fractal distribution of induced seismicity in masjed soleyman dam site (south west of iran)

Authors

محمدرضا ابراهیمی

دانشجوی دکتری زلزله شناسی، پژوهشگاه بین المللی زلزله شناسی و مهندسی زلزله، تهران، ایران محمد تاتار

دانشیار، پژوهشگاه بین المللی زلزله شناسی و مهندسی زلزله، تهران، ایران

abstract

masjed soleyman dam site is located in the zagros mountain of western iran, which is one of the most seismically active zones of the alpe-himalayan belt. after impounding of dam, the seismicity of area increased considerably, showing the impact of reservoir (177 m height, 261 million m3) in changing the rate of seismicity in the area. we have analyzed the seismicity of area in terms of the spatial variation of fractal dimension and have compared it with the frequency-magnitude relation b-value. in the mid-2006, a digital seismograph network of five medium-band stations consist of trillium-40t, 40 sec-50 hz seismometer connected to 24 bit nonometric taurus recorder was established around the axis and reservoir of the masjed soleyman dam site by international institute of earthquake engineering and seismology (iiees). the earthquake catalog of masjed soleyman network since june 1, 2006 to october 1, 2007 contains 3609 well-located events. as the epicenter of induced earthquakes are mostly within the 30 kilometers radius of dam and their hypocenter is located at depth less than 20 kilometers, therefore we selected only 1924 events which satisfied above selection criteria. during monitoring period, two large earthquakes with magnitude of 3.9 and 3.6 struck the area on november 23, 2006 and september 1, 2007, respectively. these earthquakes happened following a rapid change in water level of reservoir. the phenomenon such as earthquakes and faults are self-similar systems at any scale and can be described by a power-law relation. the exponent of this relation that shows the degree of complexity in a chaotic system is called the fractal dimension. although the term of fractals was introduced to the world by mandelbort in 1967, power-law relations in order to investigate the geophysical phenomena were used earlier. gutenberg and richter defined a relationship between the frequencies and magnitudes of earthquakes in 1945. the slop of the plot of occurrence numbers against magnitudes is known as the b-value and has been used as the indicator of seismic activity of the studied region. in this study we try to understand the loading impact due to reservoir water impoundment on both d and b-value parameters. we used correlation dimension which is the most commonly method for calculation the fractal dimension of earthquake hypocenter. to map the variation of fractal dimension as a function of space, the entire area was set into 0.05° × 0.05° grids. an overlapping of 25% is made for a comprehensive picture of the map. the 23 grids were created interactively, and the region with events less than 40 did not used in this estimation. the number of events in each grid varied from 40 to 109. in this exercise, the fractal dimension value ranged from 0.40 to 0.93, but the values were less than 1. the number of earthquakes, n with magnitude greater than mc is related to the magnitude by logn=a?bm, which is widely known as the gutenberg–richter relation. in this study, the b-value of the gutenberg–richter relation was estimated by a maximum likelihood method which is claimed to be a better estimation. the threshold magnitude of 0.9 has been found for the dam region by examining the log-linear plot of cumulative number of events versus magnitude. we have obtained that b-value in the area varies from 0.6–1.3. the low d value obtained here may have several explanations. seismic activity in the masjed soleyman reservoir site occurs in a small area, and the distances between mainshocks and aftershocks are very small (sometimes less than 3 km) which may result in a low d value. if we consider that the seismicity of the masjed soleyman region is due to the fault interactions and reservoir-triggered forces which generate earthquakes in small clusters, since our data are in protracted step of seismicity in the area and the main factors for occurrence of earthquakes in this step are seepage of fluid in the crust and increase in pore pressure diffusion, therefore high permeability and presence of fluids in the fault and surrounding area may reduce effective stresses and show relatively low d. the low d value could also be the effect of high pore fluid pressure in the region as pore fluid pressure reflects redistribution of stress in the substratum. when d tends to zero, the seismicity of the area may not be due to any particular fault but may be connected to the stress generated by high pore fluid pressure; this indicates the point source zone. having high b-value in the studied region especially in the vicinity of dam indicates heterogeneous stress distribution in the crust whereas homogeneous stresses results in lower b-values. gradual increase in pore pressure is the main factor in occurrence of induced earthquakes, whereas this increase could be the result of faults weakening due to pore pressure diffusion, therefore we could see a heterogeneous stress distribution in the area and high b-values. so the lower d values (d ? 0.6) and higher b-values (b ? 0.8) in some grids indicate that there is a heterogeneous structure in this area and it seems that dam region is susceptible for occurrence of induced earthquakes. the results show a desirable correlation between d and b-value that indicates on existing of induced seismicity in area. the impact of increasing pure fluid pressure on both parameters (fractal dimension d and b-value) is truly observable for this area.

