Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

318 1 2 T H I N T E R N AT I O N A L I N Q U A M E E T I N G O N PA L E O S E I S M O L O G Y , A C T I V E T E C T O N I C S A N D A R C H A E O S E I S M O L O G Y ( PATA ) , O C T O B E R 6 T H - 1 1 T H , 2 0 2 4 , L O S A N D E S , C H I L E PATA Days 2024 K E Y W O R D S surface rupture, distributed faulting, PFDHA, numerical modeling (1) GEO-HAZ ConsultingInc., Crestone, Colorado, USA *Email: mccalpin@geohaz.com James P. McCalpin (1) PREDICTING DISTRIBUTED FAULT DISPLACEMENTS AT FORSMARK NUCLEAR WASTE REPOSITORY, SWEDEN: ROCK MECHANICS APPROACH VS GEOLOGIC-EMPIRICAL APPROACH A B S T R A C T TheplannedForsmarkRepository lies 120kmnorthof Stockholm in the Fennoscandian Shield (a Stable Continental Region). Surface faulting occurred during and after the MIS2 deglaciation, and is thus a concern for design over the ~100 kyr planning period, which covers the next glacial-deglacial cycle. Several bedrock faults near the Repository were identified as susceptible to reverse-fault reactivation during the next deglacial cycle. Earthquake- induced slip on fractures & faults within the Repository was then calculated by consultants using the rock mechanics software 3DEC. 3DEC scenario displacements on fractures are invariably smaller than distributed fault displacements observed in historic surface ruptures, for the same earthquake magnitudes and distances. Fracture displacements predicted from Particle-flow code (PFC 3D v4) software are closer to observed slips, and PFC slips on deformation/ shear zones are closer still. This implies that most distributed faulting observed in historic surface ruptures represents reactivations of shear zones, not simple fractures. I N T R O D U C T I O N The method of Probabilistic Fault Displacement Hazard Analysis (PFDHA) was formulated in the late 1990s for the proposed Yucca Mountain Nuclear Waste Repository in Nevada, USA (Youngs et al., 2003). It predicted two parameters: (1) probability of, and surface displacement on, the main seismogenic fault trace (Principal fault, PF), and (2) the same parameters on