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  • Articles  (32)
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  • 1
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    Anatomy of the high-frequency ambient seismic wave field at the TCDP borehole (2012)
    Wiley
    Details
    Publication Date: 2012-06-01
    Description: The Taiwan Chelungpu-fault Drilling Project (TCDP) installed a vertical seismic array between 950 and 1270 m depth in an active thrust fault environment. In this paper we analyze continuous noise records of the TCDP array between 1 and 16 Hz. We apply multiple array processing and noise correlation techniques to study the noise source process, properties of the propagation medium, and the ambient seismic wave field. Diurnal amplitude and slowness patterns suggest that noise is generated by cultural activity. The vicinity of the recording site to the excitation region, indicated by a narrow azimuthal distribution of propagation directions, leads to a predominant ballistic propagation regime. This is evident from the compatibility of the data with an incident plane wave model, polarized direct arrivals of noise correlation functions, and the asymmetric arrival shape. Evidence for contributions from scattering comes from equilibrated earthquake coda energy ratios, the frequency dependent randomization of propagation directions, and the existence of correlation coda waves. We conclude that the ballistic and scattered propagation regime coexist, where the first regime dominates the records, but the second is weaker yet not negligible. Consequently, the wave field is not equipartitioned. Correlation signal-to-noise ratios indicate a frequency dependent noise intensity. Iterations of the correlation procedure enhance the signature of the scattered regime. Discrepancies between phase velocities estimated from correlation functions and in-situ measurements are associated with the array geometry and its relative orientation to the predominant energy flux. The stability of correlation functions suggests their applicability in future monitoring efforts.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Isotropic events observed with a borehole array in the Chelungpu fault zone, Taiwan (2012)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2012-07-28
    Description: Shear failure is the dominant mode of earthquake-causing rock failure along faults. High fluid pressure can also potentially induce rock failure by opening cavities and cracks, but an active example of this process has not been directly observed in a fault zone. Using borehole array data collected along the low-stress Chelungpu fault zone, Taiwan, we observed several small seismic events (I-type events) in a fluid-rich permeable zone directly below the impermeable slip zone of the 1999 moment magnitude 7.6 Chi-Chi earthquake. Modeling of the events suggests an isotropic, nonshear source mechanism likely associated with natural hydraulic fractures. These seismic events may be associated with the formation of veins and other fluid features often observed in rocks surrounding fault zones and may be similar to artificially induced hydraulic fracturing.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Ma, Kuo-Fong -- Lin, Yen-Yu -- Lee, Shiann-Jong -- Mori, Jim -- Brodsky, Emily E -- New York, N.Y. -- Science. 2012 Jul 27;337(6093):459-63. doi: 10.1126/science.1222119.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth Sciences, and Institute of Geophysics, National Central University, Taiwan, Republic of China. fong@ncu.edu.tw〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22837526" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 3
    Electronic Resource
    Electronic Resource
    Temporal variation of codaQ during Hualien earthquake of 1986 in eastern Taiwan (1989)
    Springer
    Pure and applied geophysics 130 (1989), S. 617-634 
    Details
    ISSN: 1420-9136
    Keywords: CodaQ ; envelope decay curve ; temporal variation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The May 20, 1986, Hualien earthquake sequence occurred on the northeastern coast of Taiwan. TheM=6.1 (GS mb) mainshock was followed by a large number of closely-clustered aftershocks with the largest being anM=5.5 event. One seismic station, TWD of the Taiwan Telemetered Seismographic Network, is located in the surface projection of the source region and provides excellent recordings of the entire earthquake sequence. These recordings, plus events occurring in the same source area preceding the mainshock, offer a unique opportunity to study the spatial and temporal variations of codaQ in a region of active subduction. A simple technique is devised that uses the envelope of the coda waveform to enable a quick determination of the codaQ from drum records. For recordings with a peak power at about 8 Hz, the following findings have been obtained: 1. The ambient codaQ near an active subduction region was as low as 145; 2. There was no significant decrease in codaQ within the period beginning one year and four months prior to the mainshock; 3. There was a significant drop of codaQ immediately after the mainshock; this drop lasted approximately two days before returning to the ambient level; 4. CodaQ values varied with focal depth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00881601
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  • 4
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    Probabilistic Seismic Hazard Analysis at Regional and National Scales: State of the Art and Future Challenges (2020)
    American Geophysical Union
    Details
    Publication Date: 2020-09-01
