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High-Resolution Fault Imaging From Fault Zone Guided Waves Recorded by Dense Arrays in the Aftershock Zone of the 2023 Kahramanmaras Earthquake Sequence in Southern Türkiye

Description: 

The 2023 Kahramanmaras earthquake sequence includes a M 7.8 earthquake initiated near Nurdağı in Gaziantep ruptured for more than 300 km along the East Anatolian Fault (EAF) in Southern Türkiye, and a M7.5 event near Ekinözü in Kahramanmaraş Province nine hours later. These events were followed by numerous aftershocks around both mainshock rupture zones. To better capture the ongoing aftershock sequence, we deployed up to 200 5-Hz Smartsolo nodal stations and 16 broadband/strong motion stations across nearly the entire rupture zone for more than three months. Our array also includes a one-month deployment of an ultra-dense fault zone profile across the Pazarcık segment of the EAF and the Sakçagöz-Narlı Fault (SNF) where the M7.8 mainshock initiated. In this study, we present clear evidence of seismic waves generated by fault zone structures and use them for high-resolution imaging of the low-velocity damage zone (LVDZ) across the EAF. We first select ~80 events within 20 km of the array center (C000), which is situated at the surface rupture of the M7.8 mainshock. We then rotate the two horizontal components to fault-parallel and fault-normal directions, and visually identify fault zone trapped waves (FZTWs) as long-period dispersive waves due to internal reflections within the LVDZ following the direct S waves at stations immediately surrounding the EAF. We find that FZTWs are recorded at more stations east of the array center rather than to the west, likely indicating an asymmetry in the LVDZ. Alternatively, it is related to the presence of quaternary basin with an estimated thickness of ~250 m based on the HVSR method. Our preliminary analysis shows that aftershocks directly beneath both two parallel faults can generate FZTWs recorded at stations along the Pazarcık segment of the EAF. Our next step is to quantify the degrees of FZTWs for events at different locations, and combine both FZTWs and time delays of direct P and S waves to better constrain the depth extent and geometry of the damage zone associated with the M7.8 mainshock.

Session: Illuminating Complex, Multiplet Earthquake Sequences at Kahramanmaras (Turkiye), Herat (Afghanistan), and Beyond - II

Type: Oral

Date: 5/2/2024

Presentation Time: 10:30 AM (local time)

Presenting Author: Zhigang

Student Presenter: No

Invited Presentation: 

Authors