Shake Level Research Articles

Ground motion scaling in the Marmara region, Turkey

SUMMARY Predictive relationships for the ground motion in the Marmara region (northwestern Turkey) are parametrized after regressing three-component waveforms from regional earthquakes, in the frequency range: 0.4‐15.0 Hz, and in the distance range: 10‐200 km. The data set consists of 2400 three-component recordings from 462 earthquakes, recorded at 53 stations. Moment magnitudes, M w, range between 2.5 and 7.2. The largest event for which we have waveforms available (M w 7.2) occurred in Duzce on 1999 November 12. The aftershocks of that earthquake, together with the aftershocks of the 1999 August 17 Izmit event (M w = 7.4), are included in the dataset. Regressions are performed, independently, on Fourier velocity spectra and on peak ground velocities, for a large number of sampling frequencies. A simple model is used to relate the logarithm of the measured ground motion to excitation, site, and propagation terms. Results obtained for peak velocities are used to define a piecewise continuous geometrical spreading function, g(r), a frequency-dependent Q(f ), and a distance-dependent duration function. The latter is used, through random vibration theory (RVT), in order to predict time-domain characteristics (i.e. peak values) of the ground motion. The complete model obtained for the peak ground motion was used to match the results of the regressions on the Fourier amplitudes. Fourier velocity spectra for the combined horizontal motion are best fit by a hinged quadrilinear geometrical spreading function for observations in the 10‐200 km hypocentral distance ranges as a function of frequency: f 100, f ≥ 1.0 Hz, r −1.0 for r ≤ 30 km; r −0.6 for 30 100 km. The frequency-dependent crustal shearwave quality factor Q (f ) coefficient Q( f ) = 180 f 0.45 . The T (5‐75 per cent) duration window provides good agreement between observed and predicted peak values. By modelling the behaviour of the small earthquakes at high frequency, we also quantified a regional parameter κ = 0.055 s. Spectral models with one single-corner frequency (Brune), and with two-corner frequencies (Atkinson and Silva) fit the observed high-frequency excitation levels equally well, whereas the model by Atkinson and Silva fits the low-frequency observations slightly better than Brune’s. RVT is used to predict the absolute levels of ground shaking, following Boore’s implementation of the stochastic ground motion model (Boore’s SMSIM codes). Our regional empirical predictive relationships are compared to the ones adopted in several regions of the world, from California to Western United States.

Probabilistic Warning Times for Earthquake Ground Shaking in the San Francisco Bay Area

Current earthquake mitigation in the United States focuses on long-term characterization of the likely levels of ground shaking and the frequency of occurrence (Frankel et al. , 1996). These estimates are the basis for building codes, which aim to prevent collapse during earthquakes. In other countries, including Mexico, Japan, Taiwan, and Turkey, earthquake warning systems (EWS) are used in addition to building codes to further reduce the impact of earthquakes (Espinosa Aranda et al. , 1995; Wu et al. , 1998; Wu and Teng, 2002; Erdik et al. , 2003; Odaka et al. , 2003; Boese et al. , 2004; Kamigaichi, 2004; Nakamura, 2004; Horiuchi et al. , 2005; Wu and Kanamori, 2005). Short-term mitigation actions are taken to reduce both financial losses and casualties. Earthquake warning systems rapidly detect the initiation of earthquakes and warn of the forthcoming ground shaking. For a specific city, such as San Francisco, the warning time could be tens of seconds for some earthquakes but essentially zero seconds for others. Even in situations when San Francisco has zero seconds warning, however, neighboring cities such as Oakland would likely have a few seconds and San Jose would have ∼15 seconds warning. Thus, for any earthquake scenario in a densely populated region, such as the San Francisco Bay area (SFBA), an EWS could provide warning to at least some of the affected population in a damaging earthquake. Here I present estimates of the warning times that would be available for locations across the SFBA if an EWS were implemented in northern California. These warning times are calculated for identified likely earthquake scenarios in northern California. For each scenario an estimate of the probability of occurrence has been made (WGCEP, 2003), allowing calculation of probabilistic warning times. The …

