L o n g - t e r m g r o u n d w a t e r l e v - PowerPoint PPT Presentation

L o n g - t e r m g r o u n d w a t e r l e v e l c h a n g e s o n t h e f o c a l r e g i o n o f t h e 1 9 9 9 C h i - C h i e a r t h q u a k e , T a i w a n ○ N a o j iK o i z u m i ( G e o l o g i c a l S u r v e y o f J a p a n , A I S T ] , W e n - C h i L a i , C h j e n g - L u nS h i e h ( D i s a s t e r P r e v e n t i o n R e s e a r c h C e n t e r , N C K U ) K u o - C h y n gC h a n g ( W a t e r R e s o u r c e A g e n c y , T a i w a n ) T o s h i h a r u Y a m a d a ( K a t s u j i m aC o . L t d . )

1 9 9 9C H I - C H I E A R T H Q U A K E : M w 7 . 6 T I M E : 1 : 4 7 O N S E P 2 1 , 1 9 9 9 （L O C A L T I M E ） D E P T H : 6 ｋｍ S H A L L O W E A R T H Q U A K E I N T H E P L A T E B O U N D A R Y M A X I M U M S E I S M I C I N T E N S I T Y : 6 O R G R E A T E R I N J M A S C A L E D E A D > 2 , 3 0 0

Program for Earthquakes and Program for Earthquakes and Active- -fault Research (PEAR) fault Research (PEAR) Active 2001-2005 • Seismogenic-zone structures • Earthquake geology • Seismicity and seismotectonics • Crustal deformations • Earthquake physics (including physics, chemistry,rock mechanics, and hydrology related to earthquakes ) • Strong-motion seismology and DPRC,WRA engineering seismology (GSJ) 2006 ～

OBSERVATION WELLS OF WRA N U M B E R > 5 5 0 R E S O L U T I O N : 1 - ２ｃｍ U N I F O R M I N V E S T I G A T I O N O F H Y D R O - G E O L O G I C A L S T R U C T U R E 1 S T A T I O N H A S 2 O R 3 W E L L S . O N E I S S H A L L O W ( 5 - 3 0 M ) T H E O T H E R S A R E D E E P ( 1 0 0 - 3 0 0 M ) . ★ ・P U M P I N G E F F E C T I S L A R G E . ・N O N - U N I F O R M D I S T R I B U T I O N F O C A L R E G I O N 6 6 S T A T I O N S 1 6 8 W E L L S D E P T H : 1 5 ｍ～3 0 6 ｍ

ON AND AROUND FOCAL REGION OF THE 1999 CHI-CHI ERTHQUAKE SLOPE OR ALLUVIAL FAN S E I S M I C MOUNTAIN I N T E N S I T Y ( J M A S C A L E ) 4 ～6 CALUCULATED FROM SEISMIC ACCELERATION DATA USING KAWASUMI’S FORMULA Wen-Chi Lai et.al(2004)

AQUIFERS Altitude(m) Altitude(m) A A' 100 100 UNCONFINED ！ Upper Fan Lower Fan Middle Fan 50 50 0 0 Layer 1 -50 -50 Layer 2-1 -100 -100 Layer 2-2 -150 -150 Layer 3 -200 -200 -250 -250 Layer 4 -300 -300 Gravel Sand -350 -350 Silt and Mud (Aquitard) 0 5 10 15 Km H ： V ＝ 1 ： 100 Wen-Chi Lai et.al

N O . O F C O S E I S M I C P E R C A N T A G E A Q U I F E R S I T U A T I O N W E L L S C H A N G E S ( % ) L A Y E R 1 U N C O N F I N E D 3 9 7 1 8 L A Y E R 2 ( 1 + 2 ) C O N F I N E D 7 8 4 3 5 5 L A Y E R 3 C O N F I N E D 3 8 2 8 7 4 L A Y E R 4 C O N F I N E D 1 3 9 6 9 A L L 1 6 8 8 7 5 2

EARTHQUAKE FAULT East Weat Earthquake Fault 8 8 8 COSEISMIC WATER LEVEL CHANGE (m) S L O P E , M O U N T A I N ALLUVIAL FAN 4 4 4 0 0 0 Water Level Changes (m) Water Level Change (m) 4 -4 -4 Legend Layer 1 Layer 2-1 Layer 2-2 8 -8 -8 Layer 3 Layer 4 -12 -12 60000 50000 40000 30000 20000 10000 0 West 60 40 20 0 East Distance of Earthquake Fault (m) DISTANCE FROM EARTHQUAKE FAULT ( km)

S L O P E , M O U N T A I N 200 West 200 ALLUVIAL FAN East Earthquake Fault ALTITUDE OF WATER TABLE (m) DROP BY 150 PERMEABILITY ENHANCEMENT Altitude of water table (m) 100 RISE BY 100 LIQUEFACTION 50 0 0 SEA LEVEL PUMPING -50 -50 60000 40000 20000 0 West 60 40 20 0 East Distance between observation wells and the earthquake fault (m) DISTANCE FROM EARTHQUAKE FAULT ( km) V/H ～ 250

