Stress drop variations among small earthquakes before the 2011 Tohoku‐oki, Japan, earthquake and implications for the main shock

摘要: It is important to assess the likely rupture characteristics of future megathrust earthquakes. One approach study spatiotemporal variation geophysical properties in active subduction zones. We explore this idea by examining stress drops 1563 small earthquakes (Mw 3.0–4.5) shallower than 80 km Tohoku-oki region before 2011 earthquake. Although individual drop estimates exhibit considerable scatter, we find a strong increase with depth between 30 km and 60 km, whereas for deeper events, respectively, are nearly constant. also identify lateral variations along strike. Higher-than-average found East Aomori-oki Miyagi-oki, Sanriku-oki moderate area. The high zone Miyagi-oki located just south large slip area earthquake, possibly acted as barrier further propagation during event. In addition, frequency dependence seismic radiation observed main shock, proportionally higher frequencies coming from parts fault, mimics see same region. These results imply that smaller pre-main shock can provide insight into fault consequent processes