|
A California earthquake forecast, the 2008 ''Uniform California Earthquake Rupture Forecast, Version 2'' (UCERF 2), has been prepared by the ''Working Group on California Earthquake Probabilities'' (WGCEP).〔WGCEP is a collaboration of the U.S. Geological Survey, the California Geological Survey, and the Southern California Earthquake Center).〕 Of the hundreds of seismogenic (earthquake causing) geologic faults in California,〔See USGS QFFDB.〕 UCERF classifies only six faults as Type A sources, meaning there is sufficient information to both estimate and model the probability of a Magnitude (M) 6.7 or greater earthquake within 30 years.〔.〕 These six faults (summarized in Table A, below) are the: (1) San Andreas (split into northern and southern sections, (2) San Jacinto, (3) Elsinore, (4) Garlock, (5) Calaveras, and (6) Hayward-Rodgers Creek.〔, and Table 12〕 Faults which are known to be slipping (and therefore seismogenic) but lack sufficient information to fully model how close they might be to rupture are classified as Type B. About twenty of these faults (see Table B) are estimated to have a 5% or greater chance of an M ≥ 6.7 earthquake within 30 years.〔, p. 74.〕 An additional six areas where strain is accumulating but where knowledge is insufficient to apportion slip onto specific faults are classified as Type C sources.〔.〕 There is additional chance of earthquakes on faults that were not modeled, and of lesser earthquakes. Northern California has an estimated 12% chance over the same 30 years of an M ≥ 8 megathrust earthquake on the Cascadia subduction zone.〔, p.75.〕 UCERF has also prepared "participation probability maps" 〔, p. 79.〕 of the chance that any area will experience an earthquake above a certain magnitude from any source in the next 30 years (see figure). == Methodology == UCERF probabilities of an earthquake on a given fault are based on four layers of modeling:〔UCERF, pp. 12-13, and fig. 3.〕 # A ''fault model'' of the fault's physical geometry. # A ''deformation model'' of slip rates and related factors for each fault section. # An ''earthquake rate model'' of the region. # A ''probability model'' for estimating probability of an earthquake during a specified interval. These are used to produce both ''time-independent'' and ''time-dependent'' forecasts of earthquake probabilities. The former are based on "stress-renewal" models of seismic stress being released by an earthquake, then renewing (or rebounding; see Elastic-rebound theory) until it triggers another earthquake. In time-dependent models the probability of a fault rupturing thus depends on how long stress has been accumulating since the last rupture. However, the details of how this happens are not adequately known, so time-dependent methods estimate the periodicity and currently accumulated strain based on observed seismicity. Out of this a time-independent earthquake rate model (ERM) is produced, from which the time-dependent probability model (UCERF) is derived.〔UCERF, p. 12.〕 (For more information see "Can earthquakes be predicted?" in the External links.) It should be noted that the concept of stress-renewal has been criticized, and may even be invalid,〔See Kagan, 1997, esp. §3.3.3.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「California earthquake forecast」の詳細全文を読む スポンサード リンク
|