Directivity Effect of the 1976 Guatemala Earthquake Observed in Lacustrine Turbidites
Description:
On 4 February 1976, a Mw 7.5 earthquake along the Motagua Fault in Guatemala ruptured more than 230 km of the North American and Caribbean plate boundary in an event that killed ~23,000 people and left ~ 1.5 million people homeless. Today, the plate boundary remains poorly monitored, with few instrumental and historical records to assess seismic hazard. In this study we present new radiometrically-dated sediment core data to evaluate the recent sedimentary record from four lakes in the vicinity of the plate boundary. Seismic shaking resulted in mass wasting and turbidity currents in all studied lakes, leaving behind a detailed record of sedimentation events triggered by the 1976 earthquake. Comparison between shaking maps and sediment core data reveals a complicated relationship between earthquake parameters and thickness of sediment gravity flow deposits. Our results show that thicker event deposits are present at lakes near the terminus of the Motagua Fault and thinner off-axis of the rupture direction. We hypothesize that this relationship between earthquake rupture direction and earthquake-induced sedimentation event thickness arises from a directivity effect of the earthquake, with more shaking experienced at the site in line with the rupture direction. The lake deposits constrain the asymmetrical distribution of shaking during large earthquakes and will help in the interpretation of long sediment records from this and related strike-slip fault systems. The observed relationship between earthquake directivity and severe seismic shaking can also help in the assessment of seismic hazard along this poorly studied plate boundary.
Session: Earthquake Shaking and the Geologic Record: Triggered Phenomena and Preserved Fragile Geologic Features - I
Type: Oral
Date: 4/17/2025
Presentation Time: 02:30 PM (local time)
Presenting Author: Jeremy
Student Presenter: No
Invited Presentation:
Poster Number:
Authors
Jeremy Maurer Presenting Author Corresponding Author jmaurer@mst.edu Missouri University of Science and Technology |
Jonathan Obrist-Farner obristj@mst.edu Missouri University of Science and Technology |
Derek Gibson derek.gibson@siu.edu Southern Illinois University |
Trenton McEnaney tmfnc@mst.edu Missouri University of Science and Technology |
Andreas Eckert eckertan@mst.edu Missouri University of Science and Technology |
William Kenney kenney@ufl.edu University of Florida |
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Directivity Effect of the 1976 Guatemala Earthquake Observed in Lacustrine Turbidites
Session
Earthquake Shaking and the Geologic Record: Triggered Phenomena and Preserved Fragile Geologic Features