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Abstract: We present field data from segmented normal faults having particular displacement and overlapping geometries that may be related to down-dip branching of the fault segments. Based on a 3-D numerical modeling study of computed displacement and stress fields around different geometries of down-dip branched normal fault segments, we show that the bends of fault surfaces that coalesce at depth exert a significant influence on (1) the displacement distribution on the fault segment branches and (2) the quasi-static stress fields around the relay zones. The asymmetry in the displacement profiles and low fault interaction at relay zones modeled are consistent with the fault segment geometries observed in field data. As an application, we model the geometry and interaction of the Vallo di Diano normal fault which is segmented at the Earth''s surface and which produced an earthquake of magnitude 6.4 along a single fault surface at depth. Numerical modeling of the segmented fault produces an asymmetric displacement profile and low shear stress at the relay zone consistent with the profile and fault interaction inferred from the field. We conclude that asymmetry of the displacement profile and large overlap/separation ratio of the unlinked relay zone can be indicators of the presence of a continuous fault surface underneath. These geometrical attributes are therefore important to consider in the probabilistic analysis of seismic hazard along segmented normal faults. [Copyright &y& Elsevier]

Deformation bands in porous volcaniclastics are little studied structural heterogeneities despite their relevance for constraining the modalities of deformation development and related fluid-rock interactions in volcanic areas. We document a dense network of normal-sense Deformation Bands (Normal-sense Compactional Shear Bands (NCSBs) affecting upper Pliocene felsic glassy tuffites in Milos, Greece. NCSBs probably formed between 300 and 500 m of burial depth, in response to NE-SW directed extension which is related to volcanic rift development in the area. They accommodate mm-to m-shear-offsets, trend either N105 ± 10° or N070 ± 10°, and show mutual cross-cutting relations. The NCSB fault rock is made of ultracataclasite in which the cataclastic mechanisms have affected both the mineral fraction and the volcanic glass. Minerals are fractured along their cleavages whereas pumices are interestingly fractured along their vesicles. The development of chemical alteration (dissolution and cementation) essentially into the ultracataclasite is expressed through glass-hosted corrosion gulfs and smectites filling the intergranular porosity. These observations support that NCSBs preferentially retained water, have been the seat of greater fluid flow, and are the locus of ongoing phyllosilicate self-sealing in the vadose zone. A significant decrease (up to one order of magnitude) in porosity is measured within the studied NCSBs. • We document Normal-sense Compactional Shear Bands (NCSBs) in porous volcaniclastics. • Pumice vesicles are zones of mechanical weakness promoting cataclasis development. • Glass alteration is expressed by corrosion embayments and smectites neoformation. • This study details hydraulic self-sealing of NCSBs in the vadose zone. [ABSTRACT FROM AUTHOR]