Direct magnetic signals from earthquake rupturing: Iwate-Miyagi earthquake of M 7.2, Japan

► We first successfully observed “co-rupturing” Earth's magnetic field changes. ► Observed co-rupturing geomagnetic field changes are due to the piezomagnetic effect. ► We made a comparative evaluation between the observed values and calculated ones. ► The observed changes can be well interpreted in terms of the piezomagnetic effect. ► Our results indicate the feasibility of fastest emergency earthquake warning system.