Long-period Ground Motions Research Articles

The Role of Long-Period Ground Motions on Magnitude and Damage of Volcanic Earthquakes on Mt. Etna, Italy

On October 2002, a seismic swarm occurred on Mt. Etna. One of the strongest events caused severe damage, up to a European Macroseismic Scale inten- sity of VIII that contrasts with its local magnitude of 4.4. The occurrence of significant damage at such a small magnitude is repeatedly observed in the area and is tradition- ally attributed to shallow source. Recorded strong-motion accelerograms and broad- band seismograms demonstrate that there is one more cause for the severe damage, that is, an anomalously strong low-frequency (0:1 <f< 1 Hz) radiation deviating from the conventional Brune (1970) spectral scaling. Therefore, these earthquakes cause large ground displacements and long (≈20 sec) durations of shaking. The integration of digital accelerograms yields a maximum peak ground displacement as large as 1.8 cm at a distance of 18 km. Based on the sharp local attenuation of ground motion in the study area, we infer that peak ground displacements near the epicenters did exceed 10 cm. The occurrence of large displacements caused selective damage to medium-rise (≥3 stories) reinforced concrete buildings and elements like church facades. The frequency cutoff below 1.25 Hz in the Wood-Anderson response attenuates the peak-to-peak amplitudes used to assess local magnitudes. Therefore, ML values are not representative of the real strength of volcanic earthquakes. Because a prompt magnitude (and damage potential) assessment is crucial for civil protection actions, a procedure is proposed which, in near-real time, can be successful in identifying po- tentially damaging earthquakes of Mt. Etna through the computation of pseudove- locity response spectra. The procedure provides a magnitude value that is derived on a statistical basis from the Housner (1952) spectral intensity computed in the low-frequency band. This parameter is a suitable near-real-time indicator of large earthquake-induced building shaking and could also be applied for a preliminary es- timate of the epicentral macroseismic intensity.

Development of Long-period Ground Motions from the Nankai Trough, Japan, Earthquakes: Observations and Computer Simulation of the 1944 Tonankai (Mw 8.1) and the 2004 SE Off-Kii Peninsula (Mw 7.4) Earthquakes

Strong ground motions recorded in central Tokyo during the 1944 Tonankai Mw8.1 earthquake occurring in the Nankai Trough demonstrate significant developments of very large (>10 cm) and prolonged (>10 min) shaking of long-period (T > 10–12 s) ground motions in the basin of Tokyo located over 400 km from the epicenter. In order to understand the process by which such long-period ground motions developed in central Tokyo and to mitigate possible future disasters arising from large earthquakes in the Nankai Trough, we analyzed waveform data from a dense nation wide strong-motion network (K-NET and KiK-net) deployed across Japan for the recent SE Off-Kii Peninsula (Mw 7.4) earthquake of 5 September 2004 that occurred in the Nankai Trough. The observational data and a corresponding computer simulation for the earthquake clearly demonstrate that such long-period ground motion is primarily developed as the wave propagating along the Nankai Trough due to the amplification and directional guidance of long-period surface waves within a thick sedimentary layer overlaid upon the shallowly descending Philippine Sea Plate below the Japanese Island. Then the significant resonance of the seismic waves within the thick cover of sedimentary rocks of the Kanto Basin developed large and prolonged long-period motions in the center of Tokyo. The simulation results and observed seismograms are in good agreement in terms of the main features of the long-period ground motions. Accordingly, we consider that the simulation model is capable of predicting the long-period ground motions that are expected to occur during future Nankai Trough M 8 earthquakes.

