# Compatible Ground Motion Models for South Korea Using Moderate Earthquakes
## 1 Introduction  
A ground motion model (GMM), also known as a ground motion prediction equation or attenuation relationship, is used to estimate ground motion intensity measures at a specific location as a result of an earthquake. GMMs make such estimates using parameters, such as earthquake magnitude, site-to-source distance, local site effects, and source effects [1]. Numerous comprehensive studies have actively explored these factors. The Pacific Earthquake Engineering Research Center (PEER) became one of the leaders in this field from the time of its establishment in 1997. PEER initiated comprehensive earthquake research and published extensive studies, including GMM and seismic hazard analyses, with a primary focus on the frequent seismic activity in the Western United States [1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12]. On the other hand, in the context of South Korea, earthquake-related studies have received limited attention due to the region's perceived low seismicity, where South Korea is classified as a moderate seismic-hazard zone, which corresponds to a maximum acceleration on a rock site of 0.2-0.8 m/s\({}^{2}\), with a 10% probability of exceedance in 50 years or, in other words, having a 475-year return period [13]. Between the initiation of earthquake observation in 1905 until 2006, approximately 1000 earthquakes have been recorded, with the majority being small events with a magnitude of less than 4.0 [14]. Additionally, the average annual frequency of earthquakes stood at 19.1 from 1978 to 1998. However, there was a significant increase in the average frequency to 70.6 after 1999, following the initiation of digital recording for earthquake monitoring [15]. This notable rise can be attributed, in part, to the occurrence of major earthquakes in Gyeongju (M\({}_{\rm W}\) 5.5, 2016) and Pohang (M\({}_{\rm W}\) 5.5, 2017) [16; 17]. These events led to heightened concerns about earthquake vulnerability on the Korean Peninsula and to increased attention. With the growing focus on earthquake and earthquake risk studies on the Korean peninsula, several challenges have emerged in local seismology and earthquake engineering analyses. For example, studies on active faults in the Korean peninsula were insufficient from the government's perspective, which started programs to investigate specific faults in South Korea in 2017, and the Korean Ministry of the Interior and Safety announced that this research will be completed in 2041 [18]. Moreover, there have been additional issues in how earthquake data are processed by the Korea Meteorological Agency (KMA). The KMA has reported earthquake magnitude measurements using the local magnitude scale (M\({}_{\rm L}\)) derived from Japanese studies since 1978 [19]. Regrettably, the M\({}_{\rm L}\) equation was formulated based on Japanese earthquake events over M\({}_{\rm L}\) 5.0, incorporating geological characteristics specific to Japan, making it inappropriate for South Korea [20; 21]. KMA has made a series of adjustments, continues to employ M\({}_{\rm L}\), and does not show a willingness to adopt moment magnitude (M\({}_{\rm W}\)) as an earthquake magnitude scale, one that is widely utilized throughout the world. To compound the problem, the aforementioned data are crucial elements in GMMs, making it very difficult to apply robust GMMs in earthquake and seismic risk studies around the Korean peninsula. Additionally, there is a lack of guidance on which GMMs are appropriate for use in the Korean peninsula, with only one model developed using small-magnitude earthquakes from 2007 to 2012 [22]. Other countries and regions have also shown an interest in comparing appropriate GMMs for seismic hazard studies [23; 24; 25] or developing localized GMMs for better use [6; 7; 26; 27; 28]. These studies generally evaluate performance using secondary computations on residuals, with some selecting a small band of relevant intensity measures for evaluation [23; 24].