5 FIG. 4: The difference (in percent) of survival probabilities between cases without and with an anomalous accumulation of electrons eval- uated in the perturbation theory Eq. (14). 1500 1525 1550 1575 1600 1625 1650 1675 L GLYPH<LParen1> km GLYPH<RParen1> 0 0.5 1 1.5 2 2.5 3 GLYPH<CapDelta> P GLYPH<LParen1> Ν GLYPH<OverBar> GLYPH<Minus>GLYPH<Greater>Ν GLYPH<OverBar> GLYPH<RParen1>GLYPH<LParen1> % GLYPH<RParen1> and the plus and minus signs correspond to antineutrinos and neutrinos, respectively. By the formula for flavor-to-flavo r transition, we obtain the survival probability of the electron antineutrino originating from the initial spot x$_{0}$ and ending at the final spot x$_{f}$ . Up to the leading order of V ( x ) , we have In this scheme, we calculate the survival probability for re- actor electron antineutrinos. The result is shown in Fig. 4. The difference in survival probabilities for the cases with and without the anomalous electron accumulation can be as large as 3 % , which is larger than the results obtained with the R - matrix method. Discussion.— We note that there is a sharp controversy about the η value among geologists. Some think that this value should be rather small, whereas others advocate that, before a severe earthquake, the η might reach a sizable value. Taking the advice of the more conservative geologists, we adopt a rel- atively small value in this work. Indeed, we only investigate the physics and provide a possible way to forecast the earth- quake in terms of neutrino medium effects in this work, but we will leave the detailed study of the η value to the geologists. In fact, the other neutrino sources, such as the cosmic muon, would contaminate our detection circumstance. How- ever, we may set some shielding and veto facilities to reduce the uncertainty caused by other neutrino sources. The detailed technical difficulties would be left for our experimental co l- leagues. Foreseeing earthquakes in a certain region within ten years, two years and one or two months corresponds to long-, medium- and short-term earthquake forecast, while an im- pending earthquake forecast should be made a few days be- fore the outbreak. For the long-term and medium-term fore- cast, there is quite a long duration for the detector to collect sufficient data even though the flux is suppressed by the small A scheme might remedy the shortcoming of remarkably losing neutrino flux due to the small solid angle. Namely, one may use a low energy beta beam [25] as a source. Such a neutrino beam could be directly oriented to the fault zone. Without the 10 − 5 suppression factor, the requirement for the size and sensitivity of the detectors would be greatly allevi- ated. However, in order to obtain intense and collimated neu- trino beams from the traditional source for the beta beam, e.g., Indeed, in our present work, we consider idealized beam characteristics while ignoring many details. The uncertainty caused by other neutrino sources such as other reactors and geoneutrinos, is also ignored, which may be one of the main challenges in the implementation of this scheme. Thus we reach our conclusion that with the present reactor facilities and detection techniques, it is still a difficult task to make an earthquake forecast using such a scheme, though it seems to be possible from a theoretical point of view while ignor- ing some uncertainties. However, there is hope that with the great improvement in detection and innovation of facilities, the sensitivity and efficiency would be greatly improved and the size of the detector may be much larger with sufficient fund support, and with the development of the geology and seismology, the pictures of the fault zone will be clearer and its parameters more accurate, thus a medium-term earthquake forecast would be feasible. Now let us make a rough numerical evaluation of the event rates based on the Daya Bay Monte-Carlo simulation. In the Daya Bay case, the detector is set at 1 km away from the neu- trino source, and the detection rate is about a few hundred per day ( ∼ 400/day, as estimated). Supposing a shortened base- line in our case is 200km, the suppression factor for the flux would be 1 / (200) 2 ∼ 3 × 10 − $^{5}$. Considering an exposure time of 100 days and assuming that the detection efficiency is 100 times larger than that employed in Daya Bay experiment, the expected events would be at least O (100), which is suit- able for a medium-term forecast. For example, in a period of one year, one can compare the events observed in the first half of the year with that in the second half. If these data show an explicit difference in survival probabilities during the two periods, they would imply a geological deformation that may result in an earthquake in the forthcoming period. The closer the earthquake is, the larger the difference. solid angle spanned by the detector. For short-term and im- pending forecasting, the electron density changes drastically as the earthquake is coming, and the overall effect results in a large shift in the oscillation probability in a short time inter- val, so that observing clear signals might be feasible if the flux from the source is sufficiently strong. As mentioned previ- ously, the geometrical deformation caused by strain and shear would last for a long period, say, hundreds of years in some cases and the deformation would eventually reach its maxi- mum before the outbreak. However, the strong anomalous electric field appears only several days, e.g. about a week before the earthquake, so that the week before the outbreak is crucial for detectors to collect data and reach a conclusion about the upcoming disaster. P$_{¯}$ ν$_{e}$ → ¯ ν$_{e}$ = 1 − sin $^{2}$2 θ$_{0}$ [ sin 2 1 2 φ m x $_{0}$→ x$_{f}$ − √$_{2}$ 4 cos 2 θ$_{0}$ × ∫ x$_{f}$ x 0 dx G$_{F}$ ρ ( x ) m$_{N}$ ( sin φ m x $_{0}$→ x + sin φ m x → x$_{f}$ ) ] . (14)