Prediction of long-period ground motions from huge subduction earthquakes in Osaka, Japan

There is a high possibility of reoccurrence of the Tonankai and Nankai earthquakes along the Nankai Trough in Japan. It is very important to predict the long-period ground motions from the next Tonankai and Nankai earthquakes with moment magnitudes of 8.1 and 8.4, respectively, to mitigate their disastrous effects. In this study, long-period (>2.5 s) ground motions were predicted using an earthquake scenario proposed by the Headquarters for Earthquake Research Promotion in Japan. The calculations were performed using a fourth-order finite difference method with a variable spacing staggered-grid in the frequency range 0.05–0.4 Hz. The attenuation characteristics (Q) in the finite difference simulations were assumed to be proportional to frequency (f) and S-wave velocity (Vs) represented by Q = f · Vs / 2. Such optimum attenuation characteristic for the sedimentary layers in the Osaka basin was obtained empirically by comparing the observed motions during the actual M5.5 event with the modeling results. We used the velocity structure model of the Osaka basin consisting of three sedimentary layers on bedrock. The characteristics of the predicted long-period ground motions from the next Tonankai and Nankai earthquakes depend significantly on the complex thickness distribution of the sediments inside the basin. The duration of the predicted long-period ground motions in the city of Osaka is more than 4 min, and the largest peak ground velocities (PGVs) exceed 80 cm/s. The predominant period is 5 to 6 s. These preliminary results indicate the possibility of earthquake damage because of future subduction earthquakes in large-scale constructions such as tall buildings, long-span bridges, and oil storage tanks in the Osaka area.

Validation of 3-D basin structure models for long-period ground motion simulation in the Osaka basin, western Japan

We studied the applicability of two types of existing three-dimensional (3-D) basin velocity struc- ture models of the Osaka basin, western Japan for long-period ground motion simulations. We synthe- sized long-period (3-20 s) ground motions in the Osaka basin during a M6.5 earthquake that occurred near the hypothetical Tonankai earthquake source area, approximately 200 km from Osaka. The simu- lations were performed using a 3-D finite-difference method with nonuniform staggered grids using the two basin velocity structure models. To study the ground motion characteristics inside the basin, we evaluated the wave field inside the basin using the transfer functions derived from the synthetics at the basin and a reference rock site outside the basin. The synthetic waveforms atthe basin site were obtained by a convolution of the calculated transfer function and the observed waveform at the reference rock site. First, we estimated the appropriate Q values for the sediment layers. Assuming that the Q value depends on the S wave velocity VS and period T, it was set to Q=(1/3VS)(T0/T) where VS is in m/s and the reference period T0 is 3.0 s. Second, we compared the synthetics and the observations using waveforms and pseudovelocity response spectra, together with a comparison of the velocity structures of the two basin models. We also introduced a goodness-of-fit factor to the pseudovelocity response spectra as an objective index. The synthetics of both the models reproduced the observations reasonably well at most of the stations in the central part the basin. At some stations, however, especially where the bedrock depth varies sharply, there were noticeable discrepancies in the simulation results of the models, and the synthetics did not accurately reproduce the observation. Our results indicate that the superiority of one model over the other cannot be determined and that an improve- ment in the basin velocity structure models based on simulation studies is required, especially along the basin edges. We also conclude that our transfer function method can be used to examine the applica- bility of the basin velocity structure models for long- period ground motion simulations.

Model for Basin Effects on Long-Period Response Spectra in Southern California

We propose a model for the effect of sedimentary basin depth on long-period response spectra. The model is based on the analysis of 3-D numerical simulations (finite element and finite difference) of long-period (2–10 s) ground motions for a suite of sixty scenario earthquakes (Mw 6.3 to Mw 7.1) within the Los Angeles basin region. We find depth to the 1.5 km/s S-wave velocity isosurface to be a suitable predictor variable, and also present alternative versions of the model based on depths to the 1.0 and 2.5 km/s isosurfaces. The resulting mean basin-depth effect is period dependent, and both smoother (as a function of period and depth) and higher in amplitude than predictions from local 1-D models. The main requirement for the use of the results in construction of attenuation relationships is determining the extent to which the basin effect, as defined and quantified in this study, is already accounted for implicitly in existing attenuation relationships, through (1) departures of the average “rock” site from our idealized reference model, and (2) correlation of basin depth with other predictor variables (such as Vs30).