Recorded Maximum Seismic Intensity Maps in Japan from 1586 to 2004

To evaluate the occurrence of large earthquakes and associated damaging ground motions, probabilistic ground-motion maps have been published for the United States, Japan, and other countries (Frankel et al. , 1996; Headquarters for Earthquake Research Promotion, 2005; Global Seismic Hazard Assessment Program, 1999). These maps are constructed by combining large amounts of data and model estimates of seismicity, distance attenuation, and local site response. A complementary map of maximum ground motion (intensity) also can be constructed empirically from a good record of historical intensity, for example, the compiled reports in Japan. Some past studies have used seismic intensities from historical earthquakes to quantify the expected level of strong shaking for Japan. Kawasumi (1951) used relations among intensity, magnitude, and acceleration to estimate expected maximum acceleration levels across Japan for periods of 75, 100, and 200 years. Kanai and Suzuki (1968), following a similar method, estimated peak velocity distributions. In another study of probabilistic hazards for Japan related to seismic intensities, Wesnousky et al. (1984) investigated the relationship among repeat times of earthquakes, seismic moment, and associated seismic intensity distribution using geologic-fault data and showed the probabilistic occurrence of earthquakes with intensity equal to or larger than JMA 5. However, the published probabilistic maps all depend largely on the models and inferences about the magnitudes and locations of historical earthquakes, which are diffi cult to verify fully. In this study we take the simple approach of directly mapping the maximum historical intensity distribution across Japan. We use the Japan Meteorological Agency (JMA) intensity, as observed by JMA and interpreted by Usami (2003). Historical records of earthquake damage in Japan extend back more than 1,000 years and provide a valuable resource for studying historical seismicity. We make no assumptions about earthquake location, magnitude-intensity relations, or earthquake occurrence models. This approach …

Simplified inverse dynamics models for MR fluid dampers

The magnetorheological (MR) damper is considered to be one of the most promising semi-active control devices for reduction of structural vibration. Due to the damper’s nonlinear characteristics, its inverse dynamics model is difficult to obtain. In this paper, a simplified approach, namely the simplified inverse dynamics (SID) model, has been developed for both the Bingham plasticity model and the Bouc–Wen hysteresis model. SID models have then been used to calculate the optimal fluid yield stress or input current, in order to realize the desirable control forces obtained from various optimal control algorithms. For each model, a piston velocity feedback (PVF) algorithm and a damper force feedback (DFF) algorithm have been formulated. The proposed model has been shown to be applicable to both small-scale and large-scale MR dampers. Also, different configurations of MR dampers, such as ones with different dimensions, coil resistances, types of MR fluid, have been employed to show the generic nature of the SID model. The effectiveness of force tracking using the SID model has been demonstrated through a series of numerical simulations. A multi-storey frame structure with MR damper–brace systems, using a large-scale 20-ton MR damper, has been adopted. Numerical results show that the MR damper with the proposed SID model can produce forces very close to the optimal control forces, and that the response reduction is very close to that for the case of fully active control. Also, equally high accuracy of force tracking for different shaking levels and frequency contents of ground motions can be observed. The results demonstrate that the SID model can be a simple, yet effective, tool for both research and application purposes.

