Subduction zone | geology | turbotop.info
Margin: The Anatomy of a Subduction Zone in Space & Time. Paul Thompson, Consultant, Singapore, [email protected] Australian/Sunda Plate margin from Sumatra, where a subduction margin is generally recognized, Join ResearchGate to discover and stay up-to-date with the latest. Seismic anisotropy and heterogeneity in the Alaska subduction zone E-mail: [email protected] (YT); [email protected] (DZ) 1) and is partitioned into regions defined by the direct subduction of the Pacific Plate, the Depth distribution of the upper boundary of the subducting Pacific Plate is shown in. Subduction zones synonyms, Subduction zones pronunciation, Subduction zones translation, English dictionary definition of Subduction zones. n. A geologic .
We used the river network, topography, geomorphic features, and morphometry on a transect across the forearc to assess Quaternary crustal deformation. Uplift is not homogeneous but shows a trend of increase away from the coast. This vertical deformation is strongly influenced by subduction processes. Thus, the Papagayo River network is strongly controlled by Holocene earthquake cycle processes. This is particularly true for the southern section of the drainage basin, where E-W—striking left-lateral strike-slip faults with a vertical component offset the course of the main river.
These faults are accommodating part of the oblique plate convergence at the Mexican subduction zone. We measured the height of a series of terraces and dated quartz extracts by optically stimulated luminescence, and we calculated long-term rates of uplift ranging from 0. We discuss associations of forearc topography, faults, and long-term crustal deformation with the Cocos slab geometry, distribution of slow slip events, and earthquake-cycle deformation. The complexity of tectonic processes operating over a range of scales and the limited duration of observations often focus inquiry onto a limited space-time context that may not fully characterize or quantify tectonic variability e.
Thus, some of the most important questions concerning subduction zones remain partially addressed, such as: How is tectonic deformation distributed among various modes of fault slip, particularly for the unique conditions of subduction zones? Also, how spatially and temporally variable are megathrust slip patterns, and what processes and properties control variability? How do processes at depth and in the near surface vary? Lastly, what is the long-term expression of earthquake-cycle deformation processes observed in the geology and geomorphology of the subduction forearc?
Vertical deformation of the forearc during coseismic, postseismic, and interseismic stages of the earthquake cycle has been measured in several subduction zones along the Pacific rim, such as the Japan subduction zone Aoki and Scholz, ; Ozawa et al. Sense of vertical motion reverses between the stages of deformation i. However, some areas are more complex, such as the coast of northeastern Japan, which experienced late-interseismic and coseismic subsidence related to the A.
Vertical deformation also varies spatially across and along the forearc. Similarly, the Tohoku earthquake produced vertical coseismic and postseismic displacements across the forearc varying in magnitude and with either subsidence or uplift Ozawa et al. These examples show how the vertical motions of the coasts can differ from the classical elastic model for stress accumulation and release in the upper plate, and they raise questions regarding 1 the pattern of net deformation that is accumulated through time over several seismic cycles, and 2 the driving mechanisms.
Our goal is to understand the fundamental mechanism for uplift of the forearc inland through different time periods and to analyze individual geodetic results. Here, to address how surficial and deep processes shape the forearc, we analyze topography and fluvial terraces on the overriding plate.
An important source of information to determine vertical deformation of the forearc on time scales of to yr are uplifted fluvial terraces. The deformation of the surface of fluvial terraces, and in particular strath terraces, has been used as an indicator of displacement and long-term uplift of the upper plate in several subduction zones including the Cascadia Oregon and Washington; Personius, ; Pazzaglia and Brandon, ; Wegmann and Pazzaglia,Peruvian Pedoja et al.
Strath terraces can also be used to determine spatial variations in displacement and long-term uplift, because incision rates within a drainage basin can change both spatially and temporally Burbank et al.
Most studies on long-term vertical deformation have focused on accretion-dominated subduction zones, with few exceptions e. Late Quaternary crustal deformation was assessed through analysis of the river network, topography, and geomorphic features across a transect of the Mexican subduction zone forearc, in the Guerrero gap, and along a profile of the Papagayo River. In turn, the height was measured of a vertical sequence of terraces, and optically stimulated luminescence OSL ages were obtained from quartz extracted from fluvial sediments, to estimate long-term rates of vertical deformation.
The association amongst topography, faults, fluvial terraces, and river morphology is discussed and related to characteristics of the Cocos slab geometry, earthquake cycle deformation, and SSEs. No large thrust earthquakes have occurred in the northwestern part of the gap since the Ms 7. However, recent studies using continuous GPS observations on land and dislocation modeling suggest that the interplate coupling is broader and reaches — km inland from the trench in the northwestern section of the Guerrero seismic gap.
The subduction stress for the oblique Cocos—North America plate initiated ca. The oceanic lithosphere of the Cocos plate subducts beneath the North America continental plate with convergence rates from 6. Convergence rates between the Cocos and North America plates along the Middle America Trench and the geometry of the subducting slab in the Guerrero gap appear to control the crustal deformation in this forearc region and the earthquake thrust process.
A variety of models have been proposed for the geometry of the slab interface Kostoglodov et al. The best-fit model used in this study is based on hypocentral locations and gravity anomalies Kostoglodov et al. This coast is characterized primarily by deposition, with the landscape dominated by low deposition deltaic and alluvial plains.
