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Chen W, Wei S, Wang W. Subslab ultra low velocity anomaly uncovered by and facilitating the largest deep earthquake. Nat Commun 2024; 15:2754. [PMID: 38553481 PMCID: PMC10980710 DOI: 10.1038/s41467-024-47129-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2023] [Accepted: 03/21/2024] [Indexed: 04/02/2024] Open
Abstract
It is enigmatic that M8+ earthquakes can take place at depth greater than 600 km inside the slab, where the P-T conditions generally do not favor seismic slip rate (~m/s) on faults. Here we provide fresh insights to the initial rupture and mechanism of the Mw 8.3 Sea of Okhotsk earthquake by analyzing high-frequency (up to 0.8 Hz) teleseismic array data. We determine the relative location and timing of two early subevents, and the geometry and velocity perturbation of a nearby structure anomaly. We found a small-scale (~30 × 60 × 60 km) ultralow (-18 ± 2%) P-wave velocity anomaly located beneath the Pacific slab around the 660 km discontinuity. The volatile-bearing highly melted nature of the anomaly provides significant buoyancy, stressing the slab dramatically closer to the critical condition for thermal runaway weakening that allows the rupture to propagate beyond the metastable olivine wedge, forming M8+ events. Enormous velocity reduction urges for further mineral physics and geodynamic investigations.
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Affiliation(s)
- Weiwen Chen
- Earth Observatory of Singapore, Nanyang Technological University, Singapore, Singapore
- Institute of Geophysics, China Earthquake Administration, Beijing, China
| | - Shengji Wei
- Earth Observatory of Singapore, Nanyang Technological University, Singapore, Singapore.
- Asian School of the Environment, Nanyang Technological University, Singapore, Singapore.
- Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China.
| | - Weitao Wang
- Institute of Geophysics, China Earthquake Administration, Beijing, China.
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Pino NA, Convertito V, Godano C, Piromallo C. Subduction age and stress state control on seismicity in the NW Pacific subducting plate. Sci Rep 2022; 12:12440. [PMID: 35858891 PMCID: PMC9300704 DOI: 10.1038/s41598-022-16076-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2022] [Accepted: 07/04/2022] [Indexed: 11/09/2022] Open
Abstract
Intermediate depth (70-300 km) and deep (> 300 km) earthquakes have always been puzzling Earth scientists: their occurrence is a paradox, since the ductile behavior of rocks and the high confining pressure with increasing depths would theoretically preclude brittle failure and frictional sliding. The mechanisms proposed to explain deep earthquakes, mainly depending on the subducting plate age and stress state, are generally expressed by single parameters, unsuitable to comprehensively account for differences among distinct subduction zones or within the same slab. We analyze the Kurile and Izu-Bonin intraslab seismicity and detail the Gutenberg-Richter b-value along the subducted planes, interpreting its variation in terms of stress state, analogously to what usually done for shallow earthquakes. We demonstrate that, despite the slabs different properties (e.g., lithospheric age, stress state, dehydration rate), in both cases deep earthquakes are restricted to depths characterized by equal age from subduction initiation and are driven by stress regimes affected by the persistence of the metastable olivine wedge.
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Affiliation(s)
- Nicola Alessandro Pino
- Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Vesuviano, Via Diocleziano, 328, 80134, Napoli, Italy.
| | - Vincenzo Convertito
- Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Vesuviano, Via Diocleziano, 328, 80134, Napoli, Italy
| | - Cataldo Godano
- Dipartimento di Matematica e Fisica, Università della Campania "Luigi Vanvitelli", Via Vivaldi, 43, 81100, Caserta, Italy
| | - Claudia Piromallo
- Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Roma 1, Via di Vigna Murata, 605, 00143, Rome, Italy.
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Zhan Z, Cantono M, Kamalov V, Mecozzi A, Müller R, Yin S, Castellanos JC. Optical polarization-based seismic and water wave sensing on transoceanic cables. Science 2021; 371:931-936. [PMID: 33632843 DOI: 10.1126/science.abe6648] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2020] [Accepted: 01/11/2021] [Indexed: 11/02/2022]
Abstract
Seafloor geophysical instrumentation is challenging to deploy and maintain but critical for studying submarine earthquakes and Earth's interior. Emerging fiber-optic sensing technologies that can leverage submarine telecommunication cables present an opportunity to fill the data gap. We successfully sensed seismic and water waves over a 10,000-kilometer-long submarine cable connecting Los Angeles, California, and Valparaiso, Chile, by monitoring the polarization of regular optical telecommunication channels. We detected multiple moderate-to-large earthquakes along the cable in the 10-millihertz to 5-hertz band. We also recorded pressure signals from ocean swells in the primary microseism band, implying the potential for tsunami sensing. Our method, because it does not require specialized equipment, laser sources, or dedicated fibers, is highly scalable for converting global submarine cables into continuous real-time earthquake and tsunami observatories.
