Top PDF A Study of High Frequency Strong Ground Motion from the San Fernando Earthquake

motion generally involved only correlations between earthquake magnitude and recorded peak ground motion values, and did not consider details of the rupture mechanism and the geology of [r]

The target area of this study is the Kinki in Western Japan and adjacent areas (see Fig. 1). Many large cities are located in this area, including Osaka, Kobe, Kyoto, and Nagoya. The Kinki area has a high seismic hazard potential rating. Based on the long-term evaluation of earthquake occur- rence, the Headquarters for Earthquake Research Promo- tion (HERP) of the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), Japan, reported that the occurrence potentials of the next Nankai (off Shikoku) and Tonankai (off Kii Peninsula) earthquakes are high: about 60–70% within the next 30 years starting from 2009 (HERP, 2009). The source regions of these earthquakes, and of those of other subduction zone earthquakes, are mostly lo- cated in the offshore area, under an oceanic water layer of 1–3 km depth (Fig. 1).

The kinematic heterogeneous slip histories on the source fault of this megathrust event were estimated in space and in time by inversion analyses of teleseismic data (e.g., Ammon et al., 2011; Hayes, 2011; Ide et al., 2011; Shao et al., 2011; Yagi and Fukahata, 2011), strong motion data (e.g., Suzuki et al., 2011; Yoshida et al., 2011a), both teleseis- mic and strong motion data (e.g., Yoshida et al., 2011b), and combined datasets of teleseismic, strong motion, and geodetic data (e.g., Koketsu et al., 2011). However, those studies used the seismic waves at strong motion stations in the frequency range lower than 0.1 or 0.125 Hz. It is not easy for those source models, which are constrained by the lower frequency data, to reproduce the observed broadband ground motions. In order to account for the observed strong ground motions of frequencies higher than 0.1 Hz, which are usually related to seismic damages on building and civil structures, constraints on the source process by higher fre- quency data are indispensable. It is useful for such an anal- ysis to use the records of small events occurring close to the target event as empirical Green’s functions.

for Japan (Zhao et al., 2006) showed acceptable results for this event, they have been developed without using any data for earthquakes in this magnitude range with such large amplitudes at long periods. Considering that the closest seis- mic records were onshore at ∼ 75 km from the epicenter, the high-frequency ground motions were already attenuated when reaching the coastline of Japan. Psimoulis et al. (2014) showed that the 5% damped pseudospectral acceler- ation (PSA) at 3 s retrieved with GPS was the same as that retrieved with the accelerometric network, which is a further indication of the capability of GPS data for such events. Be- cause the study of Psimoulis et al. (2014) was based on 1 Hz, it was unclear how much of PGV could have been captured by the GNSS Earth Observation Network System (GEO- NET) running at a higher sampling rate. In the present study, we investigate whether high-rate GPS records are able to, and how reliably they can, quantify “true” broadband PGV. We also determine what sampling rate is optimal to capture the widest range of signal, while not recording sensor noise.

As mentioned in Section 2, arrival time of main phases at southern stations on the hanging wall are significantly later than expected arrival time of direct S -wave from the hypocenter,. This is because contribution of asperity (c) is most dominant in waveform of the south stations and as- perity (a) hardly contributes to waveform of those stations. Kamae et al. (2005) also obtained a small asperity at the southwest of the epicenter by the empirical Green’s func- tion method. They concluded that a small asperity was es- sential to reproduce high-frequency ground motions with large peak acceleration recorded at NIG021 and NIG022. These results suggest that time delay of remarkable pulses observed at the southern stations is owing to locations of asperity which contribute to the waveforms.

distributed over a duration related to the earthquake magnitude and to distance from the source (Boore, Simulation of Ground Motion Using the Stochastic Method, 2003). This method of simulating ground motions often goes by the name “the stochastic method.” (McGuire, 2004). It is particularly useful for simulating the higher-frequency ground motions of most interest to engineers. It is widely used to predict ground motions for regions of the world in which recordings of motion from damaging earthquakes are not available (McGuire, 2004). This simple method has been successful in matching a variety of ground-motion measures for earthquakes with seismic moments spanning more than 12 orders of magnitude. One of the essential characteristics of the method is it distills what is known about the various factors affecting ground motions (source, path, and site) into simple functional forms that can be used to predict ground motions. Stochastic methods (Boore, Simulation of Ground Motion Using the Stochastic Method, 2003) estimate ground motions during an earthquake based on physical properties of the energy release and the travel path of seismic waves. From the characteristics of the process in a time, an estimate can be made of spectral response, peak motion parameters, or any other desired measure (including nonlinear response).