Ground-Motion Amplification in Nonlinear Soil Sites with Uncertain Properties

This work presents a statistical study on the effect of soil layers with uncertain properties on ground-motion intensity at the soil surface. Surface motion is obtained by applying multiple real rock earthquake records at the base of different characterizations of the soil column, each one generated via Monte Carlo simulation. The effect of the soil is studied in terms of a site-specific, frequency-dependent amplification function, AF( f ), where f is a generic oscillator frequency. The goal here is the identification of ground-motion parameters that allow an efficient prediction of AF( f ). We investigated magnitude, M, source-to-site distance, R, of the input bedrock accelerogram along with bedrock ground-motion parameters such as peak ground acceleration, PGAr, and spectral acceleration values, and , both rr S ( f ) S ( f ) aa sc at the generic frequency f and at the specific initial fundamental frequency of vibra- tion, fsc of the soil column. This work includes two case studies: a saturated sandy site and a saturated soft clayey site. In the former, loss of shear strength owing to cyclic mobility is anticipated for severe levels of ground shaking, while in the latter, significant amplification is expected at long oscillator periods. The results show that of the input record is the single most helpful parameter for the prediction of r S ( f ) a AF( f ) at the same oscillator frequency, f. is more informative than PGAr and/ r S ( f ) a or the pair of M and R values of the event that generated the bedrock motion. A sufficiently accurate estimate of the median AF( f ) can be obtained by using 10 or fewer records, which may be selected without undue attention to the specific scenario events (i.e., M and R pairs) that control the hazard at the site. Finally, the effect of the uncertainty in the soil parameters on the prediction error of AF( f ) is of secondary importance compared to that from record-to-record variability. These findings will be used to estimate the hazard at the soil surface in a companion article in this issue (Bazzurro and Cornell, 2004).

Retesting of Liquefaction/Nonliquefaction Case Histories in the Imperial Valley

This paper describes the retesting of liquefaction and nonliquefaction field case histories in the Imperial Valley using the electric cone penetration test (CPT). Subsurface testing of the River Park and Heber Road sites first occurred following the 1979 Imperial Valley earthquake (Bennett et. al. 1981, Youd and Bennett 1983). These two sites are rich in information because they have experienced several earthquakes in recent history, have been subjected to moderate levels of strong ground shaking, the liquefiable layers have appreciable fines content, and the sites contain a number of high-quality nonliquefied data points. The recent liquefaction case history database for probabilistic assessment of liquefaction triggering by Moss et. al. (2003), is based primarily on data acquired using the modern electric cone following ASTM D5778. Case histories previously explored with a cone not adhering to current ASTM standards may introduce significant epistemic uncertainty into the assessment of liquefaction potential and are considered sub-optimal for probabilistic analysis purposes. This paper describes the acquisition and analysis of modern electric cone data at the Heber Road and River Park sites. These important sites can now be incorporated into the probabilistic CPT-based liquefaction case history database and used for back-analysis of liquefaction triggering. Discussed are the effects of ground motion character and frequency content on liquefaction at these two sites and how this influences the results using a simplified liquefaction procedure.

SURVEY OF RECENT REMEDIATION TECHNIQUES IN JAPAN, AND FUTURE APPLICATIONS

In Japan, many remediation methods against liquefaction have been developed since the 1964 Niigata earthquake. The methods are classified into two categories: Ground treatments to prevent liquefaction, and measure that strengthen structures to prevent or minimise damage if the ground liquefies. The remediation methods have been applied to many kinds of structures, such as oil tanks, quay walls, bridges and buildings. The effectiveness of ground treatments in preventing liquefaction has been proved during past earthquakes. However, the 1995 Kobe earthquake presented three problems: The applicability of current methods under very strong shaking (Level 2 earthquake motion), the introduction of a new design concept based on performance, and countermeasures against liquefaction-induced flow. Many studies on these problems have been conducted recently in Japan.

Response of seismically isolated buildings with buffers subjected to near-source ground motions and possible alternative isolation systems

