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1016 strong-motion records at 527 free-field stations and 131 records at 42 strong-motion arrays at buildings and bridges were obtained for the Pingtung earthquake doublet from the Taiwan Central Weather Bureau's dense, digital strong-motion network. We carried out standard processing of these strong-motion records at free-field stations. A data set, including the originally recorded files, processed data files, and supporting software and information, is archived online http://tecdc.earth.sinica.edu.tw/data/EQ2006Pingtung/. We have not yet completed the processing of the strong-motion array data at buildings and bridges. However, some preliminary results and the strong-motion array data recorded at the second nearest instrumented building to the Pingtung earthquake doublet are shown. This paper is intended to document our data processing procedures and the online archived data files, so that researchers can efficiently use the data. We also include two preliminary analyses: (1) a comparison of ground motions recorded by multiple accelerographs at a common site, the TAP117 station in Taipei, and (2) attenuation of the horizontal ground motions (peak acceleration and response spectra at periods of 0.2, 1.0, and 3.0 s) with respect to distance. Our comparison study of multiple recordings at TAP117 indicates that waveform coherence among 20- and 24-bit accelerograph records is much higher as compared to records from 16-bit or 12-bit accelerographs, suggesting that the former are of better quality. For the 20- and 24-bit accelerographs, waveform coherence is nearly 1 over the frequency range 1 to 8 Hz for all components, and is greater than about 0.9 from 8 to 20 Hz for the horizontal component, but only from 8 to 12 Hz for the vertical component. Plots of pseudo-acceleration response spectra (PSA) as a function of distance, however, show no clear indication for a difference related to the performance level of the accelerographs. The ground-motions of the first event (MW = 7.0) are comparable, or even somewhat lower, than those from the smaller second event (MW = 6.9), consistent with the relative difference of the local magnitudes (ML = 6.96 and 6.99 for the first and second events, respectively). The ground motions from the first event are generally lower than those predicted from equations based on other in-slab subduction earthquakes, whereas the ground motions from the second event are closer to the predictions. Ground-motions for soil sites are generally larger than those from rock sites. [ABSTRACT FROM AUTHOR]

With an estimated population of 7 million, the Taipei Metropolis (TM) is the largest metropolitan area in Taiwan. It included Taipei City, Keelung and New Taipei City. Taipei City serves as the core of the metropolitan area where the government of Taiwan and major commercial districts are located. It is also the home to one of the most famous high-rise buildings in the world, the Taipei 101 Tower. Taipei City is an area overlay hundreds meters thick of soft soil deposits, damage from the Hualien earthquake of 1986 and the Chi-Chi earthquake of 1999 was concentrated in areas underlain by soft soil deposits. To decrease amounts of damage due to amplification effects of soft soil deposits from earthquake ground shaking, a set of integrated arrays began to construct in 2005. This paper describes the design objectives of these arrays, their location, seismic and geologic information, and instrumentation configuration. [ABSTRACT FROM AUTHOR]

Locating earthquakes from the beginning of the modern instrumental period is complicated by the fact that there are few good-quality seismograms and what traveltimes do exist may be corrupted by both large phase-pick errors and clock errors. Here, we outline a Bayesian approach to simultaneous inference of not only the hypocentre location but also the clock errors at each station and the origin time of the earthquake. This methodology improves the solution for the source location and also provides an uncertainty analysis on all of the parameters included in the inversion. As an example, we applied this Bayesian approach to the well-studied 1909 Mw 7 Taipei earthquake. While our epicentre location and origin time for the 1909 Taipei earthquake are consistent with earlier studies, our focal depth is significantly shallower suggesting a higher seismic hazard to the populous Taipei metropolitan area than previously supposed. [ABSTRACT FROM AUTHOR]

SUMMARY The 1909 April 14 Taiwan earthquake caused significant damage in Taipei. Most of the information on this earthquake available until now is from the written reports on its macro-seismic effects and from seismic station bulletins. In view of the importance of this event for assessing the shaking hazard in the present-day Taipei, we collected historical seismograms and station bulletins of this event and investigated them in conjunction with other seismological data. We compared the observed seismograms with those from recent earthquakes in similar tectonic environments to characterize the 1909 earthquake. Despite the inevitably large uncertainties associated with old data, we conclude that the 1909 Taipei earthquake is a relatively deep (50-100 km) intraplate earthquake that occurred within the subducting Philippine Sea Plate beneath Taipei with an estimated MW of 7 ± 0.3. Some intraplate events elsewhere in the world are enriched in high-frequency energy and the resulting ground motions can be very strong. Thus, despite its relatively large depth and a moderately large magnitude, it would be prudent to review the safety of the existing structures in Taipei against large intraplate earthquakes like the 1909 Taipei earthquake. [ABSTRACT FROM AUTHOR]

The Taipei basin in northern Taiwan is located in a high seismicity region and was affected by several earthquakes in the past ( on 1909 April 15; on 1986 November 15; the Chi-Chi earthquake on 1999 September 21 and on 2002 March 31). The main characteristic of the Taipei basin is its complex shape with a deep western and shallow eastern part. The uppermost Sungshan formation with its low shear wave velocities (90-200 m s) is also a distinct feature of the basin. Based on the large data base of earthquake records obtained from the Taiwan Strong Motion Instrumentation Program network, many studies on ground motion within the Taipei basin exist. However, the influence of the various subsurface structures on the observed ground motions as well as the variability of ground motion with respect to earthquake location is not fully understood. We apply a 3-D finite-difference method to simulate wave propagation up to 1 Hz for a small earthquake close to the basin in order to resolve these open questions. By varying source and structural parameters, we explore the variability of ground motion. Our study includes a subsurface model that is based on recent studies on the basin structure and on the crustal structure of Taiwan. From our simulations we find a good fit between simulated and observed waveforms and peak ground accelerations for the considered small earthquake near the basin. We also explore the influence of fault plane orientation, hypocentre location, deep basin structure and soft soil surface layers of the Sungshan formation by varying the subsurface structure and earthquake position. Our studies reveal that the basin structure produces an amplification factor of about 4 compared to hard rock conditions. Additionally, the soft soil Sungshan formation produce amplification of a factor of 2. This results in a maximum amplification of the basin structure of about 8, which is in good comparison with amplification values larger than 5 found from the analysis of observed earthquakes. These values clearly exceed the amplification values of about 2-3 obtained when applying standard 1-D site effect analysis. Our simulations for different earthquake positions show that ground motion depends strongly on earthquake location and fault orientation. Therefore, the application of average values of spectral amplification obtained from the analysis of recorded data from distant earthquakes with different azimuths and fault planes may significantly underestimate future ground motions of possible earthquakes on known faults close to the Taipei basin. The simulation of a small earthquake near the Taipei basin presented in this study will help to set up adequate simulation parameters for a possible large earthquake close to the Taipei basin. Such a simulation of a scenario earthquake close to the Taipei basin would allow to significantly improve hazard assessment as no observations of strong earthquakes in the vicinity of the basin exist. [ABSTRACT FROM AUTHOR]