2 FIG. 1: The configuration of the trajectory of the (anti)neut rino beam which is produced in the source S , propagates through slabs I , II and III , and reaches the detector D . The baseline length L = L I + w + L III . The geometry of the fault zone is described by three parameters, length l , depth d and width w . The matter density of each slab is also marked in the figure. ηρ 0 L I , ρ 0 I II III L III , ρ 0 L = L I + w + L III l d w S D zone is composed of three parallel faults. The Wenchuan- Maoxian fault is the west most one. According to geological studies, the Longmenshan fault zone is stressed by the west Bayan Har Block and Sichuan Basin [12], and a 300 km long and 50 km wide deformation zone was formed horizontally. The simplified geometric structure of the fault zone, which we are going to use in this work, is a cuboid with length l = 300 km, width w = 50 km and depth d = 10 km, and with an upper edge parallel to the earth’s surface. In general, a crust extends to a depth of 30 km [13], and this cuboid is just located at its middle layer. The main shock of the Wenchuan earthquake has a hypocenter depth of about 14 km, and this hypocenter is inside the cuboid. A schematic of the cuboid is shown in Fig. 1. The geological structure with a fault zone is not stable and sometimes varies actively. The drastic variations within the region of such geological structure can induce severe earth- quakes. Before an earthquake takes place, the variation in the matter density, or more exactly, the electron density of the fault zone is the most significant factor. The relevant effec ts are categorized into four aspects: • Strain . Strain can change the matter density directly. During the Wenchuan earthquake, the Longmenshan fault zone is strained by the west and east geological blocks. The map of strain intensity drawn by a pro- fessional research group [14] shows that the eastern edge of the Qinghai-Xizang Plateau is close to the re- gion where strain intensity changes steeply. The Long- menshan fault zone undergoes the steepest change. The strain intensity on the west side is four times larger than that on the east side. • Shear . Shear plays an important role in the slippage of the fault. It can either increase or decrease the matter density. From the maximum shear strain rate map of the Bayan Har Block and Sichuan Basin [12], one can ob- serve that the maximum shear strain rate of the east of the Longmenshan fault zone is 5 × 10 − $^{9}$/a , whereas on the west side, Bayan Har Block, it is 15 ∼ 50 × 10 − $^{9}$/a . The picture indicates that the shear contrast of both sides is 3 ∼ 10. • Anomalous electric field . The total electron content • Rock dehydration . Under the influence of tremendous strain and shear, rock would undergo a dehydration pro- cess, which also contributes to the density shift in the fault zone [18]. (TEC) anomaly, as one of the precursors of an earth- quake, has been observed from the TEC map using the GPS satellites. The authors of Ref. [15] point out that, for strong mid-latitudinal earthquakes, the seismo- ionospheric anomalies are manifested as a local TEC increase or decrease in the vicinity of the forthcom- ing earthquake epicenter, and this phenomenon appears several days prior to the main shock and the TEC mod- ification can be as large as 30 ∼ 90 % of the normal value. The physical mechanism for such ionospheric anomalies is that an anomalous electric field is pro- duced near the epicenter. Prior to an earthquake, inten- sive gas discharges occurring at the crust in the earth- quake preparation zone lead to an anomalously strong vertical electric field [16]. The TEC disturbances are the vertical drift of the ionospheric plasma under the in- fluence of the anomalous electric field. On the other hand, if the anomalous vertical electric field definitely exerts influence on the earthquake preparation zone, it can also change the distribution of free electrons in the fault zone. In particular, the research into conductiv- ity characteristics indicates that a low resistance thrust fault zone in the middle layer of the Longmenshan fault zone was observed [17]. The first two aspects concern the geometrical deforma- tion, which contributes an accumulation of mechanical en- ergy. When the shear exceeded the friction strength, the faults in the fault zone were unlocked and slipped suddenly [19]. Density shift and estimation of fault zone width.— As an- tineutrinos travel inside the medium, the matter potential V ( x ) is linearly proportional to the electron density. For the medium in the crust, it is reasonable to assume that N$_{e}$ ≈ N$_{p}$ ≈ N$_{n}$ , i.e. the electron fraction number Y$_{e}$ = N$_{e}$/ ( N$_{p}$ + N$_{n}$ ) 0.5, where N$_{e}$ , N$_{p}$ and N$_{n}$ correspond to electron, proton and neutron numbers in the crust layer, and write the electron density in the normal crust matter as where ρ$_{0}$ is the matter density of the normal medium and m$_{N}$ is the mass of nucleon. As discussed above, the electron den- sity is shifted in the fault zone as As pre-earthquake activities in the fault zone are taken into account, ρ varies from ρ$_{0}$ into an effective matter density ρ ′ f which means that in the fault zone the effective matter den- sity shortly before an earthquake, ρ ′ $_{f}$, is η times larger than n 0 $_{e}$( x ) = ρ$_{0}$ ( x ) 2 m$_{N}$ , (3) n f e = ηn 0 $_{e}$. (4) ρ ′ f = ηρ$_{0}$, (5)