Upgrade to premium to download articles

Sign up to access the full text

Already have an account?login

similar resources

Preliminary evaluation of induced seismicity at the Karkheh dam site in southwest Iran

The reservoir-induced seismicity (RIS) at the Karkheh dam site with a reservoir capacity of about 7.4x109 meters is investigated. Based on the assessment of the seismicity of the dam site in equal time periods before and after reservoir impoundment, it was found that the number of earthquakes have been tripled after impoundment, while their magnitudes and focal depths become smaller. The averag...

full text

Assessment of reservoir sedimentation by mathematical model GSTARS3 on Masjed Soleyman dam in Khuzestan Province-Iran

Accumulation of sediment transport volume and reduce the useful life of dams, water storage tanks can be. So far, many methods for calculating sediment this is presented in reservoirs are generally classified into two categories: mathematical modeling and experimental .This study examines the effect of using Gstars model parameters in the model, deposition of sediment in the reservoir tank and ...

full text

Statistical Evaluation of Induced Seismicity at the Karkheh Dam, Iran

Karkheh Dam is the largest dam in Iran with a capacity of about 7.4×109 cubic meters and height of 127 meters. Since the first impoundment, increasing in seismic activity in the dam area has been observed that indicates the possible occurrence of reservoir-induced seismicity (RIS).In the present work, a preliminary evaluation is conducted firstly in order to investigate these observations. Base...

full text

analyzing patterns of classroom interaction in efl classrooms in iran

با به کار گیری روش گفتما ن شنا سی در تحقیق حا ضر گفتا ر میا ن آموزگا را ن و زبا ن آموزا ن در کلا سهای زبا ن انگلیسی در ایرا ن مورد بررسی قرار گرفت. ا هداف تحقیق عبا رت بودند از: الف) شنا سا ئی سا ختارهای ارتبا ط گفتا ری میا ن معلمین و زبا ن آموزا ن ب) بررسی تا ثیر نقش جنسیت دبیرا ن و زبا ن آموزان بر سا ختا رهای ارتبا ط گفتا ری میا ن آنها پ) مشخص کردن اینکه آ یا آموزگاران غا لب بر این ارتبا ط گف...

numerical stady of pore pressure development and dissipation in core of masjed-soleyman rockfill dam

the main role ofcore in earth dams is to reduce and control the seepage flow through the dam. in order to achieve this purpose, the core material is usually selected from pure or mixed clays.due to very small coefficient of permeability, the clay cores can prevent water leakageeasily. however, pore water pressures developed inside the core during construction, can not be dissipated quickly. as ...

full text

the impact of e-readiness on ec success in public sector in iran the impact of e-readiness on ec success in public sector in iran

acknowledge the importance of e-commerce to their countries and to survival of their businesses and in creating and encouraging an atmosphere for the wide adoption and success of e-commerce in the long term. the investment for implementing e-commerce in the public sector is one of the areas which is focused in government‘s action plan for cross-disciplinary it development and e-readiness in go...

