## 6 Conclusions  
In this study, we investigated the response spectra of eight stations for horizontal and vertical components in the Jeju area and explored the effects of earthquake magnitude on the resonance frequencies of buildings and other structures. Furthermore, we compared the response spectra of the eight stations to that of Reg. Guide 1.60 (anchored to 0.3 g) and KBC 2016 (2400-year return period) seismic design standards. The results can be summarized as follows:  
1. We analyzed 24 macro-earthquakes, including the Kumamoto main shock (2016-04-16, ML; 7.3) and Pohang main shock (2017-11-15, ML; 5.4). Their response spectra showed characteristics similar to the typical design response spectrum shapes, as suggested by the various design standards, Reg Guide 1.60, 1.165, and 1.208 (US NRC 1973, 1997, 2007) and ASME ([PERSON] and [PERSON], 2017) [10; 17; 20; 21]. 2. The vertical response spectra of the eight stations were consistently lower than the vector-summed horizontal spectra, which was in good agreement with the V/H scales suggested by various seismic design standards (Table 3). Furthermore, the vertical response spectra clearly indicated magnitude dependence in the lower frequency band. 3. When establishing design response spectra that represents an arbitrary region or the Jeju region, it is necessary to consider a number of fairly large magnitudes of earthquakes (ML 6.0 or larger) considering the earthquake magnitude is essential for determining the characteristics of the response spectrum, especially in the low-frequency  
Figure 12: Comparison of the response spectra of 8 stations with KBC (2016) for SC, SD, and SE soil conditions (2400-years return periods). The \(x\)- and \(y\)-axes represent the structure resonance period and response spectrum, respectively. bands suggested in this and other studies. Fairly large earthquake magnitudes, e.g., M\({}_{\rm L}\) 6.0 or larger, secure conservatism in the low-frequency ranges suggested by this study and other studies and are also important to reduce variability of observed response spectra. Considering the rare occurrence of seismic activities of ML 6.0 or larger in the Korean Peninsula, it is necessary to collect seismic ground motions from the south-eastern region of Japan, which is geographically closer to the Korean Peninsula, where earthquakes of ML 6.0 or larger occur frequently. * Compared to that of inland areas, the maximum horizontal response in the Jeju area was fairly higher (\(\sim\)12%-13 %), whereas the frequency band with high responses at the peak (\(\sim\)2.0-6.0 Hz) was significantly lower. This could be attributed to the local geological environment of Jeju Island, which was formed mainly by a surface volcano eruption with lower shear velocity and is related to the existence of unconsolidated Pleistocene marine sediments distributed widely in the area. Further studies are necessary to understand the characteristic influence of layers with low shear wave velocity distributed in the Jeju region on the seismic responses based on the frequency band and amplitudes at the surface of Jeju. * In this study, most frequency ranges with very high responses, including the peak, overlapped with the resonance frequencies of general low-rise and mid-rise buildings (2-story-7 story) considering both the brief formula and design response spectra suggested by KBC 2016, in contrast to frequencies higher than \(\sim\) 9 Hz in inland areas, which is far from the resonance frequency band. Owing to this, the seismic hazard on general buildings in the Jeju region could be much higher than that in inland areas. Therefore, it is necessary to establish an improved design response spectrum with site-specific response spectra in Jeju or to alter existing standards by applying natural resonance frequency ranges that are different from that of the inland areas. * For the construction of nuclear facilities in the Jeju area, the seismic design code for nuclear facilities as suggested in Reg.