• 한국지구물리탐사학회:학술대회논문집
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• 2005.05a
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• pp.93-101
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• 2005

Seismicity changes associated with foreshocks of large Korean historical earthquakes of MMI > VIII are investigated for earthquake prediction study. A number of tests showed that b-values of foreshocks associated with these large earthquakes are most stable for precursor period of 13 years before the earthquake and rectangular source area of $1.1^{\circ}$ by $1.1^{\circ}$ around the epicenter. The b-values of foreshocks for 11 large events of MMI > VIII for the above foreshock area and precursor period turns out to be smaller than the value of 0.36 for the whole historical earthquakes with average 0.27. Epicenters of these foreshocks of small b-values are distributed close to the location of the main large earthquake. These observations indicate a possibility of predicting large earthquakes by closely monitoring the change of b-value for an extended period over decades in the Korean peninsula.

• Journal of the Korean Geophysical Society
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• v.8 no.3
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• pp.115-121
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• 2005

Seismicity changes associated with foreshocks of large Korean historical earthquakes of MMI > VIII are investigated for earthquake prediction study. A number of tests showed that b-values of foreshocks associated with these large earthquakes are most stable for precursor period of 13 years before the earthquake and rectangular source area of 1.1o by 1.1o around the epicenter. The b-values of foreshocks for 11 large events of MMI > VIII for the above foreshock area and precursor period turns out to be smaller than the value of 0.36 for the whole historical earthquakes with average 0.27. Epicenters of these foreshocks of small b-values are distributed close to the location of the main large earthquake. These observations indicate a possibility of predicting large earthquakes by closely monitoring the change of b-value for an extended period over decades in the Korean peninsula.

• Earthquakes and Structures
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• v.8 no.1
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• pp.153-184
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• 2015

Most damaging earthquakes come as complex sequences characterized by strong aftershocks, sometimes by foreshocks and often by multiple mainshocks. Complex earthquake sequences have enormous seismic hazard, engineering and societal implications as their impact on buildings and infrastructures may be much more severe at the end of the sequence than just after the mainshock. In this paper we examine whether historical sources can help characterizing the rare earthquake sequences of pre-instrumental times in full, including fore-, main- and aftershocks. Thanks to the its huge documentary heritage, Italy relies on one of the richest parametric earthquake catalogues worldwide. Unfortunately most current methods for assessing seismic hazard require that earthquake catalogues be declustered by removing all shocks that bear some dependency with those identified as mainshocks. We maintain that this requirement has led most modern historical seismologists to focus mainly on mainshocks rather than also on the fore- and aftershocks. To shed light onto major earthquake sequences of the past, rather than onto individual mainshocks, we investigated 10 damaging earthquake sequences ($M_w$ 4.7-7.0) that hit the L'Aquila area and central Abruzzo from the 14th to the 20th century. We find that most of the results of historical research are important for modern seismology, yet their rendering by the current parametric catalogues causes most information to be lost or not easily transferred to the potential users. For this reason we advocate a change in current strategies and the creation of a more flexible standard for storing and using all the information made available by historical seismology.

• Structural Engineering and Mechanics
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• v.32 no.4
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• pp.563-581
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• 2009

In this paper, the peak horizontal ground acceleration over the bedrock (PGA) is calculated by a probabilistic seismic hazard assessment (PSHA). For this reason, at first, all the occurred earthquakes in a radius of 200 km of Sanandaj city have been gathered. After elimination of the aftershocks and foreshocks, the main earthquakes were taken into consideration to calculate the seismic parameters (SP) by Kijko (2000) method. The seismotectonic model of the considered region and the seismic sources of the region have been modeled. In this research, Sanandaj and its vicinity has been meshed as an 8 (vertical lines) * 10 (horizontal lines) and the PGA is calculated for each point of the mesh using the logic tree method and the five attenuation relationships (AR) with different weighted coefficient. These calculations have been performed by the Poisson distribution of four hazard levels. Then by using it, four regional maps of the seismic hazard regions have been provided for Sanandaj and its vicinity. The results show that the maximum and minimum value of PGA for the return periods of 75, 225, 475, 2475 years are (0.114, 0.074) (0.157, 0.101), (0.189, 0.121) and (0.266, 0.170), respectively.

• Earthquakes and Structures
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• v.18 no.2
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• pp.147-162
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• 2020

This paper presents a novel precast energy dissipation shear wall (PEDSW) structure system that using mild steel dampers as dry connectors at the vertical joints to connect adjacent wall panels. Analytical studies are systematically conducted to investigate the seismic performance of the proposed PEDSW under sequence-type ground motions. During earthquake events, earthquake sequences have the potential to cause severe damage to structures and threaten life safety. To date, the damage probability of engineering structures under earthquake sequence has not been included in structural design codes. In this study, numerical simulations on single-story PEDSW are carried out to validate the feasibility and reliability of using mild steel dampers to connect the precast shear walls. The seismic responses of the PEDSW and cast-in-place shear wall (CIPSW) are comparatively studied based on nonlinear time-history analyses, and the effectiveness of the proposed high-rise PEDSW is demonstrated. Next, the foreshock-mainshock-aftershock type earthquake sequences are constructed, and the seismic response and fragility curves of the PEDSW under single mainshock and earthquake sequences are analyzed and compared. Finally, the fragility analysis of PEDSW structure under earthquake sequences is performed. The influences of scaling factor of the aftershocks (foreshocks) to the mainshocks on the fragility of the PEDSW structure under different damage states are investigated. The numerical results reveal that neglecting the effect of earthquake sequence can lead to underestimated seismic responses and fragilities, which may result in unsafe design schemes of PEDSW structures.

• Korean Journal of Remote Sensing
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• v.34 no.6_4
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• pp.1489-1501
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• 2018

In 2016 Kumamoto, Japan, the foreshocks of $M_j$ 6.5 and 6.4, mainshock of $M_j$ 7.3 besides more than 2,000 aftershocks occurred in succession. Large surface deformation occurred due to this serial earthquakes and three-dimensional measurements of the deformation have been presented for the study of fault structures (Baek, 2017). The 3d measurements retrieved from two ascending pairs (20160211_20160602, 20151119_20160616) and a descending pair (20160307_20160418) acquired from ALOS PALSAR-2. In order to avoid mixing ionospheric error components on along-track surface deformation, the descending multiple-aperture interferogram, which do not contain the deformation of aftershocks after 20160418, was utilized. For these reason, there was a temporal discrepancy of about 2 months in extracting the north-south deformation. In this study, we applied a directional filter based ionospheric correction to ascending multiple-aperture interferograms, in order to reduce this discrepancy and understand more accurate fault movements. As a result of the ionospheric correction, an additional displacement signal was observed nearby fault lines. The root-mean-squared errors compared to GPS were about 9.87, 8.13 cm respectively. These results show improvements of 4.8 and 6.4 times after ionospheric correction. We expected that these along-track measurements would be used to decide more accurate movements of faults related to the 2016 Kumamoto Earthquake.