My Resources

Save resource for easier access later


Journal title:
فیزیک زمین و فضا

جلد ۳۸، شماره ۲، صفحات ۱۵-۲۷

Keywords
[ ' m a s j e d s o l e y m a n d a m s i t e i s l o c a t e d i n t h e z a g r o s m o u n t a i n o f w e s t e r n i r a n ' , ' w h i c h i s o n e o f t h e m o s t s e i s m i c a l l y a c t i v e z o n e s o f t h e a l p e ' , ' h i m a l a y a n b e l t . a f t e r i m p o u n d i n g o f d a m ' , ' t h e s e i s m i c i t y o f a r e a i n c r e a s e d c o n s i d e r a b l y ' , ' s h o w i n g t h e i m p a c t o f r e s e r v o i r ( 1 7 7 m h e i g h t ' , ' 2 6 1 m i l l i o n m 3 ) i n c h a n g i n g t h e r a t e o f s e i s m i c i t y i n t h e a r e a . w e h a v e a n a l y z e d t h e s e i s m i c i t y o f a r e a i n t e r m s o f t h e s p a t i a l v a r i a t i o n o f f r a c t a l d i m e n s i o n a n d h a v e c o m p a r e d i t w i t h t h e f r e q u e n c y ' , ' m a g n i t u d e r e l a t i o n b ' , ' v a l u e . i n t h e m i d ' , 2 0 0 6 , ' a d i g i t a l s e i s m o g r a p h n e t w o r k o f f i v e m e d i u m ' , ' b a n d s t a t i o n s c o n s i s t o f t r i l l i u m ' , ' 4 0 t ' , ' 4 0 s e c ' , ' 5 0 h z s e i s m o m e t e r c o n n e c t e d t o 2 4 b i t n o n o m e t r i c t a u r u s r e c o r d e r w a s e s t a b l i s h e d a r o u n d t h e a x i s a n d r e s e r v o i r o f t h e m a s j e d s o l e y m a n d a m s i t e b y i n t e r n a t i o n a l i n s t i t u t e o f e a r t h q u a k e e n g i n e e r i n g a n d s e i s m o l o g y ( i i e e s ) . t h e e a r t h q u a k e c a t a l o g o f m a s j e d s o l e y m a n n e t w o r k s i n c e j u n e 1 ' , ' 2 0 0 6 t o o c t o b e r 1 ' , ' 2 0 0 7 c o n t a i n s 3 6 0 9 w e l l ' , ' l o c a t e d e v e n t s . a s t h e e p i c e n t e r o f i n d u c e d e a r t h q u a k e s a r e m o s t l y w i t h i n t h e 3 0 k i l o m e t e r s r a d i u s o f d a m a n d t h e i r h y p o c e n t e r i s l o c a t e d a t d e p t h l e s s t h a n 2 0 k i l o m e t e r s ' , ' t h e r e f o r e w e s e l e c t e d o n l y 1 9 2 4 e v e n t s w h i c h s a t i s f i e d a b o v e s e l e c t i o n c r i t e r i a . d u r i n g m o n i t o r i n g p e r i o d ' , ' t w o l a r g e e a r t h q u a k e s w i t h m a g n i t u d e o f 3 . 9 a n d 3 . 6 s t r u c k t h e a r e a o n n o v e m b e r 2 3 ' , ' 2 0 0 6 a n d s e p t e m b e r 1 ' , 2 0 0 7 , ' r e s p e c t i v e l y . t h e s e e a r t h q u a k e s h a p p e n e d f o l l o w i n g a r a p i d c h a n g e i n w a t e r l e v e l o f r e s e r v o i r . t h e p h e n o m e n o n s u c h a s e a r t h q u a k e s a n d f a u l t s a r e s e l f ' , ' s i m i l a r s y s t e m s a t a n y s c a l e a n d c a n b e d e s c r i b e d b y a p o w e r ' , ' l a w r e l a t i o n . t h e e x p o n e n t o f t h i s r e l a t i o n t h a t s h o w s t h e d e g r e e o f c o m p l e x i t y i n a c h a o t i c s y s t e m i s c a l l e d t h e f r a c t a l d i m e n s i o n . a l t h o u g h t h e t e r m o f f r a c t a l s w a s i n t r o d u c e d t o t h e w o r l d b y m a n d e l b o r t i n 1 9 6 7 ' , ' p o w e r ' , ' l a w r e l a t i o n s i n o r d e r t o i n v e s t i g a t e t h e g e o p h y s i c a l p h e n o m e n a w e r e u s e d e a r l i e r . r n g u t e n b e r g a n d r i c h t e r d e f i n e d a r e l a t i o n s h i p b e t w e e n t h e f r e q u e n c i e s a n d m a g n i t u d e s o f e a r t h q u a k e s i n 1 9 4 5 . t h e s l o p o f t h e p l o t o f o c c u r r e n c e n u m b e r s a g a i n s t m a g n i t u d e s i s k n o w n a s t h e b ' , ' v a l u e a n d h a s b e e n u s e d a s t h e i n d i c a t o r o f s e i s m i c a c t i v i t y o f t h e s t u d i e d r e g i o n . i n t h i s s t u d y w e t r y t o u n d e r s t a n d t h e l o a d i n g i m p a c t d u e t o r e s e r v o i r w a t e r i m p o u n d m e n t o n b o t h d a n d b ' , ' v a l u e p a r a m e t e r s . w e u s e d c o r r e l a t i o n d i m e n s i o n w h i c h i s t h e m o s t c o m m o n l y m e t h o d f o r c a l c u l a t i o n t h e f r a c t a l d i m e n s i o n o f e a r t h q u a k e h y p o c e n t e r . t o m a p t h e v a r i a t i o n o f f r a c t a l d i m e n s i o n a s a f u n c t i o n o f s p a c e ' , ' t h e e n t i r e a r e a w a s s e t i n t o 0 . 0 5 ° × 0 . 0 5 ° g r i d s . a n o v e r l a p p i n g o f 2 5 % i s m a d e f o r a c o m p r e h e n s i v e p i c t u r e o f t h e m a p . t h e 2 3 g r i d s w e r e c r e a t e d i n t e r a c t i v e l y ' , ' a n d t h e r e g i o n w i t h e v e n t s l e s s t h a n 4 0 d i d n o t u s e d i n t h i s e s t i m a t i o n . t h e n u m b e r o f e v e n t s i n e a c h g r i d v a r i e d f r o m 4 0 t o 1 0 9 . i n t h i s e x e r c i s e ' , ' t h e f r a c t a l d i m e n s i o n v a l u e r a n g e d f r o m 0 . 4 0 t o 0 . 9 3 ' , ' b u t t h e v a l u e s w e r e l e s s t h a n 1 . t h e n u m b e r o f e a r t h q u a k e s ' , ' n w i t h m a g n i t u d e g r e a t e r t h a n m c i s r e l a t e d t o t h e m a g n i t u d e b y l o g n = a ? b m ' , ' w h i c h i s w i d e l y k n o w n a s t h e g u t e n b e r g – r i c h t e r r e l a t i o n . i n t h i s s t u d y ' , ' t h e b ' , ' v a l u e o f t h e g u t e n b e r g – r i c h t e r r e l a t i o n w a s e s t i m a t e d b y a m a x i m u m l i k e l i h o o d m e t h o d w h i c h i s c l a i m e d t o b e a b e t t e r e s t i m a t i o n . t h e t h r e s h o l d m a g n i t u d e o f 0 . 9 h a s b e e n f o u n d f o r t h e d a m r e g i o n b y e x a m i n i n g t h e l o g ' , ' l i n e a r p l o t o f c u m u l a t i v e n u m b e r o f e v e n t s v e r s u s m a g n i t u d e . w e h a v e o b t a i n e d t h a t b ' , ' v a l u e i n t h e a r e a v a r i e s f r o m 0 . 6 – 1 . 