Finite-element simulations of long-period ground motions: Japanese subduction-zone earthquakes and the 1906 San Francisco earthquake

Large earthquakes at shallow depths commonly excite long-period ground motions in distant sedimentary basins, thereby inflicting damage upon large-scale structures. For example, the 2003 Tokachi-oki earthquake, Japan, damaged oil tanks in the Yufutsu Basin, located 250 km from the epicenter. Similar long-range effects were also observed during the 2004 earthquake off Kii Peninsula, Japan. In this study, we present the results of simulations of these earthquakes undertaken using the finite element method (FEM) with a voxel mesh. In addition, to examine whether the 1906 San Francisco earthquake excited long-period ground motions in the Los Angeles-area basins, we performed long-period ground motion simulations of most of the California region. The FEM simulations confirmed the importance of path effects for the development of long-period ground motions.

Prediction of ground motion in the Osaka sedimentary basin associated with the hypothetical Nankai earthquake

We studied the long-period ground motions in the Osaka sedimentary basin, Japan, which contains a 1- to 3-km thickness of sediments and is the site of many buildings or construction structures with long-natural period. We simulated the broadband ground motions likely to be produced by the hypothetical Nankai earthquake: the earthquake expected to give rise to the most severe long-period ground motion within the basin. For the simulation, we constructed multiscale heterogeneous source models based on the Central Disaster Management Council of Japan (CDMC) source model and adopted a hybrid computation method in which long-period motion and short-period motion are computed using a 3-D finite difference method and the stochastic Green’s function method, respectively. In computing long-period motions, we used a 3-D structure model of the crust and the Osaka sedimentary basin. The ground motions are estimated to have peak velocities of 50–90 cm/s, prolonged durations exceeding 300 s, and long predominant periods of 5–10 s in the area with great thickness of sediments. The predominant periods are in agreement with an approximate evaluation by 4 H/V s where H and V s are the thickness of the sediment and the average S wave velocity, respectively.

Basin and crustal velocity structure models for the simulation of strong ground motions in the Kinki area, Japan

We constructed a prototype of the basin and crustal structure model for the Kinki area, southwest of Japan, for the simulation of strong ground motions of hypothetical crustal and subduction earthquakes. We collected results of the deep seismic velocity profiles obtained by the reflection experiments and seismic imaging results, which were conducted in the Kinki area. The obtained profiles give underground velocity structures of the crust, from the surface to the subducting slab. We also gather the basin velocity structure information of the Osaka, Kyoto, Nara, and Ohmi basins. To examine the applicability of the constructed velocity structure model to the ground motion simulation, we simulated waveforms of an intermediate size event occurred near the source area of the hypothetical subduction earthquakes. Simulated ground motions using the basin and crustal velocity structure model are fairly well reproducing the observations at most of stations, and the constructed basin and crustal velocity structure model is applicable for the long-period ground motion simulations.

A seismological overview of long-period ground motion

Long-period ground motion has become an increasingly important consideration because of the recent rapid increase in the number of large-scale structures, such as high-rise buildings and oil storage tanks. Large subduction-zone earthquakes and moderate to large crustal earthquakes can generate far-source long-period ground motions in distant sedimentary basins with the help of path effects. Near-fault long-period ground motions are generated, for the most part, by the source effects of forward rupture directivity. Far-source long-period ground motions consist primarily of surface waves with longer durations than near-fault long-period ground motions. They were first recognized in the seismograms of the 1968 Tokachi-oki and 1966 Parkfield earthquakes, and their identification has been applied to the 1964 Niigata earthquake and earlier earthquakes. Even if there is no seismogram, we can identify far-source long-period ground motions through the investigation of tank damage by liquid sloshing.

3D crustal structure and long-period ground motions from a M9.0 megathrust earthquake in the Pacific Northwest region

We have developed a community velocity model for the Pacific Northwest region from northern California to southern Canada and carried out the first 3D simulation of a Mw 9.0 megathrust earthquake rupturing along the Cascadia subduction zone using a parallel supercomputer. A long-period (<0.5 Hz) source model was designed by mapping the inversion results for the December 26, 2004 Sumatra–Andaman earthquake (Han et al., Science 313(5787):658–662, 2006) onto the Cascadia subduction zone. Representative peak ground velocities for the metropolitan centers of the region include 42 cm/s in the Seattle area and 8–20 cm/s in the Tacoma, Olympia, Vancouver, and Portland areas. Combined with an extended duration of the shaking up to 5 min, these long-period ground motions may inflict significant damage on the built environment, in particular on the highrises in downtown Seattle.

