A nexus of plate interaction: Vertical deformation of Holocene wave-built terraces on the Kamchatsky Peninsula (Kamchatka, Russia)

Kamchatsky Peninsula lies within a complex meeting place of tectonic plates, in particular, the orthogonal interaction of the west-moving Komandorsky Island block with mainland Kamchatka. Examining the Holocene history of vertical deformation of marine wave-built terraces along the peninsular coast, we differentiated tectonic blocks undergoing uplift and tilting separated by zones of stable or subsided shorelines. We analyzed ~200 excavations along >30 coastal profi les and quantifi ed vertical deformation on single profi les as well as along the coast using paleoshorelines dated with marker tephras. For the past ~2000 yr, the average rates of vertical deformation range from about –1 to +7 mm/yr. Uplift patterns are similar to those detected from historical leveling and from mapping of the stage 5e Quaternary marine terrace (ca. 120 ka). Average vertical deformation in the Holocene is highest for the shortest studied time period, from ca. A.D. 250 to 600, and it is several times faster than rates for marine oxygen isotope stage (MIS) 5e terraces. Vertical displacements observed along the coast are most likely coseismic and probably have included subsidence as well as uplift events. Because subsidence is generally associated with erosion, almost surely more prehistoric large earthquakes occurred than are recorded as topographic steps in these terraces. We suggest that the distribution of coastal uplift and subsidence observed along the Kamchatsky Peninsula coastline is qualitatively explained by the squeezing of the Kamchatsky Peninsula block between the Bering and Okhotsk plates, and the Komandorsky Island block

Active Tectonics and Geomorphology of the Kamchatsky Bay Coast in Kamchatka

Kamchatsky Bay is the northernmost bay at the Pacific Kamchatka coast. It is located at the junction between the Kamchatka segment of the Pacific subduction zone and the dextral transform fault of the western Aleutians. The combination of the subduction and collision processes in this region results in the unique set of tectonic controls influencing its geological and geomorphological evolution. The Kamchatka River estuarine area is located on the northern coast of Kamchatsky Bay. The modern Kamchatka River valley, its estuary, and an aggradation marine terrace some 30 km long and up to 5 km wide were formed in this area during the Holocene. A vast area in the rear part of the terrace and in the Stolbovskaya lowlands is now occupied by the peats deposited directly above lacustrine–lagoonal and fluvial facies. These aggradational landforms record traces of tsunamis and vertical coseismic deformations associated with great subduction earthquakes, as well as strikeslip and thrust faulting associated with the collision. The results indicate that the average recurrence interval for major tsunamis in the Kamchatsky Bay is 300 years. The recurrence interval on individual fault zones associated with the collision between the western Aleutian and Kamchatka arcs is a few thousand years for earthquakes of magnitude between 7 and 7.5. For the entire region, the recurrence interval for major crustal earthquakes associated with motions along faults may be equal to a few hundred years, which is comparable with that for subductionzone earthquakes

Holocene tsunamis in the southwestern Bering Sea, Russian Far East, and their tectonic implications

The Bering Sea coast of Kamchatka overlies a boundary between the proposed Okhotsk and Bering blocks, or (micro)plates, of the North American plate in the Russian Far East. A history of tsunamis along this coast for the past 4000 yr indicates that the zone north of the Kuril-Kamchatka subduction zone produces tsunamigenic earthquakes every few centuries. Such a record is consistent with convergence of the proposed Okhotsk and Bering blocks along the Bering Sea coast of Kamchatka. A tsunami deposit from the 1969 Mw 7.7 Ozernoi earthquake helps us interpret older tsunami deposits. Newly studied tephra layers from Shiveluch volcano as well as previously established marker tephra layers in northern Kamchatka provide age control for historic and prehistoric tsunami deposits. Based on >50 measured sections along 14 shoreline profiles, tsunami-deposit frequencies in the southwestern Bering Sea are about five per thousand years for tsunamis generated north of the Kuril-Kamchatka trench

Expeditionary research on the Kronotsky Peninsula

The sublatitudinal active fault on the Kronotsky Peninsula (Kamchatka) has been studied. The deformations of the Holocene soil-pyroclastic cover opened by the trench indicate reverse vertical movements along the fault plane. The northern fault side is relatively downthrown. Evidence for a horizontal component is less certain because of the small number of geomorphologic references, but together they indicate that it is left-latetal. The average rate of strike-slip movements can be estimated to be of the order of 10 mm per year. Two explanations for the existence of a arc-normal active fault seem possible: the fault as part of a transform left-lateral horizontal flexure connecting the collisional part of Kamchatka with its transverse extension-prone part, and the fault as a result of clockwise rotation of the Kronotsky Peninsula block. The second option implies that the Pacific plate is being pushed under Kamchatka at an angle to it and seems less likely

"Arc-continent collision" of the Aleutian-Komandorsky arc into Kamchatka: Insight into Quaternary tectonic segmentation through Pleistocene marine terraces and morphometric analysis of fluvial drainage

At the NW corner of the Pacific region, just south of the Kamchatsky Peninsula, the northern tip of the Pacific plate subduction and associated volcanic arc interacts with the western end of the Aleutian-Komandorsky dextral transform plate boundary and associated arc. Study of both Holocene and Pleistocene sequences of uplifted marine terraces and also of fluvial drainage patterns on the Kamchatsky Peninsula allows us to highlight active tectonics produced by complex plate interaction. Our results show that the central eastern coast of the peninsula is currently divided into four different zones consisting in uplifted blocks associated with various uplift rates in front of a fold-and-thrust zone to the west. Our main tectonic benchmark—the altitude of the shoreline correlated to the Last Interglacial Maximum (Marine Isotopic Stage 5e)—yields late Pleistocene uplift rates ranging from 0.2 to 2.74 mm/yr. One of the main active faults bounding the coastal blocks is dextral and is interpreted as a prolongation of an offshore fault of the Aleutian-Komandorsky dextral transform plate boundary. We suggest that structures on the Kamchatsky Peninsula accommodate a part of the transform motion, but that mainly, the arc-continent collision of the Aleutian arc against Kamchatka produces a “bulldozer” effect on the Kamchatsky Peninsula