The response of a seismically isolated building with lead rubber bearings (LRB) to near source ground motions from large earthquakes was investigated. The building was assumed to have a buffer to limit the maximum bearing displacement in a rare event of large magnitude and the buffer gap was assumed to be only 150mm (the level of maximum isolator displacement used in the 1980s). The structure was assumed to be designed for 1.5 times the NS component of the 1940 El Centro record. The 15% damped (an amount of damping which is close to the equivalent damping ratio for an seismically isolated building at its isolator design displacement) displacement spectrum of the design motion is only 40% that of the Sylmar County Hospital Parking Lot record from the 1994 Northridge earthquake (Mw= 6.7) in the period range around the first modal periods of both isolated and un-isolated structure used in the present study. Among the near-source records that are available, the near-source Sylmar record from the 1994 Northridge earthquake was found to have a very large displacement demand in a period range of 2.0 - 3.0s and this record is thought to be a better representation of the expected near-source motions than the 1.5 times the 1940 El Centro record. Structure-buffer impact was found to impose very large inter-storey drifts and produce very large storey accelerations, when the building was subjected to the excitation of the Sylmar record. The structure-buffer impact was found to be detrimental to the structural response if the structure was not designed to provide inelastic deformation capacity, and the structural response did not improve when the gap was increased to 200-250 mm, the expected maximum displacement capacity of the LRBs used in the building. An alternative isolation system of LRBs and hysteretic dampers was investigated and found to be adequate for resisting near-source motions. A large initial damper stiffness and relatively small buffer stiffness (compared with the total initial stiffness of LRBs) were found to be effective in reducing inter-storey drifts and storey accelerations at floors except for the base and roof of the structure. A disadvantage of such a system is the relatively large base and roof accelerations. The system has relatively large inter-storey drifts and storey accelerations compared with an isolated structure using LRBs only when the structure was subjected to either the 1940 El Centro type ground motions or the Joshua Tree type ground motions with backward directivity effect. Such an isolation system would still enable the structure to respond essentially elastically under the excitation of the Sylmar record even though the isolated structure was designed for a much lower level of ground shaking. As the upper structure of a seismically isolated building is usually designed to respond essentially elastically, the detailing used in the design of a reinforced concrete structure to provide inelastic deformation capacity was generally uncommon and was not fully accounted for in the present study.

The magnitude 8.3 June 23 2001 southern Peru earthquake and tsunami

We present a precis of our reconnaissance trip to the area of the magnitude 8.3 June 23 2001 southern Peru earthquake and tsunami. The trip was undertaken because of the relevance of the event to hazard assessment in New Zealand. It is the best example in nearly 40 years of the maximum-size earthquake that might occur on the Hikurangi subduction zone, an event that is absent from the historical record of New Zealand (since 1840) and therefore of unknown potential in terms of hazard. Despite the great magnitude of this subduction interface earthquake, it produced only "moderately strong" levels of earthquake shaking (peak ground acceleration of 0.3g on alluvium from the one strong motion accelerograph in the earthquake area, and Modified Mercalli Intensity 8 in the epicentral area), and relatively minor ground damage (liquefaction and landslides). It did however produce a large and devastating tsunami. Our comparison of the one accelerograph record and attenuation curves for subduction interface earthquakes shows that the strength of shaking was typical for subduction interface earthquakes. If we apply our observations to New Zealand, they imply that a Hikurangi subduction interface earthquake may be less damaging to built-up areas in the southeastern part of the North Island (e.g. Wellington and Napier/Hastings) than earthquakes on major active faults in the shallow crust. However, the lateral extent of the strongest shaking in a subduction earthquake (300 km for the southern Peru event) and the associated tsunami generation will make the earthquake very significant in the national context.

Perceptible earthquakes in the broad Aegean area

A probabilistic estimate of seismic hazard can be obtained from the spatial distribution, of earthquake sources, their frequency–magnitude distribution and the rate of attenuation of strong ground motion with distance. We calculate the earthquake perceptibility, i.e. the annual probability that a particular level of ground shaking will be generated by earthquakes of particular magnitude, by weighting frequency–magnitude data with the predicted felt area for a given level of ground shaking at a particular magnitude. This provides an earthquake selection criterion that can be used in the anti-seismic design of non-critical structures. We calculate the perceptibility, at a particular value of isoseismal intensity, peak ground acceleration and velocity, as a function of source magnitude and frequency for the broad Aegean area using local attenuation laws. We use frequency–magnitude distributions that were previously obtained by combining short-term catalogue data with tectonic moment rate data for 14 tectonic zones in Greece with sufficient earthquake data, and where contemporary strain rates are available from satellite data. Many of the zones show a ‘characteristic earthquake’ distribution with the most perceptible earthquake equal to the maximum magnitude earthquake, but a relatively flat perceptibility between magnitudes 6 and 7. The maximum perceptible magnitude is in the fastest-deforming region in the middle of the Aegean sea, and tends to be systematically low on the west in comparison to the east of the Aegean sea. The tectonic data strongly constrain the long-term recurrence rates and lead to low error estimates (±0.2) in the most perceptible magnitudes.