矩形断面容器におけるスロッシング対策案の検討

he sloshing phenomenon might be caused by long-period ground motion. As a result of it, the storage liquid might overflow. The pool of the nuclear waste storage overflowed due to the Niigata Chuetsuoki Earthquake is the recent case. In this paper, shaking experimentation was conducted by setting up small tank of rectangular section on shaking table to make this cause clear. In addition, the effect of setting the net in small tank inside as one of sloshing measurement is explained.

断層破壊過程の複雑さが強震動予測結果に及ぼす影響とその支配的パラメータの抽出

The procedure for source modeling according to a characterized source model has been proposed and established in prevenient researches on the estimation of strong ground motions from scenario earthquakes along active faults. In recent researches, such procedure is also applied to the strong ground motion prediction for some great subduction earthquakes. In these cases, it seems that short-period motions are underestimated while long-period ground motions explain the observed records well. We examine the effects of complexity of fault rupture process on strong ground motions in period range form 5 to 10 s by handling source parameters of the 2003 Tokachi-Oki earthquake. For that purpose, we referred to the source model obtained by inversion analysis of near-field strong motion records in the antecedent research. First, we have made several simplified models from original source model. In the models, we gradually simplified the source parameters, such as slip amount, rupture time, rake angle, and the form of slip velocity time function of fault elements. Contribution of each source parameter to the waveform complexity has been evaluated by comparing spectral levels of synthetic waveforms from different source models in three frequency ranges and by comparing synthetic waveforms themselves. As a result, the complexity of rupture propagation is most important to correctly simulate ground motions in the period of several seconds for M 8 earthquake. We have also examined relation between the rupture propagation complexity and the slip distribution. The result shows that acceleration of rupture propagation is seen in the areas where either slip or spatial gradient of slip is large.

103 エレベーターの新しい地震対応技術

The seismic-proof design for the elevator system is important subject to maintain vertical transportation in buildings after an earthquake. If an earthquake is detected immediately, elevators can switch their service to proper earthquake emergency operations and, as such, prevent any trouble. Therefore, in this paper, seismic detector levels are evaluated numerically. Three new seismic-proof systems are also introduced. One of the systems is the emergency operation with the earthquake early warning system. Second one is detection of long-period ground motion and its emergency operation. Final one is the automatic diagnosis and recovery system after an earthquake.

A RESPONSE SPECTRUM METHOD FOR PREDICTING SLOSHING AND SEISMIC RESPONSE OF A FLOATING ROOF IN A CYLINDRICAL LIQUID STORAGE TANK

A response spectrum method is proposed to predict the sloshing and dynamic response of a floating roof in a cylindrical liquid storage tank subjected to long-period ground motion. The liquid is assumed to be inviscid, incompressible, and irrotational, while the floating roof is considered as an orthotropic elastic plate of variable thickness. The dynamic interaction between the liquid and the floating roof is taken into account exactly within the framework of linear potential theory. The analysis is based on expanding the response of the floating roof into free vibration modes in liquid to derive the diagonalized equations of motion for the coupled liquid-floating roof system. The modal analysis based on the response spectrum is then carried out to predict the sloshing and dynamic response of the floating roof. Numerical results are presented to illustrate the applicability of the proposed method

