 in the island of Cephalonia, Greece. The second of two events (both of M_w ≈ 6) produced a pernicious accelerogram in the region's main town, Lixouri. The paper provides evidence from geology, interferometry, and seismology to convince that the motion was the result of constructive interference in front of the direction of rupture of the obliquely‐strike‐slip fault. The nature of the record is explored to demonstrate that its frequency content, its high velocity pulse, and its strong fault‐normal (FN) favorable polarity are associated with directivity. Moreover, the broad spectral acceleration peak (of 1.7 g) of the FN motion, centered at a period (T ≈ 1.4 s) which almost coincides with the period of the velocity pulse, is shown to have also been affected by soil amplification, in quantitative agreement with Bray et al. (2009). Such a directivity‐and‐soil‐affected motion explains much of the profound damage to monuments, slopes, and harbor quaywalls. In particular, toppling (as well as excessive rotation and sliding) of nearly‐all the tombstones in Lixouri cemetery are shown to correlate well with characteristics of the FN component of motion. By contrast, the excellent performance of the building stock — despite the destructive shaking that prevailed — is persuasively attributed to conservatively‐robust construction practices of the past and the high base shear coefficient of the strict latest (2000) seismic code. Copyright © 2017 John Wiley & Sons, Ltd.     

Deterministic Approach for the Seismic Microzonation of Bucharest

— The mapping of the seismic ground motion in Bucharest, due to the strong Vrancea earthquakes is carried out using a complex hybrid waveform modeling method which combines the modal summation technique, valid for laterally homogeneous anelastic media, with finite-differences technique, and optimizes the advantages of both methods. For recent earthquakes, it is possible to validate the modeling by comparing the synthetic seismograms with the records. We consider for our computations the frequency range from 0.05 to 1.0 Hz and control the synthetic signals against the accelerograms of the Magurele station, low-pass filtered with a cut-off frequency of 1.0 Hz of the 3 last major strong (M_w > 6) Vrancea earthquakes. Using the hybrid method with a double-couple seismic source approximation, scaled for the source dimensions and relatively simple regional (bedrock) and local structure models, we succeeded in reproducing the recorded ground motion in Bucharest at a satisfactory level for seismic engineering. Extending the modeling to the entire territory of the Bucharest area, we construct a new seismic microzonation map, where five different zones are identified by their characteristic response spectra.     

Real-time mapping of earthquake-induced landslides

Rigid sliding block analysis is a common analytical procedure used to predict the potential for earthquake-induced landslides for natural slopes. Currently, predictive models provide the expected level of displacement as a function of the characteristics of the slope (e.g., geometry, strength, yield acceleration) and the characteristics of earthquake shaking (e.g., peak ground acceleration, peak ground velocity). These predictive models are used for developing seismic landslide hazard maps which identify zones with risk of earthquake-induced landslides. Alternatively, these models can be combined with Shakemaps to generate “near-real-time” Slidemaps which could be used, among others, as a tool in disaster management. Shakemaps (a publicly available free service of the United States Geological Survey, USGS) provide near-real-time ground motion conditions during the time of an earthquake event. The ground motion parameters provided by a Shakemap are very useful for the development of Slidemaps. By providing ground motion parameters from an actual earthquake event, Shakemaps also serve as a tool to decouple the uncertainty of the ground motion in sliding displacements prediction. Campania region in Italy is studied for assessing the applicability of using Shakemaps for regional landslide-risk assessment. This region is selected based on the availability of soil shear strength parameters and the proximity to the 1980 Irpina (M _w  = 6.9) Earthquake.     

Tsunami Measurements in Bays of Shikotan Island

Bottom pressure gauges deployed in bays of Shikotan Island (South Kuril Islands) recently recorded two tsunamis: the Simushir (Kuril Islands) tsunami of January 13, 2007 generated by a local earthquake with magnitude M _w = 8.1 and the Peruvian tsunami of August 15, 2007 generated by a distant earthquake, M _w = 8.0. The records enabled us to investigate the properties of these two tsunamis and to estimate the effect of the regional and nearshore topography on arriving tsunami waves. Eigen periods and spatial structure of resonant oscillations in particular bays were examined based on results of numerical modeling. Significant amplification of the fundamental (Helmholtz) resonant modes in Malokurilskaya Bay (19 min) and in Krabovaya Inlet (29 min) and some secondary modes was caused by the Simushir tsunami. The considerably different geometry and bottom topography of these bays, located on the inner coast of the island, determine the differences in their eigen periods; the only mutual peak, which was found in both basins, had a period of 5 min and was probably related to the source features. The Peruvian tsunami was clearly recorded by the bottom pressure gauge in Tserkovnaya Bay on the outer (oceanic) coast of the island. Three dominant periods in the tsunami spectrum at this bay were 60, 30 and 19 min; the latter period was found to be related to the fundamental mode of the bay, while the other two periods appear to be associated with the shelf resonant amplification of tsunami waves arriving in the region of the South Kuril Islands. The prevalence of low-frequency components in the observed tsunami spectrum is probably associated with the large extension of the initial source area and faster decay of short period waves during the long trans-oceanic tsunami propagation.     