Quasi-Static Reversed Cyclic Response of Level and Stepped Cripple Walls

Old residential buildings, such as those built before 1960, were commonly supported on cripple walls, which are walls constructed of short wooden studs between the foundation and first floor framing. For most of these old buildings, the inertial force developed by the horizontal earthquake ground motion must be resisted entirely by the cripple wall and wall-to-foundation connection. Past earthquakes in California have shown that unbraced cripple walls are particularly vulnerable due to insufficient lateral resistance, even for a moderate level of ground shaking. This paper summarizes the results of a test program conducted on level and stepped cripple walls. Specimens with details representative of current construction and retrofit were tested using displacement histories recommended for ordinary and near-fault ground motions. Key parameters of the test program included the height and slope of the cripple wall, gravity load level, stucco finish, loading history, and framing details for stepped cripple wal...

An Approach to Time-Probabilistic Evaluation of Seismically Induced Landslide Hazard

The need for effective strategies for preventing and mitigating damage caused by earthquake-induced landslides has stimulated recent developments of techniques for the assessment of seismic-landslide exposure at a regional scale. However, for a rational risk management, a crucial element is represented by the time horizon of the hazardous events. A new way to incorporate the time factor in seismic-landslide hazard assessment is proposed here. It consists of evaluating the temporal recurrence of seismically induced slope failure conditions inferred from the Newmark's model: First, by adopting Arias Intensity to quantify seismic shaking, well-established methods of seismic hazard assessment are employed to obtain the occurrence probabilities for different levels of seismic shaking in a time interval of interest. Then, some empirical relations, based on the Newmark's model, are employed to evaluate the slope critical acceleration a c for which a prefixed probability exists that seismic shaking would result in landslide triggering. The obtained a c values represent the minimum slope resistance required to keep the probability of seismic-landslide triggering within the prefixed value. Therefore, the space distribution of the calculated a c values can be promptly compared with the actual in situ a c values of specific slopes to estimate whether these slopes have a significant probability of failing under seismic action in the future. An example of this approach, applied to an area in southern Italy (Daunia region), shows that the introduction of the time factor significantly modifies the representation of the spatial hazard and allows evaluation of the relevance of seismicity as a landslide triggering agent.

Dynamic characteristics of a base isolated building from ambient vibration measurements and low level earthquake shaking

Ambient vibration tests were conducted on a base-isolated apartment building in Takamatsu, Japan, to determine the mode shapes and the associated natural frequencies and damping ratios at very low levels of excitation. The latest developments in signal analysis for modal decomposition are used to analyze the ambient response data. A finite element model of the building and isolators was calibrated and refined using the experimental results from the ambient vibration tests. This model was then used to simulate the recorded response of the building under excitation from a small earthquake. The finite element model, calibrated by ambient vibration data and the low level of earthquake shaking, provides the starting point for modelling the non-linear response of the building when subjected to strong shaking.

Response spectrum predictions for potential near-field and far-field earthquakes affecting Hong Kong: soil sites

This paper considers the modelling of design-level earthquake response spectra for soil sites in Hong Kong. It forms part of a series of connected studies aimed at quantifying the detailed characteristics of seismic activity and design ground shaking levels in Hong Kong and its surrounding region. This series of papers should appeal to a broad international readership interested in adopting a methodology to determine seismic demand for infrastructure in megacities located within a low or moderate seismic region. The peak velocity and displacement demands (soil RSV max and soil RSD max, respectively) have been obtained from soil response analyses for numerous representative soil column models. The comparison of the soil RSV max between individual soil columns displays interesting similarities for a given earthquake scenario. A unique upper bound RSV max value has been identified for each probability of exceedence (PE). The predicted soil RSV max was found to be relatively insensitive to the lengthening of return period. Another significant trend is the excellent linear correlation between the peak displacement demand (soil RSD max) and the site natural period ( T s). A simple relationship has accordingly been developed to determine the soil RSD max from the given soil RSV max and T s. Maximum soil amplification factors (spectral ratios) in the order of 5–6 have been observed in the present study, for Hong Kong soil sites resonating under the action of bedrock shaking induced by distant, large magnitude earthquake events associated with a range of PE. Previous studies have grossly underestimated this factor, due to inaccurate representation of the bedrock motions generated by far-field earthquakes and due to underestimation of the soil-rock impedance contrast. Furthermore, codified estimates of site amplification may significantly underestimate the effect of resonance, due to distortion introduced by various forms of idealisation and normalisation when dealing with the soil and bedrock response spectra.

