Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

440 1 2 T H I N T E R N AT I O N A L I N Q U A M E E T I N G O N PA L E O S E I S M O L O G Y , A C T I V E T E C T O N I C S A N D A R C H A E O S E I S M O L O G Y ( PATA ) , O C T O B E R 6 T H - 1 1 T H , 2 0 2 4 , L O S A N D E S , C H I L E PATA Days 2024 (1) Department of Earth and Environmental Sciences, San Diego State University, San Diego, CA 92182. . (2) Department of Earth Science, University of California Santa Barbara, Santa Barbara, CA 93106 *Email: trockwell@sdsu.edu K E Y W O R D S Subduction zone models, Mariana trench, Guam earthquake potential. Thomas Rockwell (1) Rafael Almeida (1) Alexander R. Simms (2) CAN THE MARIANA SUBDUCTION COMPLEX GENERATE M9 CLASS MEGATHRUST EVENTS? TESTING THE CLASSIC UYEDA AND KANAMORI SUBDUCTION ZONE MODEL IN GUAM A B S T R A C T Traditional models of subduction zones consider the Marianas Trench (MT) as aseismic (Uyeda and Kanamori, 1979). However, Muhs et al. (2020) demonstrated that Saipan is rising at ~0.2 mm/ yr, similar to the rate along the Chilean margin. We collected preliminary data from Guam that demonstrates both relatively rapid long-term uplift and evidence of Holocene uplift in the form of raised sea-level notches. The four main islands of the Marianas (Guam, Rota, Tinian, Saipan) that represent the former volcanic arc are 50-60 km east of the current arc implying a decrease in dip of the subduction interface from an average of about 31 o to 25 o , which is similar to much of the arc to the north, as well as other subduction zones that have generated M9 earthquakes. These observations argue that the Uyeda and Kanamori model is likely wrong and that the MT may experience megathrust events in the future. I N T R O D U C T I O N The classic model by Uyeda and Kanamori (1979) classifies subduction zones into their seismic potential, based in part on the rate of uplift of the hanging wall and the dip of the subduction interface. They model two end members, the Mariana and Chilean subduction zones, with the Mariana subduction zone being aseismic and the Chilean subduction zone being fully coupled. This contrast implies a difference in rate of forearc uplift between these end-members as well. However, Muhs et al. (2020) demonstrated that Saipan, one of the four main islands of the extinct Mariana island arc chain above the Mariana subduction zone, is rising at up to 0.19 mm/yr, similar to the uplift rate along the Chilean margin.