EARTHQUAKE HAZARD ASSESSMENT IN KAZAKHSTAN Dr Ilaria Mosca 1 and Dr Natalya Silacheva 2 1 British Geological Survey, Edinburgh (UK) imosca@nerc.ac.uk 2 Institute of Seismology, Almaty (Kazakhstan) silacheva_nat@mail.ru Almaty, Kazakhstan 7 September 2016
Overview Seismic hazard assessment Deterministic approach Probabilistic approach
Seismic hazard assessment Earthquake hazard: The potential for dangerous earthquakerelated phenomena, including ground shaking, soil liquefaction and fault ruptures at the ground surface. The hazard depends on many parameters: Size and location of future earthquakes; How often they occur; The geological conditions that affect how the seismic waves propagate. Seismic hazard assessment is the calculation of the seismic hazard for a site or for a wider area and accounts for information from geology, seismology and geophysics.
Approaches for seismic hazard assessment Deterministic seismic hazard assessment (DSHA). DSHA considers a single earthquake scenario, usually the largest in the study area, to estimate the ground shaking at the site under investigation.
Approaches for seismic hazard assessment Deterministic seismic hazard assessment (DSHA). DSHA considers a single earthquake scenario, usually the largest in the study area, to estimate the ground shaking at the site under investigation. Probabilistic seismic hazard assessment (PSHA). PSHA identifies all possible earthquake scenarios in the study area, including all possible combinations of magnitude and source-to-site distances.
Uses of DSHA When to use DSHA? To inform disaster risk reduction policy Community-based risk reduction activities To consider the worst case scenario Earthquake preparedness activity in Dhaka, Bangladesh
Uses of PSHA When to use PSHA? Engineering projects Insurance and reinsurance purposes From https://en.wikipedia.org/wiki/bellefonte_nuclear_generating _Station From https://en.wikipedia.org/wiki/list_of_dams_and_reservoirs
Topography in Central Asia
Seismicity in the Northern Tien Shan TFF=Talas-Ferghana fault CKCF=Chon-Kemin-Chilik fault Tectonic structures from http://activetectonics.la.asu.edu/n_tien_shan/n_tien_shan.html
Building a deterministic scenario STEP 1: Defining earthquake sources 3 January 1911 Chon- Kemin earthquake Epicentre: 42.80 E and 77.30 W Moment magnitude Mw of 8.02 (Kulikova & Krüger, 2015) Total rupture of 145-200 km on six different segments (e.g. Molnar & Ghose, 2000; Kulikova & Krüger, 2015)
Building a deterministic scenario STEP 2: Selection of the controlling earthquake Moment magnitude Mw of 8.02 Total rupture of 202 km Reverse focal mechanism with a strike-slip component Almaty (64 km from the epicentre) (not to scale)
Building a deterministic scenario STEP 3: Selection of the ground motion model Ground motion models describe the ground shaking produced by an earthquake for a given set of parameters, such as magnitude, source-to-site distance, style of the faulting, geological conditions, etc.
Building a deterministic scenario STEP 4: Hazard calculations Simulation of peak ground acceleration (PGA) for the 1911 Chon- Kemin earthquake for rock conditions. PGA: the maximum ground acceleration produced by an earthquake at a particular location. PGA=0.60 0.18 g at the epicentre PGA=0.278 0.082 g in Almaty
Building a deterministic scenario STEP 4: Hazard calculations Simulation of intensity for the 1911 Chon-Kemin earthquake for rock conditions. Intensity describes the severity of ground shaking from an earthquake on the basis of the effects on objects, people and buildings. Intensity= 9-10 at the epicentre Intensity= 8-9 in Almaty Intensity (MSK-64)
Summary We simulated the ground shaking at a site in Almaty for the largest historical earthquakes in the Northern Tien Shan region. 1911 Mw 8.0 1889 Mw 8.2 1887 Mw 7.4 Chon-Kemin Chilik Verny PGA [g] 0.278 ± 0.082 0.231 0.069 0.57 0.17 Intensity 8-9 8-9 8-9
Summary We simulated the ground shaking at a site in Almaty for the largest historical earthquakes in the Northern Tien Shan region. 1911 Mw 8.0 1889 Mw 8.2 1887 Mw 7.4 Chon-Kemin Chilik Verny PGA [g] 0.278 ± 0.082 0.231 0.069 0.57 0.17 Intensity 8-9 8-9 8-9 Clear and intuitive to engineers and other stakeholders (e.g. local administrators).