    Description: Seismic hazard modeling is a multidisciplinary science that aims to forecast earthquake occurrence and its resultant ground shaking. Such models consist of a probabilistic framework that quantifies uncertainty across a complex system; typically, this includes at least two model components developed from Earth science: seismic source and ground motion models. Although there is no scientific prescription for the forecast length, the most common probabilistic seismic hazard analyses consider forecasting windows of 30 to 50 years, which are typically an engineering demand for building code purposes. These types of analyses are the topic of this review paper. Although the core methods and assumptions of seismic hazard modeling have largely remained unchanged for more than 50 years, we review the most recent initiatives, which face the difficult task of meeting both the increasingly sophisticated demands of society and keeping pace with advances in scientific understanding. A need for more accurate and spatially precise hazard forecasting must be balanced with increased quantification of uncertainty and new challenges such as moving from time‐independent hazard to forecasts that are time dependent and specific to the time period of interest. Meeting these challenges requires the development of science‐driven models, which integrate all information available, the adoption of proper mathematical frameworks to quantify the different types of uncertainties in the hazard model, and the development of a proper testing phase of the model to quantify its consistency and skill. We review the state of the art of the National Seismic Hazard Modeling and how the most innovative approaches try to address future challenges.
    Description: Published
    Description: e2019RG000653
    Description: 6T. Studi di pericolosità sismica e da maremoto
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 5
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    Evidence for non-self-similarity of microearthquakes recorded at a Taiwan borehole seismometer array (2016)
    Oxford University Press
    Details
    Publication Date: 2016-05-29
    Description: We investigate the relationship between seismic moment M 0 and source duration t w of microearthquakes by using high-quality seismic data recorded with a vertical borehole array installed in central Taiwan. We apply a waveform cross-correlation method to the three-component records and identify several event clusters with high waveform similarity, with event magnitudes ranging from 0.3 to 2.0. Three clusters—Clusters A, B and C—contain 11, 8 and 6 events with similar waveforms, respectively. To determine how M 0 scales with t w , we remove path effects by using a path-averaged Q . The results indicate a nearly constant t w for events within each cluster, regardless of M 0 , with mean values of t w being 0.058, 0.056 and 0.034 s for Clusters A, B and C, respectively. Constant t w , independent of M 0 , violates the commonly used scaling relation ${t_w} \propto M_0^{1/3}$ . This constant duration may arise either because all events in a cluster are hosted on the same isolated seismogenic patch, or because the events are driven by external factors of constant duration, such as fluid injections into the fault zone. It may also be related to the earthquake nucleation size.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 6
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    Efficient waveform inversion for average earthquake rupture in three-dimensional structures (2014)
    Oxford University Press
    Details
    Publication Date: 2014-07-04
    Description: Advances in observational, theoretical and computational technologies have made it possible for automatic, real-time solutions of the focal mechanisms of earthquake point sources. However, for earthquakes of moderate and greater magnitudes, the complexity of the source kinematic processes often requires additional characteristics on the source rupture in order to make seismotectonic inferences and to explain the observed directivity effects of the radiation of seismic energy. We develop an efficient and effective approach to determining the average finite-rupture models of moderate earthquakes by fitting synthetic and recorded broadband waveforms. A Green's tensor database is established using 3-D structural model with surface topography to enable rapid evaluations of accurate synthetic seismograms needed for source parameter inversions without the need for high-performance computing. We take a two-step strategy: In the first step, a point-source model is determined by a grid search for the best fault-plane solution. Then, taking the two nodal planes in the point-source model as candidates of the actual fault plane, a second grid search is carried out over a suite of simplified finite-rupture models to determine the optimal direction and speed of the integrated rupture of the finite source. We applied our method to four moderate events ( M W 6) in southeastern Taiwan. Results show that our technique provides an effective choice in semi-automatic, near real-time determinations of finite-source parameters for earthquake hazard assessment and mitigation purposes.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 7
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    Efficient Inversions for Earthquake Slip Distributions in 3D Structures (2016)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2016-11-04
    Description: Advances in observational and computational seismology in the past two decades have made it possible for fully automatic and real-time determinations of the focal mechanisms of point earthquake sources. However, sources of all large and small earthquakes are intrinsically finite and heterogeneous, both temporally as well as spatially. Therefore, a full picture of the source slip distribution is essential not only for a better understanding of earthquake physics but also for accurate account of the source directivity effect for reliable and realistic predictions of earthquake-induced strong ground motions. We develop a source inversion technique that combines a well-established slip-distribution inversion method and an efficient algorithm for computing accurate synthetics in 3D structures based on a pre-established strain Green tensor database. This new technique makes it practical for slip-distribution inversion in 3D structures, which not only enhances the capability of resolving source slip distributions of moderate earthquakes through better accounting of the effects of lateral structural heterogeneities but also provides an effective tool for the development of automatic systems for near-real-time inversions of earthquake source slip distributions for seismic-hazard mitigation purposes.
