Active blind thrusts beneath the Tokyo metropolitan area: Seismic hazards and inversion tectonics

Ishiyama, Tatsuya; Satō, Hiroshi; Kato, Naoko; Nakayama, Tsuneyoshi; Abe, Susumu

doi:10.1002/grl.50487

Cited by 10 publications

(4 citation statements)

References 18 publications

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“…For example, a statistical analysis of crustal earthquakes in New Zealand has shown that more than half of the historical large earthquakes ruptured along previously unidentified faults 1 . Further cryptic and partly hidden active faults have also been documented at the Cascadia 68 , 69 margin as well as in the Kanto region of Japan 70 , and similar conditions are likely to exist along other subduction zones. We conclude that regional-scale acquisition of LiDAR topography, combined with the quantitative analysis of off-fault and on-fault geomorphic markers and geodetic data is a promising way forward that will ultimately improve our knowledge of the location, deformation mechanisms, and recurrence time of hitherto unidentified seismogenic faults at convergent margins.…”

Section: Resultsmentioning

confidence: 84%

The cryptic seismic potential of the Pichilemu blind fault in Chile revealed by off-fault geomorphology

Jara‐Muñoz

Melnick

et al. 2022

Nat Commun

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The first step towards assessing hazards in seismically active regions involves mapping capable faults and estimating their recurrence times. While the mapping of active faults is commonly based on distinct geologic and geomorphic features evident at the surface, mapping blind seismogenic faults is complicated by the absence of on-fault diagnostic features. Here we investigated the Pichilemu Fault in coastal Chile, unknown until it generated a Mw 7.0 earthquake in 2010. The lack of evident surface faulting suggests activity along a partly-hidden blind fault. We used off-fault deformed marine terraces to estimate a fault-slip rate of 0.52 ± 0.04 m/ka, which, when integrated with satellite geodesy suggests a 2.12 ± 0.2 ka recurrence time for Mw~7.0 normal-faulting earthquakes. We propose that extension in the Pichilemu region is associated with stress changes during megathrust earthquakes and accommodated by sporadic slip during upper-plate earthquakes, which has implications for assessing the seismic potential of cryptic faults along convergent margins and elsewhere.

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Section: Resultsmentioning

confidence: 84%

The cryptic seismic potential of the Pichilemu blind fault in Chile revealed by off-fault geomorphology

Jara‐Muñoz

Melnick

et al. 2022

Nat Commun

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“…Such work may reveal the magnitudes and recurrence intervals of paleoearthquakes and allow a detailed assessment of the seismic hazards posed by these poorly understood thrust faults [Liu-Zeng et al, 2009]. Such work has been done for other active structures in convergent settings worldwide, such as in Los Angeles [Shaw and Shearer, 1999;Dolan et al, 2003] and Tokyo [Ishiyama et al, 2013]. Moreover, further refinement of 3-D structural models and community fault models for this region [Plesch et al, 2007] will be important in assessing seismic hazards.…”

Section: Discussionmentioning

confidence: 99%

Quaternary activity of the range front thrust system in the Longmen Shan piedmont, China, revealed by seismic imaging and growth strata

Liu‐Zeng

Jia

et al. 2016

Tectonics

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Reliable estimates of Quaternary or Cenozoic upper crustal shortening in the Longmen Shan fold‐and‐thrust belt are rare. In this paper, we report on our use of high‐resolution 2‐D and 3‐D seismic reflection profiles at various scales, together with borehole data, to investigate the structural geometry of the Longmen Shan piedmont. The results reveal a thrust system beneath the Longmen Shan, termed the range front thrust system, which consists of the range front blind thrust and its upward splay faults. Moreover, on these faults we identified growth strata that provide an excellent opportunity for assessing the activity of this thrust system. Analyses of the growth strata reveal early to late Pleistocene activity on the range front blind thrust, with minimum dip slip and horizontal shortening rates of 1.1 ± 0.2 mm/yr and ~1 mm/yr. Accordingly, the maximum accumulated slip on the range front blind thrust is calculated to be 7.5 ± 0.3 km in the Longmen Shan. Using the new horizontal shortening rate and other published data, we also estimated that the long‐term shortening rate across the Longmen Shan fold‐and‐thrust belt is 1–3 mm/yr, which is comparable to the short‐term GPS rate. The similarity of these rates suggests that the Longmen Shan attained a steady state condition over the past 2 Myr. An additional highlight of our results is that we show Quaternary activity around the Tibetan Plateau to have been nearly synchronous in different regions, including in the Longmen Shan, the Himalayas, the western Kunlun Shan, and the northern Qilian Shan.

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“…In particular, large earthquakes with recurrence intervals of several centuries to a few millennia can be missed by the use of temporally short datasets. As a consequence, geological records on centennial to millennial temporal scales and highresolution near-surface stratigraphic studies are crucial to understand the occurrence of large, but infrequent, seismic events (Begg et al, 1993;Sinha et al, 2005;Ishiyama et al, 2007Ishiyama et al, , 2013Dura et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Deformation patterns of upper Quaternary strata and their relation to active tectonics, Po Basin, Italy

et al. 2020

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Despite increased application of subsurface datasets below the limits of seismic resolution, reconstructing near-surface deformation of shallow key stratigraphic markers beneath modern alluvial and coastal plains through sediment core analysis has received little attention. Highly resolved stratigraphy of Upper Pleistocene to Holocene (Marine Isotope Stage 5e to Marine Isotope Stage 1) alluvial, deltaic and coastal depositional systems across the southern Po Plain, down to 150 m depth, provides an unambiguous documentation on the deformation of previously flat-lying strata that goes back in time beyond the limits of morphological, historical and palaeoseismic records. Five prominent key horizons, accurately selected on the basis of their sedimentological characteristics and typified for their fossil content, were used as highly effective stratigraphic markers (M1 to M5) that can be tracked for tens of kilometres across the basin. A facies-controlled approach tied to a robust chronology (102 radiocarbon dates) reveals considerable deformation of laterally extensive nearshore (M1), continental (M2 and M3) and lagoon (M4 and M5) marker beds originally deposited in a horizontal position (M1, M4 and M5). The areas where antiformal geometries are best observed are remarkably coincident with the axes of buried ramp anticlines, across which new seismic images reveal substantially warped stratal geometries of Lower Pleistocene strata. The striking spatial coincidence of fold crests with the epicentres of historic and instrumental seismicity suggests that deformation of marker beds M1 to M5 might reflect, in part at least, syntectonically generated relief and, thus, active tectonism. Precise identification and lateral tracing of chronologically constrained stratigraphic markers in the 14 C time window through combined sedimentological and palaeoecological data may delineate late Quaternary subsurface stratigraphic architecture at an unprecedented level of detail, outlining cryptic stratal geometries at the sub-seismic scale. This approach is highly reproducible in tectonically active Quaternary depositional systems and can help to assess patterns of active deformation in the subsurface of modern alluvial and coastal plains worldwide.

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Active blind thrusts beneath the Tokyo metropolitan area: Seismic hazards and inversion tectonics

Cited by 10 publications

References 18 publications

The cryptic seismic potential of the Pichilemu blind fault in Chile revealed by off-fault geomorphology

The cryptic seismic potential of the Pichilemu blind fault in Chile revealed by off-fault geomorphology

Quaternary activity of the range front thrust system in the Longmen Shan piedmont, China, revealed by seismic imaging and growth strata

Deformation patterns of upper Quaternary strata and their relation to active tectonics, Po Basin, Italy

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