A Comprehensive Stress Drop Map From Trench to Depth in the Northern Chilean Subduction Zone

Folesky, J.; Pennington, C. N.; Kummerow, J.; Hofman, L. J.

doi:10.1029/2023jb027549

Cited by 5 publications

(10 citation statements)

References 72 publications

(174 reference statements)

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“…Especially at the plate interface, the decreased roughness of the event rupture surfaces from repeated slip should result in comparatively low stress drop ruptures 4 . There is no pronounced depth dependence for interface event median stress drop 15 . Also, one should note that in principle at the plate interface a substantial variability of stress drop is observed, i.e., there exist low and high stress drop regions, indicative for the large heterogeneity of the interface rupture conditions (Fig.…”

Section: Discussionmentioning

confidence: 90%

“…Database for this work is the recent stress drop map from Folesky et al 2024 15 (Fig. 1 ), who employed the spectral decomposition method 11 , 13 , 17 and the spectral ratio method 9 , 12 , 18 to compute a comprehensive set of 51,510 stress drop estimates for northern Chile.…”

Section: Resultsmentioning

confidence: 99%

“…A clear gap (F) separates this band from its southern part, where high stress drop values are found 20 km further east and extending to much greater depth. Please note that despite all efforts to improve robustness, stress drop values may be biased by inaccuaries in the velocity model, change of the shear wave velocity to rupture velocity ratio or changing rupture dircetivity 15 , 30 .…”

Section: Resultsmentioning

confidence: 99%

“…Also note, that this work does not consider temporal variability of stress drop inflicted by the megathrust events, as they pose an additional subject and will be studied in a separate paper. According to Folesky et al 2024 15 , there does not appear to be a long term offset in stress drop induced by the events but only a short (few days) increase of stress drop after a big event, localized to the direct rupture vicinity. The intermediate depth seismicity appears not affected.…”

Section: Discussionmentioning

confidence: 97%

“…Following this idea, a recently published comprehensive stress drop catalog from northern Chile 15 is combined with measurements of b-values and the magnitude distribution computed from a recent seismicity catalog for the northern Chilean subduction zone. The catalog covers more than 180,000 events over 15 years of record 16 , which means that it includes the 2007 MW7.7 Tocopilla event and the 2014 MW8.1 Iquique event along with their fore- and aftershock seismicity.…”

Section: Introductionmentioning

confidence: 99%

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Different earthquake nucleation conditions revealed by stress drop and b-value mapping in the northern Chilean subduction zone

Folesky

2024

Sci Rep

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Stress drop is an earthquake property indicative for the characteristic relation of slip to fault dimension. It is furthermore affected by fault strength, fault topography, the presence of fluids, rupture size, slip, and velocity. In this article, the stress drop image of an entire subduction zone, namely for the seismically highly active northernmost part of Chile, is combined with mapped b-values and their corresponding magnitude distribution in order to better constrain the conditions under which earthquakes of different provenances may nucleate. The underlying recent earthquake catalog contains over 180,000 events, covering 15 years of seismicity, from which more than 50,000 stress drop estimates were computed. Their spatial average segments the subduction zone into different parts, i.e., average stress drop between seismotectonic areas is different, although this difference is small compared to the natural scatter of stress drop values. By considering stress drop variations, b-value map, magnitude distribution, and thermal models, candidate earthquake nucleation mechanisms are identified which can explain the observed distributions. This is done for two exemplary regions: (1) The plate interface, where principally lower stress drop events are found, while at the same time a high spatial heterogeneity of stress drop values is observed. This indicates relatively smooth or lubricated rupture surfaces, and locally it suggests the existence of alternating regions controlled by strong asperities, weaker material, or creep. (2) The highly active intermediate depth (ID) seismicity region, where the variation of stress drop and b-value point to a gradual change of nucleation mechanism from dehydration embrittlement at the top of the ID cloud, over dehydration driven stress transfer in its central part, to thermal runaway shear mechanisms at its bottom. In both cases, the combination of stress drop and b-value distribution helps to better understand the origin and the differences of the observed seismicity.

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Section: Discussionmentioning

confidence: 90%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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Different earthquake nucleation conditions revealed by stress drop and b-value mapping in the northern Chilean subduction zone

Folesky

2024

Sci Rep

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Stress drops of intermediate-depth intraslab earthquakes beneath Tohoku, northern Japan

Kita,

Shiina,

Houston

et al. 2024

Earth Planets Space

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We calculated stress drops for 2875 small intraslab earthquakes at intermediate depths beneath Tohoku, Japan. We applied an S-coda-wave spectral ratio method to almost 900,000 event pairs. Detailed velocity values for the oceanic crust (OC) were adopted from previous observational studies. The median stress drops in the OC are about half those in the oceanic mantle (OM). The median stress drop for earthquakes in the OC decreases from depths of 70 to 120 km and increases from 120 to 170 km. Our preferred interpretation is that the rigidity in the OC decreases and then increases with depth due to combined effects of the dehydration associated with the eclogite formation and the increasing temperature with depth. These depth variations are consistent with results of a similar study beneath Hokkaido. The median stress drops in the oceanic plate beneath Tohoku are generally smaller than those beneath Hokkaido. Previous studies imaging the seismic structure at shallow depths and b-value analyses of intraslab earthquakes indicate that the near-trench region of the oceanic plate off Tohoku is more hydrated than that off Hokkaido. Taken together, these results suggest that differences in the degree of hydration of the oceanic plate in the near-trench regions could produce the different behaviors of stress drops of intermediate-depth earthquakes observed in Tohoku and Hokkaido. Graphical Abstract

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Time-Dependent Stress Drop Variations After Large Earthquakes Along the North Chilean Megathrust

Folesky,

Kummerow

2024

Bulletin of the Seismological Society of America

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We observe a time dependence of the median stress drop in spatiotemporal proximity of large earthquakes. The median stress drop of the early aftershock seismicity is elevated for only a few days after the mainshocks and then rapidly falls back to the long-term average. This short-term variation has remained largely unnoticed by previous studies, presumably due to their usually low temporal resolution. Our study uses a recent extensive stress drop catalog, which contains more than 51,000 events from northern Chile. It includes observations from three Mw>7 megathrust earthquakes, namely the 2007 Mw 7.7 Tocopilla earthquake, the 2014 Mw 8.1 Iquique earthquake, and its largest Mw 7.6 aftershock, as well as another eleven Mw>6 earthquakes. A detailed analysis reveals that the elevated stress drop is not primarily linked to an increase of seismic moment during the early aftershock phase but is rather attributable to higher measured corner frequencies in the corresponding time interval. We propose two possible explanations: (1) The high stress changes induced by the mainshock allow failure of strong structures at or adjacent to the main rupture area, which produces higher stress drop events. After a few days, afterslip activity has reduced the in situ stresses and thereby the failure potential of the stronger regions. (2) The mainshock disturbs the fluid-sealing plate interface, allowing overpressured fluids to escape, exhibiting the so-called fault-valve behavior. The effect appears to persist only for several days until the sealing effect is restored and average stress drop levels are recovered.

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A Comprehensive Stress Drop Map From Trench to Depth in the Northern Chilean Subduction Zone

Cited by 5 publications

References 72 publications

Different earthquake nucleation conditions revealed by stress drop and b-value mapping in the northern Chilean subduction zone

Different earthquake nucleation conditions revealed by stress drop and b-value mapping in the northern Chilean subduction zone

Stress drops of intermediate-depth intraslab earthquakes beneath Tohoku, northern Japan

Time-Dependent Stress Drop Variations After Large Earthquakes Along the North Chilean Megathrust

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