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America (SSA)
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  • 8
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    Appraising the PSHA Earthquake Source Models of Japan, New Zealand, and Taiwan (2016)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2016-11-04
    Description: Earthquake-hazard models are one of the major contributions provided by the seismological community to tangibly support disaster risk reduction policies at a national level. Although the societal impact of hazard analyses can be huge, the development of models remains a scientific activity developed within frameworks that have a strong national emphasis and partial international recognition. However, broad acceptability of hazard models is a key aspect for achieving authoritativeness and a prerequisite for warranting that their construction is completed using well-recognized methodologies. As part of an enduring international collaboration between leading organizations operating in the hazard and risk fields in Japan, New Zealand, Taiwan, and the Global Earthquake Model initiative, we discuss the main characteristic of the earthquake source models—as implemented for the OpenQuake engine—used for the calculation of the most recent national seismic-hazard maps of these three countries. Particular emphasis is placed on comparing the various modeling options adopted in the different tectonic regions, on emphasizing commonalities, and on discussing the most controversial modeling solutions. Despite the many connections from a seismotectonic point of view between the three countries, the comparison highlights different modeling choices for the various tectonic regions, which constitute a spectrum of possible epistemic uncertainties, as well as modeling issues that could be collectively explored in future phases of this international collaboration.
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America (SSA)
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  • 9
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    An Investigation of the Reliability of the Taiwan Earthquake Model PSHA2015 (2016)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2016-11-04
    Description: The Taiwan Earthquake Model (TEM) has had a new probabilistic seismic-hazard analysis (PSHA) model for determining the probability of exceedance (PoE) of the ground motion over a specified period in Taiwan. We conducted several tests to investigate the adequacy of the seismic source parameters adopted by the TEM in 2015 (TEM PSHA2015). The observed maximal peak ground accelerations (PGAs) of the M L 〉4.0 mainshocks from 1993 to 2015 were used to test the predicted PGA from areal and subduction zone sources based on a time-independent Poisson distribution. This comparison excluded the observations from the 1999 Chi-Chi earthquake, because this was the only earthquake associated with the identified active fault in the testing period. We used tornado diagrams to analyze the sensitivities of these source parameters to the ground-motion values of the PSHA. This study showed that the predicted PGA for a 63% PoE in the 23-year period corresponded to observations, confirming the applicability of the parameters to areal and subduction zone sources. We adopted disaggregation analysis to determine the contribution of each seismic source to the hazard for six metropolitan cities in Taiwan. Sensitivity tests on the seismogenic structure parameters indicated that slip rate and maximum magnitude are the dominant factors in the TEM PSHA2015. For densely populated faults in southwestern Taiwan, the assessed hazard level is more sensitive to the maximum magnitude of earthquakes than it is to the slip rate of active faults, creating concern for the possibility of larger earthquakes due to multiple-segment ruptures in this area, which has not yet been considered in the TEM PSHA2015. The source category disaggregation also suggested a seismic hazard over long periods in northern Taiwan due to subduction zone sources.
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America (SSA)
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  • 10
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    Implications of the Great Mw 9.0 Tohoku-Oki Earthquake on the Understanding of Natural Hazard in Taiwan and New Zealand (2016)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2016-11-04
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America (SSA)
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