Conference Agenda

The ability of luminescence dating to constrain the timing of past earthquakes depends on adequate thermal elevation during frictional heating of fault gouges. Laboratory friction experiments can approximate a range of slip conditions by varying normal stress and slip velocity, and they record the resulting temperatures with thermocouples or infrared cameras. However, replicating such measurements in natural is impractical. Systematic studies of ultraviolet (UV) radiofluorescence (RF) in quartz have shown a strong correlation between the degree of heating and the subsequent UV‑RF signal evolution.

Our investigation evaluates the capability of ultraviolet radio‑fluorescence (UV‑RF) to quantify friction‑induced temperature rise in quartz‑bearing host rocks. Experiments were carried out on two types of materials: a sedimentary quartz specimen with a well‑characterized luminescence signature, and a polymineralic rock sourced from the North Tehran Fault. For each material, one half of the sample was subjected to controlled heating in temperature, and the resulting UV‑RF temperature profiles were recorded. The remaining, untreated half was then sheared using a rotary shear apparatus with a normal stress of 12 MPa and a slip velocity of 5 cm s⁻¹. The friction-induced temperature was estimated using UV‑RF signal by projecting onto a signal pre-heat profile.

The results indicate that realistic friction‑induced temperatures can reliably be calculated for the quartz sample. In contrast, the UV‑RF responses of the polymineralic sample remain inconclusive, necessitating additional experimentation. We will discuss the potential of this method for tracking earthquake‑generated temperature regimes.

Offshore faults pose a significant seismic hazard to coastal regions, yet assessing them is challenging because of their subamarine location. Erosive marine terraces form at sea level through wave erosion and are later uplifted by tectonic processes, making them geomorphic records of long-term vertical movement. Thereby, they offer an indirect way to study offshore fault activity.

The Japanese island Sado features several offshore faults nearby the coast, as well as a well-developed marine terrace sequence. Sado’s marine terraces have been geomorphologically mapped and correlated to marine isotope stages (MIS), however, no numerical ages exist yet, leaving the island’s uplift history unclear.

The nearby Noto Peninsula, which is characterised by a comparable tectonic and geomorphological environment, has been successfully dated using optically stimulated luminescence (OSL) of beach sand covering marine terraces that correlate with marine isotope stage 5 within a broader marine terrace sequence. On Sado, however, the terrace deposits consist mainly of coarse clasts of volcanic rocks, and suitable sand for OSL dating is largely absent. To overcome this limitation, we tested rock surface luminescence dating of cobbles and pebbles collected from terraces correlated with MIS 5e, with the aim of establishing the first numerical chronology for Sado’s marine terrace sequence.

Most of the cobbles examined yielded saturated luminescence signals, suggesting their exposure age exceeds their dating range. Despite these limitations, we report ages from a limited number of sand-sized terrace sediments and cobbles, which provide depositional age constraints and allow preliminary estimates of co-seismic uplift rates for Sado Island.

The Eastern Alps are a slowly deforming region characterized by infrequent earthquakes. The Pleistocene glaciations extensively removed geomorphic markers, and both short-term instrumental methods and traditional paleoseismology are difficult to apply. Consequently, it remains unknown when major faults such as the eastern Periadriatic Fault (PAF) were last active. To evaluate Quaternary seismic activity, we applied electron spin resonance (ESR, quartz) and optically stimulated luminescence (OSL, K-feldspar) dating to fault gouges from the PAF and kinematically linked neighboring faults. These methods are sensitive to temperatures >100°C and record signal resetting by shear heating during surface-rupturing earthquakes.

Our findings revealed varying levels of activity, using signal saturation as a comparative metric. The Lavanttal Fault revealed complete ESR signal saturation (>86%), suggesting limited activity related to surface-rupturing earthquakes since ~2 Ma. The PAF yielded ESR ages from ~1 Ma to 300 ka, and minimum OSL ages from ~280 to 62 ka. An average ESR saturation of 66% indicated consistent seismic activity along this fault. For the Šoštanj Fault, ESR and OSL remained below saturation (49% and 14%, respectively), yielding respective ages of ~650 ka and 30 ka, which suggested a more recent activity.

These findings confirm that the PAF remained seismically active in the Quaternary, while numerical models in ESR thermochronometry indicated a long earthquake recurrence interval in the 100 ka to 1 Ma scale. More broadly, our work demonstrates how these methods can successfully bridge the gap between short-term instrumental data and long-term geological records, helping to improve regional seismic hazard assessments.

Earthquakes in slowly deforming areas are quite an enigma in active tectonics. One aspect hindering our understanding of these events is their long recurrence time and hence often limited surface expression making it particular challenging to identify the causative faults with classic geomorphic methods. However, these earthquakes can pose a substantial threat to society as they often occur in poorly prepared areas with insufficient seismic hazard awareness. Therefore, it is essential to improve our knowledge about these areas despite their limited suitability for traditional research approaches.

One example of an enigmatic, slowly deforming area is the westernmost Tuscan Northern Apennines (Italy). An area generally assumed to be of low to moderate earthquake hazard but still severely shaken by the ~M6 Orciano Pisano earthquake in 1846. The exact source location of this event remains undefined, but it is thought to be in the Val di Fine Basin near the Tyrrhenian coast (CPTI15; Piccardi et al., 2017).

To verify this assumption and identify the causative fault we carried out an extensive tectono-geomorphic analysis combining a remote sensing approach with field work and a detailed analysis of the seismological record. However, only after the reconstruction of the complex long-term development of the basin the assembled data began to create a coherent picture. The results of our analysis points towards the possible existence of a previously unrecognised transversal structure within the frame of the dominating N-S trending fault system. This secondary fault crossing the basin could be the source of the 1846 event.

The Motagua Fault in Guatemala is part of the plate boundary between the North American and Caribbean plates. It ruptured in a M7.5 earthquake in 1976 with a 230 km-long surface rupture and an average slip of about 1 m. The tectonic geomorphology of this fault is poorly documented and the impact of repeated strong earthquakes on the fault damage zone is not well understood. Using new airborne LiDAR data, near-surface geophysics, paleoseismological trenching, radiocarbon dating, and historical data, we investigated a pull-apart basin at the Estanzuela site. We dug trenches across the northern topographic scarp of the basin and the basin center to locate and investigate the main fault zone. We show that the pull-apart basin today is controlled by a fault bend rather than a step-over. Geophysical data confirm this interpretation. Radiocarbon results from the fault damage zone show that repeated surface-rupturing earthquakes result in open fractures in the center of the fault zone, which are then filled by near-surface sediments. Networks of fractures that accommodate distributed shear could be documented over 80 m around the main fault strand at this site. We show that the off-fault deformation decreases with increasing distance from the main fault zone. These data illustrate the anatomy of the plate boundary. We speculate that off-fault deformation may contribute, albeit only a small portion, to the apparent low fault length-to-offset ratio observed in 1976.