Physical Models
Physical models are more extrapolated approach on particular region and they are not
depending on the exact seismogenic mechanism, taking place in that region. No single
Physical models can be used to identify all three parameters required for successful
prediction. Different physical models are to be used for identifying different parameters of
impending earthquakes.
Tidal Model triggering big earthquakes
The Earth-tides mechanism was first known as a prospective trigger for the
occurrence of devastating earthquakes. This approach helps us to study the time of
occurrence of earthquakes in correlation to Earth-tides.
Tidal forces distort bodies experiencing differential gravitational forces. This
generally occurs for bodies of finite range in gravitational fields, since gravitational forces
are inversely proportional to the square of the distance, according to Newton’s Law of
Gravitation. Thus, lunar gravity disturbs the solid part of the earth, but tides in the solid part
of the earth are smaller compared to that of tides in the ocean.
Mutual induction of tides in the solid part of the Earth and the Moon leads to a
complicated coupling of the rotational and orbital motions of the two objects. These tidal
forces and associated couplings have the following general effects:
The interior of the Earth and Moon are heated by the tides in their bodies, just as a
paper clip is heated by constant bending. This effect is very small for the Earth and Moon,
but it can be dramatic for other objects that experience much larger differential gravitational
forces and, therefore, much larger tidal forces. For example, the tidal forces exerted by
Jupiter on its moon Io are so large that the solid surface of Io is raised and lowered by
hundreds of meters twice in each rotational period. This motion so heats the interior of Io
that it is probably mostly molten; as a consequence, Io is covered with active volcanoes and
is the geologically most active object in the Solar System. The heat source that produces
volcanic activity on Earth is the energy released from the decay of radioactive materials
within the interior, as well as from heat left over from Earth's formation. But tidal heating
produced by Jupiter and the other Galilean satellites is responsible for the massive volcanism
on Io.
From this one can infer that when the peak amplitude of lithosphere oscillation super
impose with stress load of the plate developed due to its motion, the particular region can go
above critical stress level, which can trigger an earthquake. Therefore, devastating
earthquake can occur whenever tidal peak values elevate region’s stress level beyond critical
level the big earthquakes will get triggered. Tidal model can effectively be used to resolve in
finding the time of occurrence of big events.
Homogenous Earth Model
This model assumes the earth as a homogenous one and the earth’s physical
properties are not location dependent. This assumption is made specifically to understand the
electrical signal generation characteristics of the seismogenic region. Since the earth is
considered as isotropic medium, the equipotential surfaces can be drawn. Electrical signal
originated from the strained rocks radially in outward direction with equipotential are
orthogonal to the signal propagation lines. This model is useful in identifying most probable
area among a seismogenic region, where an impending earthquake is approaching after
making necessary correction for regional geological conditions.
Energy Flow Model
Due to the plate motion, there continuous energy input into the lithosphere. The
energy stored in the lithosphere is released in the form of small magnitude tremors. From the
analysis of given time gap (normally in gap will be in years), the normal seismicity can be
identified. Any deviation from the normal seismicity (increase or decrease) for a given time
gap is signpost for strong impending earthquake. The lithosphere is either in a state of critical
dynamic equilibrium or in the stage of unstable position, with no critical length scale when it
pertains to inflow and out flow of strain energy.
On the basis of law of conservation of energy, an open physical system under
dynamic equilibrium condition the input energy is directly proportional to output energy. The
normal output energy can be derived from the analysis of paleo seismic records. When this
equilibrium get disturbed, the energy is stored and the physical system would burst at any
moment by releasing stored energy. This disturbance might be either caused by frictional or
by mechanical means along the fault segment. The period of deviation from the normal
seismicity is called as “locking period”. The magnitude of the impending earthquake can be
calculated from the difference between the energy levels corresponding to beginning and end
of the lock period. The physical model is more useful in deciding the magnitude of the big
impending earthquakes.
Stress Transfer Model
Moderate to large earthquakes can induce the location and time of occurrence of
future earthquakes due to the static stress transfer. Coseismic and post – seismic stress
changes are settled onto the faults in the region and onto the fault planes of subsequent
earthquakes. Coseismic stress calculations can be done by considering the Earth as a
homogenous elastic half space and faults as rectangular dislocations surrounded within it and
post seismic stress change calculations are done using stratified earth model. Coulomb failure
function is used to evaluate whether the fault or rupture plane of expected event brought
closer or away from the failure due to the previous earthquakes. Positive changes in coulomb
stress indicate faults are brought close to failure.