Spatially Spatially smoothed seismicity approachsmoothed seismicity approach

NATO Science for Peace and Security Programme, Sfp Project 983054 (BSHAP)“Harmonization of Seismic Hazard Maps for the Western Balkan Countries ”

http://www.wbseismicmaps.org/

Spatially smoothed seismicity approach (As the detailed knowledge of seismotectonics is not available at the moment)

Using OHAZ (Computer program for Seismic Hazard Calculations, developed by ARSO (Slovenia) and ISA (Albania))

- Based on Frankel’s aproach (Frankel, 1995.)- Seismic source zones ↔ grid cells- Circular Gaussian smoothing of activity rate

PSHA Methodology

- Improved by ARSO (Lapajne et al., 1997, 2003; Lapajne 2000, Sket Motnikar et al., 2000, Poljak et al., 2000) : Energy models of activity rate, ...

Common Earthquake Catalogue “BSHAP Catalogue”

- National catalogues needed to be merged, homogenized, declustered, completed, .. . (Herak, 2010)

PSHA Evaluation

Seismic activity, Annual rates, Ground motions

- Seismic activity obtained from an Earthquake Catalogue as counted seismicity (grid cells), normalization performed using standard Gutenberg-Richter relationship, smoothing performed by using Spatially smoothed approach (due to uncertainity of the epicentral location) –> circular smoothing of seismic activity by (circular) Gausian function with radius (3 correlation distance) that equals max estimated error in epicentral location

PSHA Evaluation

PGM models

In this study, different Predictive Ground Motion models (attenuation models) were used

- Ambraseys et al., 2005, Horizontal peak ground acceleration:

lnY=b0+b1M+(b2+b3M)ln(r+r0)+f(S)+f(F)

with Soil condition:

f(S)=bSB*SB+bSC*SC+bSD*SD

PSHA Evaluation

- Sabetta & Pugliese, 1996, Horizontal peak ground acceleration:

lnY=b0+b1M+b2ln(r+r0)+f(S)+f(F)

with Soil condition:

f(S)=bSB*SB+bSC*SC+bSD*SD

and their combinations, with different weights.

PSHA Evaluation

Ohaz interface with input parameters for Hazard calculation

PSHA Evaluation

- Hazard was calculated for different starting magnitudes, finally M=4 was adopted as final value. Guttenberg-Richter b value was also modified, and calculated within program as well. Variations were from b= 0.6 to b=0.9 (Reference: Herak, BSHAP meeting in Banja Luka; b= 0.55 –0.85 for the most of Croatia)

- But, ... do we have enough earthquakes ?- Aki (1965) indicate that a minimum of 2000 earthquakes are needed to calculate b to within 0.05 at 98% confidence ...

- What about spatial variations of b ?

PSHA Evaluation

- Catalogue completeness • One of the most important things in this approach• Small variations of starting year -> respectable

differences in resulting PGA values• 1650, 1750, 1850?

PSHA Evaluation

In the calculations, G-R recurrence relationship was used in doubly-truncated exponential form (to confine the range of magnitudes)

Annual rates of exceeding ground motion were computed for given Reference ground motion levels:

0.005 0.010 0.050 0.100 0.120 0.140 0.160 0.180 0.200 0.220 0.240 0.260 0.280 0.300 0.350 0.400 0.450 0.500 0.600 0.700 0.800 0.900 1.00

PSHA Results

- Final ground motions are calculated for different return periods, 475 and 1000 years

- Calculations were performed for time period from 1650.

- Peak Ground Acceleration (see next slide) for given return period of 475 years, in terms of g

- b value was taken as 0.85- Magnitude was bounded between 4.0 and 8.0,

starting magnitude 4.0, normalizing factor 1.00, and max distance 100 km

- Calculations were performed for the Site Category A (Hard Rock)

PSHA Results

PGA (475 y)in terms of g

PSHA Conclusions

Spatial distribution of PGA values coincides with expected hazard values, according to the distribution of epicenters

PSHA Results

Maximum PGA is obtained for Metkovic area (South Croatia) and wider Southern Dalmatia

PGA MAX = 0.428 g

Wider Zagreb area and Dubrovnik area

PGA ZAG = 0.390 g PGA DUB = 0.369 g

For comparison model, next slide shows PGA for Europe (SESAME Project, 2003)

PSHA Results

European-Mediterranean Seismic Hazard Map (SESAME 2003)

PGA values for southern Croatiaand wider Zagreb area arearound 0.35 g

PSHA Conclusions

There is a good coincidence between PGA maps, presenting completely different methods and input parameters, both in spatial distribution and maximal accelerations

Spatially smoothed Spatially smoothed seismicityseismicity approach provides approach provides respectablerespectable results, results, butbut ......very sensitive very sensitive to input parameters (catalogue to input parameters (catalogue completeness, ...) completeness, ...)

More complex More complex model should be used model should be used (Containing (Containing seismotectonicsseismotectonics, seismic , seismic zonationzonation, , etc...) etc...) to compare resultsto compare results

PSHA Conclusions

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