Field Detection of Microcracks to Define the Nucleation Stage of Earthquake Occurrence

Abstract

Main shocks of natural earthquakes are known to be accompanied by preshocks which evolve following the modified Ohmori’s law in average over many samples. Individual preshock activity, however, is far less systematic for predictive purposes. On the other hand, the microcracks in laboratory rock experiments are always preceded to final rupture. And, previous investigations of field acoustic emissions showed that the activity increases prominently before and after the main shock. But there is no detection of any phenomena to identify the nucleation stage. Here we show that a special underground electric field measurement could detect microcracks. Pulse-like variations were classified into three groups (A, B, C) by frequency. The B-type is suggested to define the nucleation period: activity increases sharply following the modified Omori’s law before the main shock and there is no activity afterward. The B-type is subgrouped into three types possibly corresponding to crack-rupture modes. The variations are supposed to be induced by crack occurrence through electrokinetic effects in the elastic-porous medium. The detection distance is suggested to be several orders larger than that of the acoustic emission due to the effective smallness of dissipation rate, and the waveform can be used to infer the rupture mode.

Assessing the Potential Earthquake Precursory Information in ULF Magnetic Data Recorded in Kanto, Japan during 2000–2010: Distance and Magnitude Dependences

“…The measurement of ultra-low-frequency (ULF: less than one Hertz) electromagnetic phenomena may be one of the most promising candidates, because of their deeper skin depths [ 1 , 2 , 8 , 17 ]. To date, a large number of ULF electromagnetic phenomena associated with earthquakes has been reported from different parts of the world, e.g., Greece [ 18 , 19 , 20 , 21 , 22 , 23 ], Italy [ 24 , 25 ], Russia [ 26 , 27 ]; America [ 28 , 29 , 30 ], Mexico [ 31 , 32 , 33 , 34 ], Taiwan [ 35 , 36 , 37 , 38 ], Indonesia [ 39 , 40 ], China [ 41 , 42 , 43 , 44 , 45 , 46 , 47 ] and Japan [ 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 ]. Furthermore, experiments and simulations have confirmed the existence of ULF seismo-electromagnetic phenomena [ 61 , 62 , 63 , 64 , ...…”

Progress of Applied Seismo-Electromagnetism

“…Our new observation, which started on March 3, 2011 at Hasaki (now Kamisu City, Ibaraki Prefecture) enabled us to investigate particular co-rupture signals using an updated dynamic range. We could detect very interesting electric variations, suggested to be induced by microcracks in the nucleation stage of earthquakes [8].…”

A Practical Method for Short-term Earthquake Prediction Using Multiple High-frequency Tremor Events

“…These phenomena have been used for long-term and short-term predictions. Kato et al [13] found, for instance, two sequences of slow slip events migrating towards the mainshock rupture initiation point before the 2011 Tohoku earthquake, but no direct results led to practical short-term prediction methods.…”