Mühendislik Bilimlerinde Özel

Konular

MUBİ9035 - Mühendislik Bilimleri Bölümüİstanbul Üniversitesi

displacement rate

Almost 1000 stations in Japanese Islands daily measurement of location with accuracy of 1[cm]

1 3 0 Ê 1 4 0 Ê3 0 Ê

4 0 Ê

GPS Earth Observation Network (GEONET)

WAKUYA

OSHIKA

ONAGAWA

RIFU

MIYAGITAIWA

140.9 141 141.1 141.2 141.3 141.4 141.5

38.2

38.3

38.4

38.5

38.67.5 km

Mw=6.0, 2003/07/26 07:13Mw=5.2, 2003/07/26 16:56

Mw=5.3, 2003/07/25 00:13GPS Stations

Aftershocks of M>1.7July 26-September 22

YAMOTO

SHIKAMA

0 2 4 6 8 10 12 14

-15

-10

-5

0

Dep

th [k

m]

Distance [km]

B B'

0 5 10 15 20

-15

-10

-5

0

Dep

th [k

m]

Distance [km]

A A'

Aftershocks of July 26, 2003 (Mw=6.0)

GPS-local stations

Strain rates (Aydan, 2002, 2003)

xu

xx

yv

yy

yu

xv

xy

uv xx yy

x

y

O

Uii

j

k

U j

U k

Vk

V j

Vi

Average Strain Rates computed by using 1st-order

derivative from displacements

Coordinate system and the definition of displacement rates for a triangular element

Displacements

Strain rates

Strain rates

stress rate tensor computed by using Hooke’s law from the computed strain rates for elastic materials.

xy

yy

xx

xy

yy

xx

000202

231

max

Maximum Shear Stress + * Mean Stress Rate

231

m

Disturbing Stress Rate=

Friction of coefficient ( =0.8)

Lame’s Constants ≈ 30 GPa [Fowler, 1990]

Strain rates

md max

2002 2003 2004

0

1

2

0

10

20

30

40

TIME (Julian)DIS

TURB

ING

STR

ESS

RATE

(MPa

)

DISTURBING STRESS RATE

Miy -Wak-Yam Osh-Ona-Yam Osh-Rif -Yam Rif -Miy -Yam Wak-Ona-Yam

MRI

M6.2

M7.0

MRI

=M*1

00/R

=0.8 WAKUYA

OSHIKA

ONAGAWA

RIFU

MIYAGITAIWA

140.9 141 141.1 141.2 141.3 141.4 141.5

38.2

38.3

38.4

38.5

38.67.5 km

Mw=6.0, 2003/07/26 07:13Mw=5.2, 2003/07/26 16:56

Mw=5.3, 2003/07/25 00:13GPS Stations

Aftershocks of M>1.7July 26-September 22

YAMOTO

SHIKAMA

Disturbing stress changes and asperity

D2 D15 b Shear Dilat D2 D15 b Shear Dilat D2 D15 b Shear DilatD2 0.97 0.81 -0.29 0.28 0.5 -0.39 -0.49 0.49 0.96 0.74 -0.26 0.08D15 0 0.75 -0.38 0.31 0.25 -0.4 -0.39 0.65 0 0.77 -0.28 0.23b 0.03 0.05 -0.1 -0.06 0.39 0.37 -0.1 -0.06 0.06 0.05 -0.1 -0.06Shear 0.52 0.4 0.83 -0.79 0.26 0.39 0.83 -0.79 0.57 0.54 0.83 -0.79Dilat 0.55 0.5 0.9 0.03 0.26 0.12 0.9 0.03 0.86 0.63 0.9 0.03

•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

PositiveCorrelation

NegativeCorrelation

Low-magnitude events(Preshocks)

Large-magnitude events

Afterthoughts on the Izmit Earthquake

Increased 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.

D2 D15 b Shear Dilat D2 D15 b Shear Dilat D2 D15 b Shear DilatD2 0.98 -0.29 0.18 0.4 0.48 -0.13 0.18 0.2 0.98 0 0.13 0.67D15 0 -0.38 0.18 0.46 0.12 0.28 0.31 -0.44 0 -0.05 0.15 0.73b 0.36 0.23 0.18 0.21 0.69 0.38 0.18 0.21 1 0.88 0.18 0.21Shear 0.57 0.59 0.57 0.13 0.57 0.34 0.57 0.13 0.68 0.65 0.57 0.13Dilat 0.19 0.13 0.51 0.67 0.54 0.15 0.51 0.67 0.02 0.01 0.51 0.67

•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

D2 D15 b Shear Dilat D2 D15 b Shear Dilat D2 D15 b Shear DilatD2 0.76 0.51 -0.25 0.03 0.21 0.44 -0.54 0.38 0.9 0.22 -0.22 -0.41D15 0.08 0.71 -0.68 0.47 0.69 -0.02 0.26 0.46 0.01 0.39 -0.44 -0.1b 0.3 0.12 -0.83 0.73 0.38 0.97 -0.83 0.73 0.68 0.45 -0.83 0.73Shear 0.64 0.14 0.04 -0.6 0.26 0.62 0.04 -0.6 0.68 0.39 0.04 -0.6Dilat 0.96 0.34 0.1 0.21 0.46 0.37 0.1 0.21 0.43 0.84 0.1 0.21

•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