WeAreSeismicaJun 19, 2024

How can we image the dip of distributed fault zones with seismicity?

Read how Ross extracts the fault zone geometry: https://doi.org/10.26443/seismica.v3i1.1092

#faultstructure #hypocenter #Seismology #EarthquakeScience #peerreviewed #DiamondOpenAccess #Earthquake #OpenAccess #OpenScience

Insights on the dip of fault zones in Southern California from modeling of seismicity with anisotropic point processes

Accurate models of fault zone geometry are important for scientific and hazard applications. While seismicity can provide high-resolution point measurements of fault geometry, extrapolating these measurements to volumes may involve making strong assumptions. This is particularly problematic in distributed fault zones, which are commonly observed in immature faulting regions. In this study, we focus on characterizing the dip of fault zones in Southern California with the goal of improving fault models. We introduce a novel technique from spatial point process theory to quantify the orientation of persistent surficial features in seismicity, even when embedded in wide shear zones. The technique makes relatively mild assumptions about fault geometry and is formulated with the goal of determining the dip of a fault zone at depth. The method is applied to 11 prominent seismicity regions in Southern California. Overall, the results compare favorably with the geometry models provided by the SCEC Community Fault Model and other focused regional studies. More specifically, we find evidence that the Southern San Andreas and San Jacinto fault zones are both northeast dipping at seismogenic depths at the length scales of 1.0–4.0 km. In addition, we find more limited evidence for some depth dependent variations in dip that suggest a listric geometry. The developed technique can provide an independent source of information from seismicity to augment existing fault geometry models.

Seismica
WeAreSeismicaJul 8, 2023

Evangelidis et al. image the western edge of the Aegean Shear Zone using the South Evia 2022-2023 Seismic Sequence.

They identify the activation of a NW-SE fault structure, emphasizing the urgency for better seismic network coverage in the region.

Read: https://seismica.library.mcgill.ca/article/view/1032

#seismology #earthquake #Aegean #faultstructure #strikeslip #seismicnetwork #machinelearning #seismichazard

Imaging the Western Edge of the Aegean Shear Zone: The South Evia 2022-2023 Seismic Sequence

This report presents the 2022-2023 South Evia island seismic sequence, in the western Aegean sea. An automated workflow, undergoing testing for efficient observatory monitoring in the wake of dense aftershock sequences, was employed to enhance the seismic catalog. It includes a deep-learning phase picker, absolute and relative hypocenter relocation, and moment tensor automatic calculations. The relocated catalog reveals a concentration of earthquake epicenters in a narrow NW-SE zone, with sinistral strike-slip fault movement. The findings of the study indicate the occurrence of an asymmetric rupture within conjugate fault structures in the western Aegean region. These fault structures, although not necessarily both active, play a significant role in marking the transition from dextral (SW-NE) to sinistral (NW-SE) strike-slip ruptures, connecting the Aegean shear zone with normal faulting in mainland Greece. The South Evia 2022-2023 seismic sequence has revealed the activation of this NW-SE strike-slip structure, contrary to previous assumptions of low seismicity in the region. The study highlights the importance of reassessing seismic hazard maps and considering the potential activation of similar zones further south in the future. It also emphasizes the need for the expansion and the densification of seismic networks within the Aegean.

Seismica