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Affiliation(s)
- Zhongwen Zhan
- Seismological Laboratory, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA.
| | | | | | - Antonio Mecozzi
- Department of Physical and Chemical Sciences, University of L'Aquila, Coppito, Italy
| | | | | | - Jorge C Castellanos
- Seismological Laboratory, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
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Billen MI. Deep slab seismicity limited by rate of deformation in the transition zone. SCIENCE ADVANCES 2020; 6:eaaz7692. [PMID: 32766442 PMCID: PMC7385466 DOI: 10.1126/sciadv.aaz7692] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/23/2019] [Accepted: 03/18/2020] [Indexed: 06/11/2023]
Abstract
Deep earthquakes within subducting tectonic plates (slabs) are enigmatic because they appear similar to shallow earthquakes but must occur by a different mechanism. Previous attempts to explain the depth distribution of deep earthquakes in terms of the temperature at which possible triggering mechanisms are viable, fail to explain the spatial variability in seismicity. In addition to thermal constraints, proposed failure mechanisms for deep earthquakes all require that sufficient strain accumulates in the slab at a relatively high stress. Here, I show that simulations of subduction with nonlinear rheology and compositionally dependent phase transitions exhibit strongly variable strain rates in space and time, which is similar to observed seismicity. Therefore, in addition to temperature, variations in strain rate may explain why there are large gaps in deep seismicity (low strain rate), and variable peaks in seismicity (bending regions), and, possibly, why there is an abrupt cessation of seismicity below 660 km.
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Fichtner A, Simutė S. Hamiltonian Monte Carlo Inversion of Seismic Sources in Complex Media. JOURNAL OF GEOPHYSICAL RESEARCH. SOLID EARTH 2018; 123:2984-2999. [PMID: 30034980 PMCID: PMC6049980 DOI: 10.1002/2017jb015249] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/17/2017] [Revised: 03/05/2018] [Accepted: 03/13/2018] [Indexed: 06/08/2023]
Abstract
We present a probabilistic seismic point source inversion, taking into account 3-D heterogeneous Earth structure. Our method rests on (1) reciprocity and numerical wavefield simulations in complex media and (2) Hamiltonian Monte Carlo sampling that requires only a small amount of test models to provide reliable uncertainty information on the timing, location, and mechanism of the source. Using spectral element simulations of 3-D, viscoelastic, anisotropic wave propagation, we precompute receiver side strain tensors in time and space. This enables the fast computation of synthetic seismograms for any hypothetical source within the volume of interest, and thus a Bayesian solution of the inverse problem. To improve efficiency, we developed a variant of Hamiltonian Monte Carlo sampling. Taking advantage of easily computable derivatives, numerical examples indicate that Hamiltonian Monte Carlo can converge to the posterior probability density with orders of magnitude less samples than the derivative-free Metropolis-Hastings algorithm, which we use for benchmarking. Exact numbers depend on observational errors and the quality of the prior. We apply our method to the Japanese Islands region where we previously constrained 3-D structure of the crust and upper mantle using full-waveform inversion with a minimum period of 15 s.
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Affiliation(s)
| | - Saule Simutė
- Institute of GeophysicsETH ZurichZurichSwitzerland
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Vallée M, Ampuero JP, Juhel K, Bernard P, Montagner JP, Barsuglia M. Observations and modeling of the elastogravity signals preceding direct seismic waves. Science 2017; 358:1164-1168. [DOI: 10.1126/science.aao0746] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2017] [Accepted: 11/02/2017] [Indexed: 11/02/2022]
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Faulting of rocks in a three-dimensional stress field by micro-anticracks. Sci Rep 2014; 4:5011. [PMID: 24862447 PMCID: PMC4034368 DOI: 10.1038/srep05011] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2013] [Accepted: 05/01/2014] [Indexed: 11/30/2022] Open
Abstract
Nucleation and propagation of a shear fault is known to be the result of interaction and coalescence of many microcracks. Yet the character and rate of the microcracks' interactions, and their dependence on the three-dimensional stress state are poorly understood. Here we investigate formation of microcracks during sandstone faulting under 3D-polyaxial stress fields by analyzing multi-stationary acoustic waveforms. We show that in a true three-dimensional stress state (a) faulting forms in a orthorhombic pattern, and (b) the emitted acoustic waveforms from microcracking carry a shorter rapid slip phase. The later is associated with microcracking that dominantly develops parallel to the minimum stress direction. Our results imply that due to inducing the micro-anticracks, the three-dimensional (3D) stress state can quicken dynamic weakening and rupture propagation by a factor of two relatively to simpler stress states. The results suggest a new nucleation mechanism of 3D-faulting with implications for earthquakes' instabilities, as well as the understanding of avalanches associated with dislocations.
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