SEISMIC PERFORMANCE EVALUATION CHARTS FOR GRAVITY TYPE QUAY WALLS

More than two hundred cases of effective stress analyses with variation of seismic coefficients and liquefaction resistance were conducted. Among the parameters considered in this study, the most sensitive parameter affecting the wall displacement under a prescribed level of shaking is the SPT N-value of subsoil below and behind the wall. With the results of parametric calculations, a simple procedure and charts are proposed to evaluate the order-of-magnitude displacement of a quay wall. It demonstrated the capability to evaluate a wide range of displacements, ranging from the displacement in the order of one-tenths of meters to those with one order higher.

Displaced Rocks, Strong Motion, and the Mechanics of Shallow Faulting Associated with the 1999 Hector Mine, California, Earthquake

The paucity of strong-motion stations near the 1999 Hector Mine earthquake makes it impossible to make instrumental studies of key questions about near-fault strong-motion patterns associated with this event. However, observations of displaced rocks allow a qualitative investigation of these problems. By observing the slope of the desert surface and the frictional coefficient between these rocks and the desert surface, we estimate the minimum horizontal acceleration needed to displace the rocks. Combining this information with observations of how many rocks were displaced in different areas near the fault, we infer the level of shaking. Given current empirical shaking attenuation relationships, the number of rocks that moved is slightly lower than expected; this implies that slightly lower than expected shaking occurred during the Hector Mine earthquake. Perhaps more importantly, stretches of the fault with 4 m of total displacement at the surface displaced few nearby rocks on 15° slopes, suggesting that the horizontal accelerations were below 0.2 g within meters of the fault scarp. This low level of shaking suggests that the shallow parts of this rupture did not produce strong accelerations. Finally, we did not observe an increased incidence of displaced rocks along the fault zone itself. This suggests that, despite observations of fault-zone-trapped waves generated by aftershocks of the Hector Mine earthquake, such waves were not an important factor in controlling peak ground acceleration during the mainshock.

LIQUEFACTION AND PILED FOUNDATIONS: SOME ISSUES

Selected case histories recording the behaviour of piled foundations in lateral-spreading fields are reviewed. From these observations and from laboratory experiments in the centrifuge and on the shaking table, it is clear that the resistance of liquefied soil is very small and that the critical points for a pile are at the bottom as well as near the top of the liquefied layer. It is also apparent that liquefaction does not-occur until a significant threshold level of shaking is exceeded, and that even then it does not occur instantaneously. Thus damaging motions can be felt by the pile and transmitted to the superstructure before liquefaction and lateral spreading occurs. There is a critical period early in the shaking when the soil has softened enough for ground motion to be amplified but is still stiff enough to induce large bending moments in the pile, near the top of the liquefiable layer. Liquefaction is certainly not a dependable base-isolation mechanism. A controversial issue concerns the continuity or localisation of displacement within the liquefied layer. There is evidence that, in the majority of cases, displacement within the liquefied layer is continuous with depth; although when a sufficiently impermeable layer overlies the liquefiable one, a layer of free water can accumulate and localise displacement. Another old controversy, which now seems to be resolved, concerns the generation of passive earth pressures in non-liquefiable surface layers. There is clear field and laboratory evidence for the development of the passive state in superficial layers. For use in everyrday design, two simple methods of analysis have recently emerged. They are the earth pressure method and the seismic deformation method. They have been calibrated against the Kobe data and appear to work well in the few cases where they have been checked on other soils. It remains for them to be verified against a broader range of soils and for further soil-spring models.

