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A Comparative Study of Earthquake Ground-Shaking Site Effects From Lacustrine Sediments in a Subduction Zone Setting Using Active and Passive Seismic Methods

Description: 

Lacustrine paleoseismology has evolved into a primary technique to reconstruct the recurrence of ground motion at a given site. Different types of sedimentary shaking imprints (e.g., turbidites, landslides) have been linked to various seismic ground motion parameters (e.g., intensity, duration, frequency content). Understanding the depositional characteristics of such imprints thus has great potential to improve local seismic hazard estimations. By defining ground-motion threshold values for the appearance and absence of certain coseismic imprints, earthquake magnitude and source location can be estimated via ground-motion modelling. However, up to now the input for these models has remained limited to rather qualitative measures of strong ground motion that are poorly physically constrained (i.e., macroseismic intensity). This is partly related to the gap in our understanding of the site characteristics of lake sediments, as direct observations of seismic shaking on the bottom of a lake are scarce.

To get a first idea on the variability of ground-shaking site effects in lakes and how these relate to the depositional environment, we study two sites in southern Chile and south-central Alaska located at ~200 km from the subduction trench by analyzing ambient noise geophone array registrations as well as hammer seismic data. The Alaskan site consists of a 4.4 km² drained proglacial lake in mountainous terrane (Iceberg Lake) containing ~1500 years of outcropping sediments in an actively eroding environment. In Chile, measurements were performed along the shores of the 860 km² piedmont Lago Llanquihue, where lake sediments with an (up to now) unclear age are buried at shallow depth. Preliminary analysis shows that Vs30 values are very similar, while H/V spectral ratios and fundamental frequencies are more variable within and between sites, emphasizing the need for detailed site studies in any lacustrine paleoseismic study. Ongoing analysis will focus on understanding the origin of these differences, and how this knowledge can contribute to the interpretation of other lacustrine paleoseismic records.

Session: From Faults to Fjords: Earthquake Evidence in Terrestrial and Subaqueous Environments [Poster Session]

Type: Poster

Date: 5/1/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Katleen

Student Presenter: No

Invited Presentation: 

Authors