Along‐dip variation in seismic radiation of the 2011 Ibaraki‐oki, Japan, earthquake ( M w 7.9) inferred using a multiple‐period‐band source inversion approach

Abstract

To elucidate the spatial variation in period‐dependent seismic radiation for the 2011 Ibaraki‐oki earthquake (Mw 7.9) in Japan, we applied a multiple‐period‐band source inversion approach to near‐source strong‐motion waveforms of this earthquake. We estimated source models of this earthquake in three successive period bands (5–10, 10–25, and 25–50 s) using strong‐motion data and Green's functions based on a 3‐D velocity structure model. The source models in the period bands of 10–25 and 25–50 s had large slips in the area to the south and southeast of the hypocenter in the depth range of 23–35 km, while the large slip area for the source model in the period band of 5–10 s was located in the deeper region ~30 km west of the hypocenter in the depth range of 35–45 km. These results indicate that long‐period (10–25 and 25–50 s) and short‐period (5–10 s) seismic waves were predominantly radiated from these different regions along the dip direction during the 2011 Ibaraki‐oki earthquake. This along‐dip variation in the dominant period of seismic radiation can be explained by the variation in scale in unstable sliding patches according to depth.