Stress information needed for various geological engineering projects is normally restricted at relatively shallow depths (less than a few km range). Since the shallow stress state may be perturbed by several known effects, not necessarily represented by tectonic stress field at tens of km seismogenic depth, it is often difficult to characterize representative shallow stress states. We compile hundreds of hydraulic fracturing stress measurement data (World Stress Map quality ranking range of B-E) and analyze them statistically to characterize the stress orientations in Korea. The area of the country is divided by several regularly spaced bins of 0.25° in longitude and latitude. Representative stress orientations in individual bins are calculated using different statistical approaches depending on data quality, number of data, and range of uniform stress orientation in and around individual bins. Different approaches yield distinct stress orientations, suggesting that the choice of the method utilized to characterize stress orientation is critical. We propose a technique optimized for relatively low-quality data to best characterize the stress orientation. The resulting stress orientations are generally consistent with deeper tectonic stress field, suggesting that even the shallow stresses largely reflect deep crustal stress state. In some locations, however, shallow stresses deviate quite consistently from the deep tectonic stress field, emphasizing a systematic influence of near-surface process on shallow stress field.

1. Introduction

There is an increasing demand for investigating stress states in shallow crust for energy resource development and underground space utilization. Recent examples are development of geothermal energy and shale gas, CO2 geological storage, and construction of nuclear waste repository. Target depths in such projects ranges typically from a few hundred m to a few km. In all these projects, information of in situ stress field is crucial to understand the site characteristics and various geomechanical problems associated with the operation of the projects.

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