Mhendislik Bilimlerinde zel KonularMUB9035 - Mhendislik Bilimleri Blmstanbul niversitesi

MUB9035*

displacement rateAlmost 1000 stations in Japanese Islands daily measurement of location with accuracy of 1[cm] GPS Earth Observation Network (GEONET)

Aftershocks of July 26, 2003 (Mw=6.0)GPS-local stations

Strain rates (Aydan, 2002, 2003)

Average Strain Rates computed by using 1st-order derivative from displacementsCoordinate system and the definition of displacement rates for a triangular elementDisplacementsStrain ratesStrain rates

25.ttf

stress rate tensor computed by using Hookes law from the computed strain rates for elastic materials.

Maximum Shear Stress + * Mean Stress Rate Disturbing Stress Rate= Friction of coefficient ( =0.8)Lames Constants 30 GPa [Fowler, 1990] Strain rates

Disturbing stress changes and asperity

Over the full range: A significant positive correlation is observed between seismic clustering (D) and the Gutenberg-Richter b value along the NAFZ strike slip zone.

Over the 10 -40 km scale: A nearly significant relationship between b and D is observed (r = 0.74, p = 0.06) and suggests that the relationship is primarily associated with deeper or regional scale seismicity since significant correlation is not observed over the 2 to 10 km scale.

No correlation was observed between seismicity ( b, D2, D15) and GPS strain.

Correlation between seismicity and GPS strain

Sheet1

D2D15bShearDilatD2D15bShearDilatD2D15bShearDilat

D20.970.81-0.290.280.5-0.39-0.490.490.960.74-0.2597308490.0806374249

D1500.75-0.380.310.25-0.4-0.390.6500.77-0.28024623620.2254765284

b0.030.05-0.1-0.060.390.37-0.1-0.060.060.05-0.1-0.06

Shear0.520.40.83-0.790.260.390.83-0.790.570.540.83-0.79

Dilat0.550.50.90.030.260.120.90.030.860.630.90.03

Sheet2

Sheet3

No correlation was observed between b, D2, D15, and GPS strain.

Afterthoughts on the Izmit EarthquakeIncreased b and decreased DC suggest that the rise in the level of low magnitude seismicity and high intensity clustering along the western portion of NAFZ did not completely release stress transferred into this segment of the fault zone (Oncel et al., 1995, Non.Lineer.Geophysics; Oncel and Wilson, 2001, BSSA).This combination of factors - westward migration along with increased levels of low magnitude seismicity and higher intensity seismic clustering - are indicators of increased seismic risk in the area.

Positive Correlation

Negative Correlation

Low-magnitude events

(Preshocks)

Large-magnitude events

Over the 2-10 km scale: Significant correlation is not observed between seismic clustering and dilatation.

Over the full range: Significant correlation between b and D is not observed.

Over the 10 -40 km scale: In this subdivision, seismic clustering (D2 and D15) correlate positively with dilatation (r = 0.67 and 0.73 with p = 0.02 and 0.01 respectively). The correlations suggest that increased rates of extension produce increasingly dispersed seismicity.

Correlation between seismicity and GPS strain

Sheet1

D2D15bShearDilatD2D15bShearDilatD2D15bShearDilat

D20.98-0.290.180.40.48-0.130.180.20.9800.130.67

D150-0.380.180.460.120.280.31-0.440-0.050.150.73

b0.360.230.180.210.690.380.180.2110.880.180.21

Shear0.570.590.570.130.570.340.570.130.680.650.570.13

Dilat0.190.130.510.670.540.150.510.670.020.010.510.67

Sheet2

Sheet3

One would expect seismicity to correlate moreso with dilatation in a subduction zone. However, dilatation along the subduction zone is on average only slightly negative. Dilatation is positive in the areas to the northeast (17 nstrain/a) and negative (-29 nstrain/a) farther west along the subduction zone. This combination of positive and negative dilatation along the subduction zone is probably responsible for the lack of a more significant correlation between b and dilatation. The change of dilatation from positive to negative as one goes east to west along the subduction zone suggests a transition in plate interaction from transtensional to transpressive.

Over the full range: Variations of b value correlate negatively with shear (r = -0.83, p = 0.04) in the zones of this subdivision. The correlation of b to dilatation is weakly positive (r = 0.73, p = 0.1).

Correlation between seismicity and GPS strain

Sheet1

D2D15bShearDilatD2D15bShearDilatD2D15bShearDilat

D20.760.51-0.250.030.210.44-0.540.380.90.22-0.2195451992-0.4054407334

D150.080.71-0.680.470.69-0.020.260.460.010.39-0.44-0.1

b0.30.12-0.830.730.380.97-0.830.730.680.45-0.830.73

Shear0.640.140.04-0.60.260.620.04-0.60.680.390.04-0.6

Dilat0.960.340.10.210.460.370.10.210.430.840.10.21

Sheet2

Sheet3

MUB9035*No correlation was observed between b, D2, D15, and GPS strain.