Moment Tensors of Ring‐Faulting at Active Volcanoes: Insights Into Vertical‐CLVD Earthquakes at the Sierra Negra Caldera, Galápagos Islands

Abstract

Dip slip along curved ring faults at volcanoes generates Mw > 5 earthquakes dominated by a compensated-linear-vector-dipole component. We propose a method for estimating ring-fault parameters by moment tensor inversion using long-period seismic data.

Physics‐Based Model Reconciles Caldera Collapse Induced Static and Dynamic Ground Motion: Application to Kīlauea 2018

“…Additional processes during caldera collapse, such as slip on non‐vertical ring faults (Sandanbata et al., 2021), potentially contribute to co‐collapse ground motions and dynamics. Slight changes in ring fault dip have been demonstrated to influence extra‐caldera static deformation (Segall et al., 2019), but its effect on dynamic ground motion, in conjunction with mechanisms in the present study, needs to be further investigated.…”

Sub-decadal Volcanic Tsunamis Due to Submarine Trapdoor Faulting at Sumisu Caldera in the Izu-Bonin Arc

“…Figure 6 compares trapdoor faulting motions, moment tensors, and synthetic seismograms of three models with different dip angles (but similarly with a 2/3-ring arc length), showing that the amplitudes of seismic waveforms are significantly different despite similar slip amounts and Mw determined by the tsunami waveform inversion. This is because the ring-faulting at such a shallow depth becomes less efficient in radiating long-period seismic waves as the dip angle becomes closer to the vertical (Sandanbata, Kanamori, et al, 2021). From the seismic NRMS misfits (Figure 4), we determine optimal dip angles to be 85.0°, 85.5°, and 83.5 for 2/3, full, and 1/3-ring arc lengths, respectively.…”

“…The preference of the 2/3-ring arc-length model over the other two models can be seen in the better phase fits of the horizontal and S12d). As shown in Sandanbata, Kanamori, et al (2021), the seismic radiation pattern of the ring faulting is sensitive to the ring-fault arc length, and the side on which the ring-fault is placed, because of the geometrical cancelation of double-couple components of the moment tensor (see Figure 2 of Sandanbata, Kanamori, et al, 2021, for example). This property causes differences in seismic waveforms of the three arc-length models, which helps us to select the 2/3-ring arc-length model as the most preferable model.…”

“…These highlight the very small long-period seismic excitations from the horizontal crack and the two elements (𝑀 DE and 𝑀 DF ) of the ring fault that occur at shallow depths near the free-traction seafloor surface (pp. 180-183 of Dahlen & Tromp, 1998; manuscript submitted to Journal of Geophysical Research: Solid Earth Fukao et al, 2018;Sandanbata, Kanamori, et al, 2021). Thus, despite the seismic magnitude Mw 6.16 of 𝑴 𝑯𝑪 + 𝑴 𝑹𝑭 (a seismic moment M0 = 2.16 ´ 10 18 Nm; Figure 7a), only the limited part of the ring faulting 𝑴 𝑹𝑭 , excluding the two elements, that corresponds to Mw 5.71 (M0 = 0.46 ´ 10 18 Nm; equivalent to 22% of the total seismic moment; Figure 9c), contributes the long-period seismic radiation of the trapdoor faulting.…”

“…Based on the geodetic observations, previous studies (e.g., Amelung et al, 2000;Yun, 2007;Zheng et al, 2022) showed that the ring-faulting that interacts with the deformation of its underlying sill-like magma reservoir can cause an asymmetric caldera deformation; this mechanism is referred to as trapdoor faulting. The seismic radiations from the trapdoor faulting events were characterized by vertical CLVD moment tensors (Sandanbata, Kanamori, et al, 2021;. Similarly, the trapdoor faulting mechanism is presumed to have generated large asymmetric coseismic uplift of Sumisu caldera (as shown in…”