Preface to the 2006 Pingtung Earthquake Doublet Special Issue

On 26 December 2006, two closely linked earthquakes, both ML 7.0, occurred only 8 minutes apart at 12:26:21 and 12:34:15 UT, respectively, in southwestern offshore of Taiwan near Pingtung. These two earthquakes were referred to as the Pingtung Earthquake Doublet that is unique not only because of being an earthquake doublet, but also both events were the largest in southwestern Taiwan during the past one hundred years. The occurrence of this doublet was in a region, where the seismic activity has been relatively low. According to the Central Weather Bureau (CWB) catalog, the epicenter of the first event is located at 21.69 N and 120.56 E with a focal depth 44 km and a magnitude of ML = 7.0 (Mw = 7.0 Global CMT), the second earthquake was at 21.97 N and 120.42 E, about 36 km to the northnortheast of the first event, with a magnitude of ML = 7.0 (Mw = 6.9 Global CMT) and a focal depth of 50 km. This earthquake doublet caused 44 injuries, including 2 fatal ones, 3 building collapses, and a massive failure of submarine communication cables, resulting in a significant economic loss. In addition, the Taipower’s Nuclear Power Plant No. 3 (NPP3), which is within about 50 km from the epicenters of the earthquake doublet, registered the largest motions ever since the strong-motion recording commenced at the plant site. As a result, the Unit 2 of NPP3 was shut down while Unit 1 remained operatal at the time of the doublet event. The occurrence of this earthquake doublet has caused a debate on the possible association to an active fault, and its linkage to the subducting slab of Manila trench. The focal mechanisms determined from Broadband Array in Taiwan for Seismology (BATS) were a normal faulting for the first, and a strike-slip faulting for the second event. The associated rupture planes of the earthquake doublet were difficult to determine due to the sparse distribution of the aftershocks for the first one. The aftershock distribution from the CWB near the hypocentral area of the second one suggests a west-dipping northwest-southeast striking ruptured plane. Tectonically, this earthquake doublet gives the insight toward understanding of the seismic activity in southwestern Taiwan, and thus, brings special attention to the potential hazard from large earthquakes in southern Taiwan. In view of the characteristics of the earthquake doublet, in this Special Issue, we have compiled valuable data observed from this earthquake doublet and studies investigating earthquake occurrence and rupture characteristics of this earthquake doublet. We believe that this Special Issue should be a useful documentation to the Pintung earthquake doublet, and will be beneficial to the hazard mitigation of the future large earthquakes associated with the southwestern Taiwan tectonics. This Pingtung Earthquake Doublet Special Issue consists of 16 regular articles and 2 notes. It began with three articles on the discussion of the initial rupture of the earthquake by Haung et al. (2008a), the fault rupture plane determination and spatial slip distribution analysis from the regional strong motion and BATS waveform data by Lee et al. (2008) and Yen et al. (2008) to obtain the geometry of fault ruptures and to discuss the interaction of the earthquake doublet from the spatial slip distributions based on teleseismic data. Chen et al. (2008d) used the teleseismic data to refine the source depths of this earthquake doublet. Furthermore, Lin et al. (2008) studied the possible static triggering of earthquake doubles in convergent zones of Taiwan. The valuable strong motion data from the CWB’s Taiwan Strong-Motion Instrumentation Program (TSMIP) stations for this earthquake doublet was compiled by four articles. The most comprehensive one is by Wu et al. (2008a), giving the data processing procedures for the efficient use of the data for other researchers, and a comparison of ground motions recorded by multiple accelerographs at a common site in Taipei, and attenuation of the horizontal ground motions. Wen et al. (2008) compiled the damage features and strong motion records, especially near the Taipower’s Nuclear Power Plant No. 3, to give the seismic hazard assessment for southwestern Taiwan. Chen et al. (2008b) gave special attention to the long-period ground motion observations along paths of the earthquake doublet traversing the Central Range, and the Longitudinal Valley, respectively. Lee and Tsai (2008), furthermore, provided the near site structure for mapping average shear-wave velocity of the upper 30 meters of soil profile (Vs30) in Taiwan. In addition to seismic data, GPS observations and analysis associated with this earthquake doublet were also carried out by Chen et al. (2008a). For offshore large earthquakes, several articles address their corresponding tsunami potential and the possible association of the earthquake doublet with the offshore tectonic structure. Chen et al. (2008c) evaluated the earthquake probabilities and energy characteristics in southwestern offshore Taiwan for the slow tsunami earthquake, and Wu et al.