Ground motion attenuation relation for small to moderate earthquakes in Fujian region, China

We collect 1974 broad-band velocity records of 94 earthquakes (ML=2.8~4.9, △=13~462 km) from seven stations of the Fujian Seismic Network from March 1999 to March 2007. Using real-time simulation, we obtain the corresponding acceleration and then adopt different models to analyze the seismic data. As a result, a new attenuation relationship between PGA and PGV of the small and moderate earthquakes on bedrock site in Fujian region is established. The Yongchun earthquake occurred recently verifies the attenuation relationship well. This paper provides a new approach for studying the ground motion attenuation relationship using velocity records.     

Probabilistic Assessment of Earthquake Recurrence in Northeast India and Adjoining Regions

Northeast India and adjoining regions (20°–32° N and 87°–100° E) are highly vulnerable to earthquake hazard in the Indian sub-continent, which fall under seismic zones V, IV and III in the seismic zoning map of India with magnitudes M exceeding 8, 7 and 6, respectively. It has experienced two devastating earthquakes, namely, the Shillong Plateau earthquake of June 12, 1897 (M _w 8.1) and the Assam earthquake of August 15, 1950 (M _w 8.5) that caused huge loss of lives and property in the Indian sub-continent. In the present study, the probabilities of the occurrences of earthquakes with magnitude M ≥ 7.0 during a specified interval of time has been estimated on the basis of three probabilistic models, namely, Weibull, Gamma and Lognormal, with the help of the earthquake catalogue spanning the period 1846 to 1995. The method of maximum likelihood has been used to estimate the earthquake hazard parameters. The logarithmic probability of likelihood function (ln L) is estimated and used to compare the suitability of models and it was found that the Gamma model fits best with the actual data. The sample mean interval of occurrence of such earthquakes is estimated as 7.82 years in the northeast India region and the expected mean values for Weibull, Gamma and Lognormal distributions are estimated as 7.837, 7.820 and 8.269 years, respectively. The estimated cumulative probability for an earthquake M ≥ 7.0 reaches 0.8 after about 15–16 (2010–2011) years and 0.9 after about 18–20 (2013–2015) years from the occurrence of the last earthquake (1995) in the region. The estimated conditional probability also reaches 0.8 to 0.9 after about 13–17 (2008–2012) years in the considered region for an earthquake M ≥ 7.0 when the elapsed time is zero years. However, the conditional probability reaches 0.8 to 0.9 after about 9–13 (2018–2022) years for earthquake M ≥ 7.0 when the elapsed time is 14 years (i.e. 2009).     

Lessons from the 2003 Tokachi-oki, Japan, earthquake for prediction of long-period strong ground motions and sloshing damage to oil storage tanks

The 2003 Tokachi-oki earthquake (M _w 8.0) in northern Japan generated large-amplitude long-period (4–8 s) ground motions in the Yufutsu sedimentary basin, causing severe damage to seven large oil storage tanks with floating roof structures because of severe sloshing of oil. The 30,000–40,000-m³ tanks having suffered the severe damage such as fires and sinking of floating roofs experienced the sloshing with large amplitudes exceeding 3 m in which the fundamental mode was predominant. The second mode of sloshing was also excited in the 110,000-m³ tanks in which their floating roofs sank into oil, indicating that the higher modes of sloshing as well as the fundamental mode should be considered in damage prediction. The strong ground motion recordings demonstrated the earthquake dependency of predominant periods and the substantial spatial variation of the long-period shaking observed within the Yufutsu basin, meaning the necessity of source- and site-specific prediction of long-period strong ground motions. The two-dimensional numerical modeling suggested the importance of detailed structures of soft near-surface sediments as well as deep basin structure for accurate prediction of long-period strong ground motions in deep sedimentary basins.