Anomalous Concentrations of Seismically Triggered Rock Falls in Pacoima Canyon: Are They Caused by Highly Susceptible Slopes or Local Amplification of Seismic Shaking?

Anomalously high concentrations of rock falls were triggered in Pacoima Canyon (Los Angeles, California) during the 1994 Northridge earthquake. Similar concentrations were also documented from the 1971 San Fernando earthquake. Using an engineering rock-mass classification that evaluates the susceptibility of rock slopes to seismic failure based on the fracture properties of a rock mass (in terms of a numerical “ Q -value” that describes rock quality), the rock slopes in Pacoima Canyon were compared with rock slopes in surrounding areas where topography and lithology are similar, but rock-fall concentrations from the earthquakes were much lower. A statistical comparison of Q -values from five sites surrounding Pacoima Canyon indicates that seismic susceptibilities are similar to those within Pacoima Canyon; differences in the characteristics of rock slopes between these sites are not sufficient to account for the relatively high concentrations of rock falls within Pacoima Canyon as compared to low concentrations elsewhere. By eliminating susceptibility differences as a cause, the most likely explanation for the differences in rock-fall concentrations is anomalously high shaking levels in Pacoima Canyon, possibly resulting from topographic amplification within the canyon. Manuscript received 21 May 2001.

Probabilistic seismic hazard assessment of the Canterbury region, New Zealand

We present the main results of a probabilistic seismic hazard assessment of the Canterbury region recently completed for Environment Canterbury (formerly Canterbury Regional Council). We use the distribution of active faults and the historical record of earthquakes to estimate the levels of earthquake shaking (peak ground acceleration and response spectral accelerations) that can be expected across the Canterbury region with return periods of 150, 475 and 1000 years. The strongest shaking (e.g. 475 year peak ground accelerations of 0.7g or more) can be expected in the west and north to northwest of the Canterbury region, where the greatest concentrations of known active faults and historical seismicity are located. Site-specific analyses of eight towns and cities selected by Environment Canterbury show that Arthur's Pass and Kaikoura are located within these zones of high hazard. In contrast, the centres studied in the Canterbury Plains (Rangiora, Kaiapoi, Christchurch, Ashburton, Temuka and Timaru) are generally located away from the zones of highest hazard. The study represents the first application of recently-developed methods in probabilistic seismic hazard at a regional scale in New Zealand.

The New Madrid Seismic Zone: Capturing Variability in Seismic Hazard Analyses

Recently, concern has been raised about variability in input parameters affecting seismic hazard results (Newman et al., 1999, 2000a, 2000b, 2001). Uncertainty in seismic hazard calculations for the eastern U.S. (EUS) has been a major concern for the last two decades (EPRI, 1986; SSHAC, 1997). The use of a logic tree to capture knowledge-based uncertainty in seismic hazard calculations has developed over this rime period (Coppersmith and Youngs, 1986; NRC, 1988; Reiter, 1990; Cramer et al., 1996a). A recent reassessment of the current state of knowledge for the New Madrid seismic zone (EOS, 2000) has led to updating of the seismic hazard assessment in the central U.S. That updated seismic hazard assessment is used here to demonstrate how variability should be captured in a seismic hazard analysis. This presentation starts with a brief introduction to seismic hazard analysis, continues with a short discussion of how variability is handled and represented in an uncertainty analysis, and finally gives an example of an uncertainty analysis and its value. Although they occur infrequently, future earthquakes in the central and eastern U.S. (CEUS) are certain to have significant economic and social impact. In order to prepare for such events, there must be an understanding of the anticipated level of earthquake ground shaking. This information is important in public policy and private risk assessment and in decision-making. Part of the seismic hazard analysis process is to account scientifically for both what is known and what is not known about earthquake hazards in a region and to develop a best estimate for anticipated future earthquake ground motions. Because our knowledge about earthquakes is incomplete, it is vital that a scientific consensus be built with the best available information on which to base seismic hazard estimates. One possible approach to seismic …