Nonsystematic Rupture Directivity of Geothermal Energy Induced Microseismicity in Helsinki, Finland

Abstract The rupture behavior of microseismicity in fluid‐injection settings with low fault stresses is generally believed to be controlled by the pore pressure, including a tendency larger induced earthquakes into perturbed volume toward injection well, implying degree predictability. Here, we examine directivity patterns identify planes and directions 21 largest (local magnitudes, 1.3–1.9) recorded during 2018 St1 Deep Heat geothermal project near Helsinki, Finland. We use Empirical Green's Function technique retrieve per‐seismic‐station corner frequencies, earthquake durations, trends. After combining trends focal mechanisms calculated using principle component analysis, resolve 10 events. In contrast studies events at other sites, find that one event toward, two away, remaining parallel well. Furthermore, prefer mode II failures rather than III. These observations provide new constraints for mechanical models growth pore‐pressure dominated settings.