Detailed Session Information

Session 4.2:

Physical scale dependencies, observed scaling relations and simulation

Convenors: M. Ohnaka (Japan), B. Shaw (USA)


Session Overview: Miti Ohnaka (15 minutes)

We are primarily concerned with physical modeling/simulation of a large 
earthquake, and eventual modeling for earthquake prediction, for which 
scale dependency of earthquake rupture is of critical importance. It is 
widely recognized that the size of an earthquake and some physical 
quantities inherent in the rupture are scale-dependent. Earlier studies 
show that these scale dependencies are closely related to 
geometric/structural properties of the seismogenic layer and the fault 
zone. Since the scale dependency is a key to quantitative 
modeIing/simulation of the earthquake generation process, 
this is crucial to be addressed:
  1. How are scale-dependent physical quantities scaled in terms of the underlying physics ?
  2. How are earthquakes prescribed by geometric/structural properties of the seismogenic zone and the fault zone ?
  3. How are large earthquakes distinguished from small earthquakes ?
  4. What are the central observations a realistic model would have to match?
  5. What is the relative importance of fixed heterogeneities, like material and geometrical ones, versus dynamic heterogeneities like stress? How do they interact?

1. How are scale-dependent physical quantities scaled in terms of the underlying physics ?

Understanding of how the earthquake rupture that proceeds in a tectonic 
setting is scaled in terms of the underlying physics is a key to 
quantitative modeling/simulation of the earthquake generation process. 
Hence, how scale-dependent physical quantities are scaled in terms of 
the underlying physics will be explored.

2. How are earthquakes prescribed by geometric/structural properties of the seismogenic zone and the fault zone ?

The seismogenic layer and the fault zone include characteristic lengths 
of various scales departed from the self-similarity. The depth of 
seismogenic layer, fault segment size, fault zone thickness, barrier or 
asperity size will be representative examples of such characteristic 
scales. How the size of an earthquake is virtually prescribed by these 
characteristic scales in a given tectonic setting will be explored.

3. How are large earthquakes distinguished from small earthquakes ?

A large earthquake occurs along a preexisting fault of large-scale. An 
inhomogeneous fault evolves gradually with the repetition of earthquake 
slip on the fault ina given tectonic setting, and this will make a 
matured fault depart from the self-similarity. A large earthquake tends 
to occur along such a matured, large-scale fault. In addition, a large 
earthquake can take place, only after a large amount of the elastic 
strain energy has been stored in the medium surrounding the fault. 
Unless an enough amount of the strain energy has been stored in the 
medium surrounding a fault, a large earthquake cannot be induced along 
the fault by stress transfer due to fault-fault interaction. Oncea large 
earthquake occurs, a long time period will be needed for the amount of 
strain energy to reach once again a critical level which has a potential 
to produce anext large earthquake on the same fault. This is contrasted 
with the case for a small earthquake, because the amount of the strain 
energy needed for a small earthquake to occur may reach instantly to the 
critical level by dynamic stress transfer. These suggest that large 
earthquakes may be distinguished from small earthquakes. This will be 
explored.

Two additional questions will also be posed:

4. What are the central observations a realistic model would have to match?

5. What is the relative importance of fixed heterogeneities, like material and geometrical ones, versus dynamic heterogeneities like stress? How do they interact?


Session Plenary: (1 Hour)

Keiiti Aki (20 minutes)
Scale dependence in earthquake processes and seismogenic structures

Mitiyasu Ohnaka (20 minutes)
A unified comprehension for fracture of intact rock, frictional slip 
failure, and earthquake rupture, and scaling of scale-dependent physical 
quantities inherent in the rupture.

Bruce Shaw (20 minutes)
Constraining the physics of earthquakes with observations

Detailed Session: (2.5 Hours)

1. How are scale-dependent physical quantities scaled in terms of the
underlying physics ?

J. H. Dieterich (20 minutes)
Earthquake nucleation and its relationship to earthquake clustering

2.How are earthquakes prescribed by geometric/structural properties of 
the seismogenic zone and the fault zone ?

Y. Fujii and M. Matsuura (20 minutes)
Regional difference in scaling laws for large earthquakes 
and its tectonic implication

3.How large earthquakes are distinguished from small earthquakes ?

L. Knopoff and M.W. Lee (20 minutes)
The self-organization of aftershocks

Discussion and Comments (90 minutes)