Seismic Hazard Assessment of Switzerland, Falko Bethmann October 1 st, 2008

Transcription

1 Seismic Hazard Assessment of Switzerland, 2004 Falko Bethmann October 1 st, 2008

2 Outline Definition of earthquake sources Definition of seismic recurrence characteristics for each source Ground motion model including ground motion variability Hazard spectra for different probabilities of exceedance and development of hazard curves De-aggregation of hazard to develop controlling scenario events defined by magnitude distance pairs Work flow for a modern PSHA study following the Cornell-McGuire model

3 Definition of earthquake sources Historical observation Paleoseismic observation Instrumental observation Earthquake catalog Recurrence parameters (completeness) Declustering

4 Swiss historical record

5 Basel, October 18,1356

6 Macroseismic Record 1855, M6.4, Visp 1356, M6.9, Basel

7 Reinach fault: westward view

8 Reinach fault: trench view

9 Paleoseismology on the Reinach fault

10 Earthquake record in Swiss lakes

11 Drilling lake sediments

12 Details from lake Seewen cores tilted, disrupted and deformed layers sand injection sand dyke

13 Correlating events Ba 00-3 waterdepth 65m 0 Ba 97-3 waterdepth 60m 0 65 cal y BP Ba 00-4 waterdepth 57m 0 S Cal y AD/BC Cal y BP 2000 AD 0 (1950 AD) Lake Lungern Lake Seelisberg Lake Lucerne (Schnellmann et al. 2002) Lake Baldegg Core Core Core Core Seismic Seismic Seismic Seismic E1 C e n t r a l S w i t z e r l a n d N E1 (1601?) 500 cal y BP? 1601 AD Lucerne 1356 AD Basle E2 E1 E1 E2 500 cal y BP? AD cal y BP? cal y BP? E E2 (1356?) 1000 cal y BP? cal y BP? 1500 cal y BP cal y BP cal y BP 2000 cal y BP 3000 cal y BP 4000 cal y BP 1000 BC E3 E4? Uncertain dating E2 E4 E cal y BP cal y BP E cal y BP 6000 cal y BP cal y BP E cal y BP E E cal y BP cal y BP cal y BP cal y BP cal y BP 4000 cal y BP cal y BP 4 E E4 Uncertain dating cal y BP C Si S cal y BP cal y BP Facies E cal y BP Faintly laminated carbonate mud with gravels Carbonate mud E7 Faintly laminated carbonate mud Well laminated carbonate mud E cal y BP 7000 cal y BP cal y BP Biochemical varves Turbidites thicker than 2 mm cal y BP cal y BP Ba 97-5 waterdepth 58m cal y BP Deformations Artificial deformation Weak deformation E1 Clear deformation, event horizon E cal y BP cal y BP Mean value of 2 sigma range of calibrated 14C ages cal y BP C Si S 9000 cal y BP VKT?, cal y BP C Si S cal y BP E cal y BP cal y BP cal y BP LST, cal y BP cal y BP Slump deposit Mud extrusion? Liquefaction structure Disturbed lamination Clearly non-seismic event Possible seismic event Probable seismic event cal y BP C Si S 4 holes in Lake Baldegg 4 lakes in C. Switzerland

14 Paleoseismology, slumps in Lake Lucerne

15 Dating rockfalls in the Basel area

16 Dating rockfalls in the Basel area

17 Dating collapses in caves

18 Earthquakes in Switzerland Macroseismic Instrumental

19 High-precision earthquake location

20 Seismic strain and stress

21 Switzerland Activity rates Basel area

22 Seismic source zones and Mmax

23 weak-motion attenuation Weak-motion attenuation

24 SED attenuation model

25 Uncertainty in strong-ground motions

26 The process of hazard computing Montecarlo simulation approach - Create a synthetic catalog of earthquakes - Spans 1 million years, magnitude >4, -> 2 million events - Depth is given - Alternative models and their weighting are considered by creating subcatalogs - This procedure is repeated for all nodes evenly spaced on a 5 x 5 km spaced grid covering Switzerland

27 The process of hazard computing Map of epicenters and source zones used Cumulative frequency-magnitude distribution of events

28 The process of hazard computing Logic tree : epistemic vs. aleatory

29 Variability and Uncertainty Aleatory Variability Natural randomness in a process Accommodated in the hazard integral Affects the shape of the hazard curve Epistemic Uncertainty Scientific uncertainty in our models of the process Incorporated through logic trees Leads to alternative hazard curves (fractiles)

30 Seismic Hazard of Switzerland 5% damped horizontal acceleration response spectrum, 5Hz, 475 yr

31 Seismic hazard of Switzerland SA cm/s 2

32 Hazard de-aggregation, Basel

33 Conclusions PSHA is improving rapidly, and requires todays multidisciplinary competences, multiple expert elicitation, cross-border cooperation Regional PSHA is not yet stable Local hazard and simulation hazard are coming, and will soon replace regional PSHA in several regions i.e. Alpine valleys, selected cities We need to focus on: near-fault shaking de-aggregating uncertainties calibrating for local conditions We cannot continue to work at national level only, it is time to have in Europe a reference hazard model(s)