Summary We simulated the ground shaking at a site in Almaty for the largest historical earthquakes in the Northern Tien Shan region. 1911 Mw 8.0 1889 Mw 8.2 1887 Mw 7.4 Chon-Kemin Chilik Verny PGA [g] 0.278 ± 0.082 0.231 0.069 0.57 0.17 Intensity 8-9 8-9 8-9 Clear and intuitive to engineers and other stakeholders (e.g. local administrators). The disadvantage of DSHA: the results are not associated with a probability of occurrence. This problem can be solved using PSHA.
PSHA Probabilistic Seismic Hazard Assessment Combining information from seismology, tectonics, geology, and kinematics, PSHA considers all future possible earthquake magnitudes at all possible distances in the study area with an allowance for recurrence frequency. PSHA may include alternative models of earthquake sources, recurrence periods, predictive relationships as well as uncertainties stipulated both by indistinct knowledge of parameters (epistemic) and random nature of seismic events (aleatory). Aleatory uncertainties - Future earthquake locations - Future earthquake source properties (e.g. M) - Ground motion at site - Details of fault rapture process Epistemic uncertainties - Geometry of seismotectonic and seismogenic zones - Distributions describing source parameters (a, b, Mmax) - Median value of ground motions - Limits on ground shaking PSHA compute the ground shaking at a site (or at a grid of sites) within a time window, for example 50 years (service life of standard buildings). PSHA output is a hazard curve, demonstrating the probability of exceeding a certain amount of ground shaking at a site within a time window. PSHA is preferred in engineering and reinsurance. PSHA maps are also helpful in seismic risk mitigation and management.
PSHA procedure in four steps: 1- Identification and characterization of potential earthquake sources, which are areas close to the site where the probability of the occurrence of the earthquakes is equal in each source. A set of seismic sources is called seismic source model. 2 - Computation of the annual number of earthquakes in each seismic source using the catalogue of earthquakes that have occurred in the source model. 3 - Computation of the ground shaking produced at the site by earthquakes of all possible sizes in the seismic sources. 4 - Estimation of the probability that the ground motion will be exceeded during a particular time period. From Reiter (1990)
Seismic Hazard in Kazakhstan Until now the Kazakhstan s Building code (BC) for seismic design is based on the deterministic approach. Methodology, mapped parameters and the presentation of result considerably differed from the western approach. Kazakhstan s seismologists already use the PSHA procedure which meets the requirements of Eurocode 8 (European standard regulating building in earthquakeprone regions). Institute of Seismology together with other Kazakhstan Institutions (Kazakhstan National Data Centre, Kazakhstan Geotechnical Institute for Survey, Kazakhstan Scientific-Research and Design Institute of Construction and Architecture), and the support of the seismology group of the British Geological Survey develop the Probabilistic General Seismic Zoning maps (GSZ) of Kazakhstan using domestic experience and foreign achievements. The new GSZ maps will be the basis for updating Kazakhstan s BC for seismic design. Methodology used for probabilistic GSZ of Kazakhstan
Probabilistic General Seismic Zoning (GSZ) of Kazakhstan The main differences from the previous GSZ : 1)PSHA instead of DSHA 2)Hazard estimates expressed in terms of both intensity (MSK-64(K)) and peak ground acceleration Updated databases (catalogs, maps of zones of probable earthquake sources, predictive models), Modern software Logic tree for analysis in PGA : 1) 94 seismic sources 2) 3 seismotectonic regimes: active (AR), stable (SR), subduction (SZ) 3) attenuation models: 4 for AR - AkBo10, ChYo08, BoAt08, CaBo08 4 for SR - PeEA2011, AtBo2006, SiEA02, ToEA97 2 for SZ - AtBo03, ZhEA06. 4) two recurrence periods 475 and 2500 years an example for one branch of LT
General Seismic Zoning maps of the territory of Kazakhstan using PSHA in terms of PGA The hazard values are contoured to give a picture of the spatial variation of the hazard. The largest hazard corresponds to the Southern, Southeastern and Eastern Kazakhstan territory; and the remaining country has low to moderate levels of hazard. for a return period of 475 years Uniform Hazard Spectra and Hazard Curve for CSO site in Almaty for a return period of 2475 years
General Seismic Zoning maps of the territory of Kazakhstan using PSHA in terms of macroseismic intensity scale MSK-64(K) List of settlements in the Republic of Kazakhstan located in earthquake prone regions with their intensity and PGA values for a return period of 475 years for a return period of 2475 years
The set of GSZ maps is presented to engineers for recommendations on their corrections and preparing for further usage in normative documents. The map of seismic microzoning for Almaty city is now under development and background seismic hazard for it is also based on the PSHA methodology. Thus: -The probabilistic approach includes the deterministic as a subset and includes consideration of uncertainties. -The SHA methodology, mapping parameters and representation of results in Kazakhstan considerably differed from the western approach. - The new probabilistic GSZ map will meet the scientific and methodical requirements of Eurocode 8.