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The active Milun Fault is the northernmost segment of the suture between Philippine Seaplate and Eurasian plate on the Taiwan Island. Historically, it was linked to two destructiveearthquakes on October 22nd, 1951, and February 6th, 2018, respectively. The 1951 ML7.3earthquake and the 2018 MW6.4 earthquake both produced surface ruptures along the MilunFault, causing casualties and damage on buildings in the Hualien city, which is the mostpopulated area in eastern Taiwan. Although the Milun Fault is surely intimidating, thesubsurface configuration and history of this active fault remain little exposed. The purpose ofthis study is to uncover the fault at shallow depth, reason the activity and seismic history ofthe Milun Fault and estimate the recurrence interval. Two trenches along with four boreholeswere carried out six months after the shock at the study site, located ∼ 2.6 kmnorth of downtown Hualien, where surface ruptures were reported during the 2018earthquake. The walls of one trench revealed a high dip angle of 80˚ to the east forthe main fault of the Milun Fault and its branch faults dip 36˚, 56˚, and 70˚ tothe east, respectively. The growth strata in the footwall of the branch faults werefolded. Distinctive sedimentary features such as the colluvial-wedge deposits andsoil liquefaction were also observed on the trench walls. By compiling the resultsof restoration and stripping of strata in conjunction with the age constraints, fivepaleo-earthquake events associated with the Milun Fault are resolved: (1) the 2018 event andthe earlier ones occurred at (2) 380-0 yr BP (3) 686-380 yr BP (4) 2184-1396 yrBP (5) 3232-2630 yr BP. Although the recurrence interval was estimated as ca.70 yrs earlier, our data suggest that the recurrence interval could be longer thanpreviously expected. However, due to the limited records of stratigraphy and possibleabsence of paleo-earthquakes, further investigation will be needed to generate a moresophisticated estimate of the recurrence interval. In addition, based on the borehole data,the slip rate of the Milun fault is about 6.0 to 6.5 mm/yr within the past 5000 yrs.These new findings shall benefit the earthquake hazard assessment for the region. [ABSTRACT FROM AUTHOR]

In order to avoid the casualties caused by damaged buildings during strong earthquakes, it's important and essential to understand the seismic design specifications of buildings. The motion of a building depends on the interferometry of building and ground motion, the coupling between building and ground, and the mechanical properties of the building. We applied deconvolution to the motion recorded to separate the building response. Deconvolution interferometry is a powerful and convenient tool which allow us to extract structural parameters (e.g., shear wave velocity, resonance frequency and attenuation parameter) from seismic records. By applying deconvolution to earthquake records, it can provide a complete response of the building and understanding the motion pattern of the structure under strong motion. Therefore, we can check medium's state by tracking resonance frequency, shear wave velocity and the attenuation parameter Q to avoid damage of building in the next mega-earthquake. We deployed a seismograph array in the library of National Chung Cheng University, Taiwan, which recorded earthquakes and few months of ambient noise record. The shear wave velocity from the seismic record was calculated to be 225.26±24.29 m/s. We also used seismic record to calculate the Q value of each floor and found that the Q value for the lower floors (Q=16) was lesser on average than the higher floors (Q=23). We believe that this reflects partial energy of the wave dissipated to the surface during transfer, making the Q value of the lower floors is lesser. On the other hand, we estimated the similar shear wave velocity 289.9±7.6 m/s from ambient noise record for the entire building as well. In advance, we divided the structure into low- and high-floors to calculate the shear wave velocity from the upward and downward propagation. We found that the shear wave velocities of the low and high floors are significantly different but exhibit a stable variation. For the monitoring phase, calculating the velocity variation from ambient noise depends on stacking signal to gain better S/N ratio and more convergent result. Therefore, for ambient noise calculation, we tried different stacking time-lengths and calculated the related shear wave velocities which the results are similar to the analysis in earthquake. From the above results, we concluded that the physical parameters of the building are stable and implied that the structure is in a healthy condition. Finally, we hope these results would be helpful to build a long-term monitoring of building's healthy status and the assessment of seismic hazard. [ABSTRACT FROM AUTHOR]

The seismic source spatiotemporal rupture process of events in Japan, Taiwan and Greece are imaged by backprojection of strong motion waveforms. Normalized high frequency (>2Hz) S-waveforms from recordings on dense strong-motion networks are used to scan a predefined 3D source volume over time. Backprojection is an alternative novel approach to image the spatiotemporal earthquake rupture. The method was firstly applied for large earthquakes at teleseismic distances but is nowadays used at local distances and higher frequencies. The greatest advantage of the method is that processing is done without any a-priori constraints on the geometry, dimension and size of the source. Thus, the spatiotemporal imaging of the rupture is feasible in higher frequencies (> 1Hz) than conventional source inversion studies even when the examined fault geometry is complex. This high frequency energy emitted during an earthquake is of great importance in seismic hazard assessment for certain critical infrastructures. The actual challenge in using high frequency local records is to distinguish the local site effects from the true earthquake source content. Otherwise, mapping them incorrectly to the source area limits the resolvability of the method. The real challenge is to remove the site effect part from all available records, or at least, to distinguish quantitatively good reference stations from hard-soil and rock sites. In this study, the advantages and limitation of the method are explored using waveform data from well recorded events in Japan (Hokkaido Eastern Iburi Earthquake, 2018, Kumamoto 7.1 Mw, 2016), Taiwan (Hualien 6.4 Mw, 2018) and Greece (Zakinthos 6.8 Mw, 2018). [ABSTRACT FROM AUTHOR]

We present earthquake shaking scenarios by a physics-based ground-motion simulation scheme for seismic risk assessments. In fitting requirements of the application of loss estimations, scenarios can refer to various kinds of damage and losses to constructions (buildings, bridges, etc.), casualties, economic losses, social losses and so on. We quantitatively assess the ground motion effects by the physics-based full-waveform ground-motion simulation which is a powerful tool for earthquake-induced ground-motion prediction. The entire time history of the ground motion induced by an earthquake depends on a number of factors, including source-rupture process, subsurface velocity structure, topographic relief, and local site condition. Then, the further risk assessment can also be revealed by a combination with exposure data. As an example, we carried out simulations to model rupture scenario of the Shanchiao fault and the potential large subduction earthquake in northern Taiwan, with accounting for effects of (1) source slip distribution, (2) seismic wave propagation, (3) surface topography and (4) site amplification. Output ground-motion parameters, including peak ground acceleration (PGA), peak ground velocity (PGV), peak ground displacement (PGD), 0.3-s-period spectral acceleration (SA0.3), and 1.0-s-period spectral acceleration (SA1.0), can be adopted to further implement to loss estimation. Our results referred different shaking-level potentials of earthquake scenarios can benefit to risk management, especially for the further application of strategy making of emergency response and disaster prevention and preparations. [ABSTRACT FROM AUTHOR]