Our analysis of GPS in this study is restricted to the KAZE data. Nevertheless, we find a lot on the 2003 Tokachi-oki earthquake. The time difference of about 20 sec in Fig. 3 is understood to be partly due to our simplified parameters on the faulting process to calculate the synthetic seismograms and not the timing error of the GPS. It is common in na- ture that there is an initial minor breakage with some build- up time necessary to grow into a large failure, especially for great, shallow earthquakes (Koyama, 1997). The simplifica- tion of the faulting model would not generate such an initial minor breakage and the actual faulting process of the 2003 Tokachi-oki earthquake has been characterized by a small amount of seismic moment in the first 15 to 20 seconds, as the YK Model predicted. This also suggests that the simpli- fied fault would also be responsible to some extent for the de- ficiency in the synthetic amplitude. It is possible to assume much more seismic moment release of the second asperity than that in this analysis, while the net seismic moment is the same. There is also a GPS station deployed by the GSI in Erimo, which is about 10 km away from KAZE station. The 1-sec sampling records retrieved from Erimo of the GSI show two pulses, but they are not so clear as at KAZE. Since KAZE observation is the closest to the source region, the data is essential to constrain the detail faulting process of the 2003 Tokachi-oki earthquake, not only on its geometry but also displacement distribution.

Accelerometers have been installed at the following four sites along a straight (west to east) profile in the Kathmandu Valley: KTP (Kirtipur Municipality Office, Kirtipur), TVU (Central Department of Geology, Tribhuvan University, Kirtipur), PTN (Pulchowk Campus, Institute of Engineering, Tribhuvan University, Patan), and THM (University Grants Commission Office, Sanothimi, Bhaktapur). The site locations are shown in Fig. 1a. We collected data using highly damped moving coil type (dimensionless damping constant h ~ 26, natural fre- quency of 3 Hz) Mitsutoyo JEP-6A3-2 accelerometers (Kudo et al. 2002) and Hakusan DATAMARK LS-8800 data loggers at a sampling rate of 100 Hz. The data loggers can perform GPS time calibration. Due to long hours of power outage in Kathmandu, the observation system is powered by chargeable batteries and voltage stabilizers for smooth operation. The accelerometer has a flat response (−3 dB) of ground acceleration from

The most important dynamic characteristics of earthquake are peak ground acceleration (PGA), frequency content, and duration. These characteristics play predominant rule in studying the behavior of structures under seismic loads. The strength of ground motion is measured based on the PGA, frequency content and how long the shaking continues. Ground motion has different frequency contents such as low, intermediate, and high. Present work deals with study of frequency content of ground motion on reinforced concrete (RC) buildings. Linear time history analysis is performed in structural analysis and design (STAAD Pro) software. The proposed method is to study the response of low, mid, and high-rise reinforced concrete buildings under low, intermediate, and high- frequency content ground motions. Both regular and irregular three-dimension two, six, and twenty- story RC buildings with six ground motions of low, intermediate, and high-frequency contents having equal duration and peak ground acceleration (PGA) are studied herein.

The occurrence of the historical and machine Earthquakes, near to the North Tabriz Fault in NW Iran is an evidence for the seismic activity of this fault, which records a historical earthquake with a magnitude more than 7. Using the existing experimental relations, seismicity, and the fault geo- metry, a Mw 7.7 earthquake scenario was defined. The stochastic finite-fault modeling based on a dynamic corner frequency shows good agreement with common attenuation patterns. The shake map illustrates that Baghmisheh, Roshtieh, Ellahieh, Valiamr, and Eram region on Tabriz are at high hazard areas, and the maximum acceleration is located at the north direction with the same azimuth similar to fault strike.

The mean value and standard deviation for all distances but the three magnitude intervals are listed in Table 2. The statistic features are stable as a whole and unusual in just a few intervals. It means that there are really not enough ob- served data in the interval. The values of standard deviation are comparable with those of empirical prediction in the re- gions with rich strong motion data. The facts show that it is possible to build an attenuation relation by small earthquake data recorded by regional broadband earthquake networks, for regions without enough strong ground motion records.

Topographic irregularities such as hills affect the amplification characteristics of strong ground motion. Due to the interference between direct waves and scattered waves, the behavior of seismic waves passing through irregular terrain is complex. In this study, records of seismic ground motion were compared to simulated seismic waves, calculated from 3-dimensional FEM. The study objectives were to build an analytical model capable of accurately reproducing the observed data and to evaluate the amplification characteristics of strong ground motion in areas characterized by irregular topography.