MAIN FACTORS FOR EARTHQUAKE-RELATED GROUNDWATER CHANGES Lee et al.(2002) VOLUMETRC SEISMIC GROUND MOTION STRAIN CHANGE Koizumi PERMEABILITY LIQUEFACTION et al.(2004) CHANGE Wang et al. (2001) Lai et al.(2004)

20 NO COSEISMIC CHAGE SMALL COSEISMIC CHANGE COUNT LARGE COSEISMIC CHANGE 10 NO RECOVERY 0 0 100 200 A C C E L E R A T I O N ( g a l ）

Layer-1 （ UNCONFINED AQUIFER) NO COSEISMIC CHAGE 5 SMALL COSEISMIC CHANGE LARGE COSEISMIC CHANGE COUNT 0 0 100 200 A C C E L E R A T I O N ( g a l ）

Layer2 （ CONFINED AQUIFER ） 10 NO COSEISMIC CHAGE SMALL COSEISMIC CHANGE LARGE COSEISMIC CHANGE COUNT 0 0 100 200 A C C E L E R A T I O N ( g a l ）

D A I L Y V A L U E ( 1 9 9 3 - 2 0 0 0 ) 2 0 ｍ 1 Y E A R 1 日値の変化

2 0 ｍ

EPICENTER DROP RISE

S L O P E , M O U N T A I N 200 West 200 ALLUVIAL FAN East Earthquake Fault ALTITUDE OF WATER TABLE (m) DROP BY 150 PERMEABILITY ENHANCEMENT Altitude of water table (m) 100 RISE BY 100 LIQUEFACTION GROUND SURFACE B O U N D A R Y C O N D I T I O N 50 W A S N O T C H A N G E D P E R M E A B I L I T Y W A S 0 I N I T I A L L Y L A R G E . 0 SEA LEVEL V.D.< 0.2m L O C A L P R E S S U R E C H A N G E PUMPING W A S D I M I N I S H E D -50 -50 60000 40000 20000 0 West 60 40 20 0 East Distance between observation wells and the earthquake fault (m) DISTANCE FROM EARTHQUAKE FAULT ( km) V/H ～ 250

C O N C L U S I O N S ・W e i n v e s t i g a t e d w a t e r l e v e l c h a n g e s i n t h e 6 6 s t a t i o n s ( 1 6 8 w e l l s ) o n a n d a r o u n d t h e f o c a l r e g i o n o f t h e 1 9 9 9 C h i - C h i e a r t h q u a k ed u r i n g t h e p e r i o d f r o m 1 9 9 3 t o 2 0 0 0 . T h e d e p t h s o f t h e w e l l s r a n g e b e t w e e n 1 5 m a n d 3 0 6 m . ・M o s t o f t h e w e l l w a t e r l e v e l s w h i c h c h a n g e d c o s e i s m i c a l l y r e c o v e r e d b y D e c e m b e r 2 0 0 0 . A l l o f t h e w e l l w a t e r l e v e l s i n t h e a l l u v i a l f a n r e c o v e r d . ・3 w e l l w a t e r l e v e l s , w h i c h d r o p p e d c o s e i s m i c a l l yb y p e r m e a b i l i t y e n h a n c e m e n t , d i d n o t r e c o v e r . T h e y a r e s i t u a t e d i n t h e s l o p e o r m o u n t a i n z o n e s n e a r t h e e a r t h q u a k e f a u l t . ・T h e p o s s i b l e r e a s o n s a r e a s f o l l o w s ; ( 1 ) P e r m e a b i l i t i e so f t h e a q u i f e r s i n t h e a l l u v i a l f a n a r e o r i g i n a l l yl a r g e , ( 2 ) L e v e l s o f n e i g h b o r i n g s e a , r i v e r s a n d l a k e s o r p o n d s , w h i c h a r e i m p o r t a n t b o u n d a r y c o n d i t i o n s c o n t r o l l i n g g r o u n d w a t e r p r e s s u r e s , d i d n o t l a r g e l y c h a n g e a f t e r t h e 1 9 9 9 C h i - C h i e a r t h q u a k e .

N O . O F C O S E I S M I C P E R C A N T A G E A Q U I F E R S I T U A T I O N W E L L S C H A N G E S ( % ) L A Y E R 1 U N C O N F I N E D 3 9 7 1 8 L A Y E R 2 ( 1 + 2 ) C O N F I N E D 7 8 4 3 5 5 L A Y E R 3 C O N F I N E D 3 8 2 8 7 4 L A Y E R 4 C O N F I N E D 1 3 9 6 9 A L L 1 6 8 8 7 5 2

Spatial distribution (P.G.A. and Vol. strain) • PGA H • Volumetric strain 2700000 # # # # # # # # # # # # # # # 1100 # # # # 2650000 # # # # # # # # # # # # 1000 # # # # # # # # # # # 900 # # # # # # # # # # # # # # # # # # # # # 800 # # # # # # # # # # # # # # # 700 # # # # # # # # # # # # # # # # # # # # # # # # # # # 600 # # # # # # # # # # # # # # # 2600000 # # # # # # # 500 # # # # # # # # # # # # # # # # # # 400 # # # # # # # # 300 # # # 200 100 0 2550000 2500000 Vol. strain (ppm) 150000 200000 250000