3 . t h e l o w d v a l u e o b t a i n e d h e r e m a y h a v e s e v e r a l e x p l a n a t i o n s . r n s e i s m i c a c t i v i t y i n t h e m a s j e d s o l e y m a n r e s e r v o i r s i t e o c c u r s i n a s m a l l a r e a ' , ' a n d t h e d i s t a n c e s b e t w e e n m a i n s h o c k s a n d a f t e r s h o c k s a r e v e r y s m a l l ( s o m e t i m e s l e s s t h a n 3 k m ) w h i c h m a y r e s u l t i n a l o w d v a l u e . i f w e c o n s i d e r t h a t t h e s e i s m i c i t y o f t h e m a s j e d s o l e y m a n r e g i o n i s d u e t o t h e f a u l t i n t e r a c t i o n s a n d r e s e r v o i r ' , ' t r i g g e r e d f o r c e s w h i c h g e n e r a t e e a r t h q u a k e s i n s m a l l c l u s t e r s ' , ' s i n c e o u r d a t a a r e i n p r o t r a c t e d s t e p o f s e i s m i c i t y i n t h e a r e a a n d t h e m a i n f a c t o r s f o r o c c u r r e n c e o f e a r t h q u a k e s i n t h i s s t e p a r e s e e p a g e o f f l u i d i n t h e c r u s t a n d i n c r e a s e i n p o r e p r e s s u r e d i f f u s i o n ' , ' t h e r e f o r e h i g h p e r m e a b i l i t y a n d p r e s e n c e o f f l u i d s i n t h e f a u l t a n d s u r r o u n d i n g a r e a m a y r e d u c e e f f e c t i v e s t r e s s e s a n d s h o w r e l a t i v e l y l o w d . t h e l o w d v a l u e c o u l d a l s o b e t h e e f f e c t o f h i g h p o r e f l u i d p r e s s u r e i n t h e r e g i o n a s p o r e f l u i d p r e s s u r e r e f l e c t s r e d i s t r i b u t i o n o f s t r e s s i n t h e s u b s t r a t u m . w h e n d t e n d s t o z e r o ' , ' t h e s e i s m i c i t y o f t h e a r e a m a y n o t b e d u e t o a n y p a r t i c u l a r f a u l t b u t m a y b e c o n n e c t e d t o t h e s t r e s s g e n e r a t e d b y h i g h p o r e f l u i d p r e s s u r e ; t h i s i n d i c a t e s t h e p o i n t s o u r c e z o n e . h a v i n g h i g h b ' , ' v a l u e i n t h e s t u d i e d r e g i o n e s p e c i a l l y i n t h e v i c i n i t y o f d a m i n d i c a t e s h e t e r o g e n e o u s s t r e s s d i s t r i b u t i o n i n t h e c r u s t w h e r e a s h o m o g e n e o u s s t r e s s e s r e s u l t s i n l o w e r b ' , ' v a l u e s . g r a d u a l i n c r e a s e i n p o r e p r e s s u r e i s t h e m a i n f a c t o r i n o c c u r r e n c e o f i n d u c e d e a r t h q u a k e s ' , ' w h e r e a s t h i s i n c r e a s e c o u l d b e t h e r e s u l t o f f a u l t s w e a k e n i n g d u e t o p o r e p r e s s u r e d i f f u s i o n ' , ' t h e r e f o r e w e c o u l d s e e a h e t e r o g e n e o u s s t r e s s d i s t r i b u t i o n i n t h e a r e a a n d h i g h b ' , ' v a l u e s . s o t h e l o w e r d v a l u e s ( d ? 0 . 6 ) a n d h i g h e r b ' , ' v a l u e s ( b ? 0 . 8 ) i n s o m e g r i d s i n d i c a t e t h a t t h e r e i s a h e t e r o g e n e o u s s t r u c t u r e i n t h i s a r e a a n d i t s e e m s t h a t d a m r e g i o n i s s u s c e p t i b l e f o r o c c u r r e n c e o f i n d u c e d e a r t h q u a k e s . t h e r e s u l t s s h o w a d e s i r a b l e c o r r e l a t i o n b e t w e e n d a n d b ' , ' v a l u e t h a t i n d i c a t e s o n e x i s t i n g o f i n d u c e d s e i s m i c i t y i n a r e a . t h e i m p a c t o f i n c r e a s i n g p u r e f l u i d p r e s s u r e o n b o t h p a r a m e t e r s ( f r a c t a l d i m e n s i o n d a n d b ' , ' v a l u e ) i s t r u l y o b s e r v a b l e f o r t h i s a r e a . ' ]

Hosted on Doprax cloud platform doprax.com

copyright © 2015-2023