Seismic hazard estimation using modelling of earthquake strong ground motions: A brief analysis of 1991 Uttarkashi earthquake, Himalaya and prognostication for a great earthquake in [r]

The pseudo point-source model approximates the rupture process on faults with multiple point sources for simulat- ing strong ground motions. A simulation with this point-source model is conducted by combining a simple source spectrum following the omega-square model with a path spectrum, an empirical site amplification factor, and phase characteristics. Realistic waveforms can be synthesized using the empirical site amplification factor and phase models even though the source model is simple. The Kumamoto earthquake occurred on April 16, 2016, with M JMA 7.3. Many strong motions were recorded at stations around the source region. Some records were considered to be affected by the rupture directivity effect. This earthquake was suitable for investigating the applicability of the pseudo point- source model, the current version of which does not consider the rupture directivity effect. Three subevents (point sources) were located on the fault plane, and the parameters of the simulation were determined. The simulated results were compared with the observed records at K-NET and KiK-net stations. It was found that the synthetic Fou- rier spectra and velocity waveforms generally explained the characteristics of the observed records, except for under- estimation in the low frequency range. Troughs in the observed Fourier spectra were also well reproduced by placing multiple subevents near the hypocenter. The underestimation is presumably due to the following two reasons. The first is that the pseudo point-source model targets subevents that generate strong ground motions and does not consider the shallow large slip. The second reason is that the current version of the pseudo point-source model does not consider the rupture directivity effect. Consequently, strong pulses were not reproduced enough at stations northeast of Subevent 3 such as KMM004, where the effect of rupture directivity was significant, while the amplitude was well reproduced at most of the other stations. This result indicates the necessity for improving the pseudo point- source model, by introducing azimuth-dependent corner frequency for example, so that it can incorporate the effect of rupture directivity.

All the selected 25 building models with different plan aspect ratio and slenderness ratio are analyzed using commercial ETABS 13 software. This chapter presents the analysis result and relevant discussion based on analysis. According to objectives of present study, the results presented here are focused on storey shear, fundamental time period, lateral displacement and inter-storey drift. The details of selected building models and outline of analysis procedure followed in this study are in chapter 3

tems. Major developments in the theory, hardware, de- sign, specification, and installation of these systems have permitted significant applications to buildings, bridges, and industrial plants. Applications are now found in al- most all of the seismically active countries of the world, but principally in Italy, Japan, New Zealand, and the United States. There are, however, limitations to the use of passive systems, which deserve further study and re- search. They include the uncertainty of response in the near field of an active fault, the non-optimal behavior of passive systems for both small and large earthquakes, and a lack of certainty about the ultimate limit states in un- expectedly large events. This study shall provide deeper understanding of the behavior of passive control devices for seismic excitations of different magnitude.

nary variable equal to 1 in case respondents are Christians or Jews and 0 otherwise. Differently from them we find no significant results (column 4). The two findings, however, are not inconsistent, as Guiso et al. (2006) car- ried out their analysis at the cross-country level, where larger variability is observed. As reported in Table 1, roughly 92% of the Itanes sample declared to be Christian or Jew. In columns 5 and 6 we control for news consumption through television and the Internet to test for the possible role of informa- tion (see for example Kuzmienko et al., 2015). In either cases coefficients are not significant. We also control for the use of other types of media and contents, the work status of respondents and their self-reported interest in politics, with no significant results. 2

The coefficients of horizontal translational acceleration, x, and the horizontal components of grav- ¨ ity caused by the tilt, approximately gφ, are identical. Therefore the displacement, x, cannot be found by double integration of the output of the accelerometer [11]. Trifunac and Todorovska [10] have recently restated this although they use a slightly different equation of motion which includes cross-axis sensitivity. The equation of motion for instruments that measure vertical accelerations is not effected by tilts of the instrument [11]. If the effects of tilts on the recorded ground motion can be ignored then the recovery of the true ground displacement may be possible using an appropriate processing technique [5].

Current seismic hazard assessments express hazard in terms of a Uniform Hazard Spectrum (UHS). High frequency content is typically present in the UHS for Nuclear Power Plants (NPP) in Central and Eastern North America. It was found that this high frequency content in the UHS has significant effects on the seismic response of a structure when using conventional analysis methodologies. In several analytical cases, the high frequency content contributes to an increase in the floor response spectra, especially for those elevations close to the ground. In reality, however, it is well known that high frequency content of ground motion has much lesser damage effect to Structures, Systems, and Components (SSCs) of a NPP than low frequency content (except functional performance of some vibration sensitive components, such as relays). The challenge is how to reflect this reality in seismic analysis of a NPP.

As a simplified approach for estimating theor etically the influence of local subsoils upon the ground motion during an earth- quake, the problem of an idealized [r]