Coastal lagoons are commonly separated from the ocean by barrier beaches and rocky promontories. Most of the largest river basins drain into the Pacific Ocean, eroding granitoid bodies or metamorphic rocks mainly gneissesand upstream forming deep mountain valleys with steep slopes Fig.
This area is also directly inland of the locked section of the slab of interest where the SSEs occur Figs. Although there appears to be coastal subsidence, further inland beyond the coastal-alluvial plains there are uplifted river terraces above bedrock channels of the Papagayo River. A number of E-W—trending crustal faults in the study area are expressed clearly in the landscape and river morphology; here, we focus on the topographic expression of faults and potential correlation with processes at depth.
Particularly well expressed in the landscape, downstream of the Papagayo basin, are two E-W structures that we named the Cacahuatepec fault and the Dos Arroyos fault Gaidzik et al. Deflections of the Papagayo River suggest strike-slip movement of these structures. However, an abrupt change in elevation north and south of these faults Fig.
Slickenlines and kinematic indicators recorded in the field along the trace of these crustal structures indicated a left-lateral strike-slip motion. In some locations are E-W left-lateral strike-slip meso-faults with a normal component.
It is unknown whether these faults remained inactive for the 20th and early 21st centuries. The focal mechanisms for this region encompass a relatively short period of time from to Pacheco and Singh, S1 [ footnote 1 ]. We focused on vertical displacements for both observed slow aseismic slip events and interseismic deformation e. According to these data, SSEs occurred on the subduction zone on the northwestern Guerrero seismic gap, and were observed every 3—4 yr in—,—, and Kostoglodov et al.
The down-dip slip limits for the — and for the and — SSEs were and km from the coast, respectively.
What Is a Subduction Zone?
SSEs are reported at 15—20 km depth for an up-dip slip limit in the gap area, and deeper outside the gap Radiguet et al. GPS measurements on land and modeling suggest high coupling during the interseismic period in the northwestern Guerrero seismic gap sector of the Mexican subduction zone, with a coupling ratio i.
Further inland, the coupling decreases as the slab angle approaches horizontal Radiguet et al. During the two largest SSEs — anduplift of as much as 70 mm near the coast and subsidence of 2—10 mm inland toward La Venta was reported by Vergnolle et al. Published GPS displacement data indicate that secular GPS velocity vectors are oblique to the trench and decrease by 4—5 mm across the La Venta fault i.
The decrease in velocity components across this fault suggests left-lateral motion of this fault. Here, we calculate the following geomorphic indices: We use a m-resolution DEM and digitized topographic maps scale 1: Additionally, 70 cross-sections were used through the Papagayo River valley at 1 km intervals within four defined sections of the river from La Venta to the coast Fig.
Stream Length-Gradient Index SL The stream length-gradient index SL is commonly used to evaluate effects of tectonic activity, as an indicator of zones of differential uplift in active geodynamical environments e. It is defined as: Variations in SL values are sensitive to channel slope, and are related mainly to differential uplift due to Quaternary tectonic forcing, although other factors such as Quaternary sea-level fluctuations, climate variations, and differential rock erodibility might also influence SL values e.
Generally, low values of the SL index are indicative of low uplift rates, whereas streams flowing in areas with high uplift rates show higher SL values e. The average of three measurements was used because of limited resolution of the DEM for valley width.
In that respect, it differs from the topographic residual, which is calculated by subtracting a smooth surface interpolated from the stream bottoms from a pre-incision surface Hilley and Arrowsmith, Shown as a map, the minimum bulk erosion expresses the spatial distribution of the amount of material that eroded within the drainage basin Fig. Therefore, it allows highly eroded areas to be distinguished from weakly eroded surfaces Giaconia et al.
Significant P-wave anisotropic anomalies are revealed under Alaska. The trench-parallel FVDs in the mantle wedge and subslab mantle may be caused by 3-D mantle flow that is induced by the complex geometry and strong curvature of the Pacific slab under Alaska.
The flat and oblique subduction of the Pacific slab may play a key role in forming the trench-parallel FVD under the slab. The trench-normal FVD in the subducting Pacific slab may reflect the original fossil anisotropy when the Pacific Plate was produced at the mid-ocean ridge.
Mantle processesSeismicity and tectonicsSeismic anisotropySeismic tomographySubduction zone processesVolcanic arc processes 1 Introduction Southern central Alaska is tectonically the most active region in the United States. It is situated at the receiving end of the Pacific Plate as it slides laterally past southeast Alaska and collides directly with the North American Plate across central southern Alaska and along the length of Aleutian Island Chain.
In Alaska, the plate boundary deformation is spread over a wide zone Fig. Many active volcanoes exist in the Alaskan region, but the relationship between the subducting slab and arc volcanism varies in different portions. Most of the volcanoes are distributed along the Alaska Peninsula and the chain of arc volcanoes lies above the km isobath of the subducted Pacific slab in the southwest of Mount Spurr Fig.
There exists a volcano gap in central Alaska between Mount Spurr and the Wrangell volcano region where only a yr old volcano is located at the Buzzard Creek Maars Eberhart Philips Figure 1 View large Download slide Map showing the surface topography and major tectonic features in Alaska.
The active faults are shown in solid black lines. The black box shows the present study area. Depth distribution of the upper boundary of the subducting Pacific Plate is shown in dashed contour lines. Edges of the subducted Yakutat microplate are drawn by white dashed line modified from Eberhart Philips