Long-Period Ground Motion Observations along Two Linear Profiles from the 26 December 2006 Pingtung Offshore Earthquakes

Long-Period Ground Motion Observations along Two Linear Profiles from the 26 December 2006 Pingtung Offshore Earthquakes

EXPERIMENTAL INVESTIGATION ON DEFORMATION CAPACITY OF BEAM-TO-COLUMN CONNECTIONS IN EARLY HIGHRISE BUILDINGS BY FULLSCALE TESTS

This paper presents results of fullscale tests conducted to evaluate deformation capacity and failure mode of welded beam-to-column connections adopted in moment frames for early highrise buildings around 1970s. Test specimens are designed and fabricated to reproduce the moment connections at that time according to the welding details and steel work procedures. Loading tests are conducted by cyclic loading protocol to simulate the response of frames subjected to long-period ground motions. The obtained capacity of specimens evaluated by cumulative plastic rotation satisfied deformation demand predicted by numerical response analysis.

Long-period ground motions from the 2003 Tokachi-oki earthquake

We study characteristics of long-period ground motions from the 2003 Tokachi-oki earthquake (Mj 8.0), a large interplate earthquake, based on spatial distribution maps and attenuation relationships for four kinds of peak ground velocity (PGV) value. The first kind (PGV(WB)) is obtained from a maximal value of vector sum of the three-component, wide-band velocity seismograms, and the other three kinds (PGV(BP10), PGV(BP20), and PGV(BP30)) are obtained from a maximal value of vector sum of the three-component, narrow band-pass filtered velocity seismograms (the central periods are 10, 20, and 30 s). The spatial distribution maps for all kinds of PGV value show azimuth dependence; the PGV values in Hokkaido, northern side of the epicenter are larger than those in Tohoku, southwestern side of the epicenter, when compared at a comparable distance. We find that the features result from the radiation pattern of long-period surface waves, that is, the source effect. The attenuation relationships show the following trends: The PGV(WB) values are larger than the sum of the PGV(BP10), PGV(BP20), and PGV(BP30) at distances (D) less than 200 km, while the PGV(WB) values are comparable to the sum of the PGV(BP20) and PGV(BP30) at D > 200 km. This indicates that the PGV(WB) values at D 200 km. The basin site effects generate a patchy pattern in the spatial distribution maps and a large scattering in the attenuation relationships for the PGV(WB) and PGV(BP10) values. Finally, we conclude that the PGV(WB) values from the 2003 Tokachi-oki earthquake are controlled by the radiation pattern of long-period S and surface waves and various basin site effects.

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 (Mw 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.

Hazard-consistent response spectra in the Region of Murcia (Southeast Spain): comparison to earthquake-resistant provisions

Hazard-consistent ground-motion characterisations of three representative sites located in the Region of Murcia (southeast Spain) are presented. This is the area where the last three damaging events in Spain occurred and there is a significant amount of data for comparing them with seismic hazard estimates and earthquake-resistant provisions. Results of a probabilistic seismic hazard analysis are used to derive uniform hazard spectra (UHS) for the 475-year return period, on rock and soil conditions. Hazard deaggregation shows that the largest hazard contributions are due to small, local events for short-period target motions and to moderate, more distant events for long-period target motions. For each target motion and site considered, the associated specific response spectra (SRS) are obtained. It is shown that the combination of two SRS, for short- and long-period ground motions respectively, provides a good approximation to the UHS at each site. The UHS are compared to design response spectra contained in current Spanish and European seismic codes for the 475-year return period. For the three sites analysed, only the Eurocode 8 (EC8) type 2 spectrum captures the basic shape of the UHS (and not the EC8 type 1, as could be expected a priori). An alternative response spectrum, anchored at short- and long-period accelerations, is tested, providing a close match to the UHS spectra at the three sites. Results underline the important contribution of the frequent, low-to-moderate earthquakes that characterize the seismicity of this area to seismic hazard (at the 475-year return period).