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

Abstract

International audienceKamchatsky 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 profiles and quantified vertical deformation on single profiles 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

Coastal staircase sequences reflecting sea-level oscillations and tectonic uplift during the Quaternary and Neogene

“…The Holocene uplift rates are usually 2-3 times higher than Pleistocene rates (see Lajoie, 1986, his Figure 6.11), and at some sites even an order of magnitude higher (Pinegina et al, 2010;Pedoja et al, 2013a;Pinegina et al, 2013). However, such changes are not so apparent in other areas (e.g.…”

“…First, Holocene and MIS 5e uplift rates are widely discrepant in some zones affected by deformation associated with great earthquakes (e.g. Lajoie, 1986;Ota and Yamaguchi, 2004;Pinegina et al, 2010Pinegina et al, , 2013. Second, only a few paleocoasts have been correlated to the MIS 3 interval.…”

The 1997 Kronotsky earthquake and tsunami and their predecessors, Kamchatka, Russia

“…Changes in elevation relative to sea level are quantified by determining the age and elevation of the lowest former soil horizon above marine sand in any excavation ( Fig. S5; as in Pinegina et al, 2013). For the case herein, reconstructing less than 2000 years of coastal history, our calculated changes in relative sea level are due to active tectonics, not eustatic or regional sea-level fluctuation.…”

“…While we cannot typically reconstruct profiles that have been changed by erosion, we can reconstruct profile progradation (building seaward), which affects profile width. Our method uses preserved tephra as discussed, for example, in Pinegina et al (2013) and MacInnes et al (2016), as summarized in Fig. S5.…”

“…4) maintain lower elevations (< 4 m) over much of their distance, though both reach elevations of more than 6 m above sea level. The other five profiles rise, typically in sharp steps indicative of Holocene uplift events (as in Pinegina et al, 2013), reaching typical maximum levels of 8-10 m (Fig. 4).…”