###### Abstract  
The unprecedentedly strong 2016 Gyeongju and 2017 Pohang earthquakes on the Korean Peninsula aroused public concern regarding seismic hazards previously considered improbable. In this study, we investigated the effects of recent seismic activity close to the epicenters of both earthquakes in the heavy industrial complex of Ulsan. This was performed using Sentinel-1 InSAR time series data combined with on-site GPS observations and background GIS data. The interpretations revealed ongoing topographic deformation of a fault line and surrounding geological units of up to 15 mm/year. Postseismic migrations through the fault line, coupled with the two earthquakes, were not significant enough to pose an immediate threat to the industrial facilities or the residential area. However, according to InSAR time series analyses and geophysical modelling, strain from the independent migration trend of a fault line and eventual/temporal topographic changes caused by potential seismic friction could threaten precisely aligned industrial facilities, especially chemical pipelines. Therefore, we conducted probabilistic seismic hazard and stress change analyses over surrounding areas of industrial facilities employing modelled fault parameters based on InSAR observations. These demonstrate the potential of precise geodetic survey techniques for constant monitoring and risk assessment of heavy industrial complexes against seismic hazards by ongoing fault activities. differential interferometric SAR; time series analysis; surface deformation; GPS; earthquake 2019 11 1199 11101199 11.11101199 11.11101199 11.11101199 11.11101199 11.1101199 11.11101199 11.1101199 11.11101199 11.1101199 11. Korea, where the target area of this study is located, has previously been considered relatively safe from seismic hazards owing to an absence of major active tectonics. However, two recent earthquakes, the 2016 Gyeongju (magnitude 5.8, depth of epicenter 15.2 km) event [5; 6; 7] and the 2017 Pohang (magnitude 5.4, depth of epicenter 6.9 km) earthquake event [8; 9], have aroused national concern about the safety of residential, industrial, and social infrastructure. Before the 1990s, Korea did not have any regulations on earthquake resistant construction design; given the growing population and development of industry and infrastructure, this could trigger socio-economically disastrous events, the so-called domino effect [10]. The south-eastern part of the Korean Peninsula is the densest industrial hub equipped with chemical, heavy machinery, and atomic power planets; incidentally, in close proximity with the epicenters of the two recent earthquakes. Although the magnitude of two earthquakes were below generally accepted critical values (magnitude 6.5 to 7.0) for significant structural damage, the city of Ulsan fell under public scrutiny because of its high concentration of transportation networks for chemical agents, heavy production facilities, and high population density. There is concern for the safety of the city from coseismic, postseismic, and even preseismic surface motion, based on historical cases [11; 12; 13; 14]. A major concern is the vulnerability of industrial pipelines filled with toxic and combustible liquid materials [15; 16]; note that earthquakes are responsible for 5% of all incidents of poisonous chemical material exposure [17; 18]. In addition, direct damage from earthquakes include the impacts of liquefaction, which could result in serious damage to sensitive industrial facilities. Hence, a series of studies are being conducted to assist with the preemptive design of facilities and postinvestigation methods [19; 20; 21]. In the case of Ulsan, in addition to government bodies initiating a sequence of ground surveys for safety checks over major facilities, a geodetic campaign employing space borne assets and a GPS network was proposed to address the complexity and extent of the target area.