J. Bourgeois - Academia.edu (original) (raw)

Papers by J. Bourgeois

In 2003 we conducted detailed research on the Holocene seismotectonic evolution of Soldatskaya Ba... more In 2003 we conducted detailed research on the Holocene seismotectonic evolution of Soldatskaya Bay, Kamchatka. The bay is located between two tectonic «blocks», which constitute Kamchatsky Mys Peninsula. The southern block represents a part of the island arc front and is located at the junction of the Kurile-Kamchatka and Aleutian arcs [1]. This block is characterized by rapid uplift (up to 1 cm per year during the Late Holocene) [3, 4]. The northern block is located beyond the active subduction zone. It is characterized by rather slow differentiated movements. During our paleoseismological research in Soldatskaya Bay we have found thatthe main factors influencing its evolution in the Holocene were differentiated tectonic movements, which have been studied based on morphology, geological structure and ages of the beach ridges and marine terraces [2, 4]. Ages of the coastal landforms have been determined based on tephrochronology [5, 6]. The resulting direction of tectonic movements in Soldatskaya Bay during the last 6000 years is positive at an average rate of ~0.1 cm/yr. Tectonic movements within the interval of 6-4 ka BP are difficult to assess. We suggest that during this time some subsidence of the Holocene terrace occurred. Alternatively, there is some evidence in the North Pacific for a mid-Holocene highstand. Starting from ~4 ka BP and up to 1854 the bay has been experiencing tectonic uplift. During the period from 1950 BC to 250 AD its average rate was 0.04 cm/yr; during the period from 250 AD to 590 AD-0.23 cm/yr; and from 590 to 1854 AD-0.1 cm/yr. From 1854 to 1964 the bay experienced rapid subsidence at an average rate of 1.2 cm/yr. As we see, periods of rapid uplift in Soldatskaya Bay alternated with periods of slow uplift or even subsidence. Rates of tectonic movements were different in south and north parts of the bay. The time intervals were singled out based on dated tephra layers preserved in the coastal sections. The data obtained have allowed us to document not only differentiated tectonic movements but also large coseismic deformations related to individual strong earthquakes. In Soldatskaya Bay, abrupt vertical deformations of the surface have resulted in the formation of numerous beach ridges. The shorter the time interval we choose for our calculations, the larger the calculated amplitude of the vertical movements. This is explained by the fact that regarding Cape Kamchatskiy Soldatskaya Bay

Doklady Earth Sciences, 2008

Eos, Transactions American Geophysical Union, 2012

(e.g., Geist & Scholl, 1994; Freitag et al., 2001), the Ozernoi Peninsula remains tectonically en... more (e.g., Geist & Scholl, 1994; Freitag et al., 2001), the Ozernoi Peninsula remains tectonically enigmatic. The simplest tectonic configuration for this region incorporates the existence of a three plates, Pacific, North America and the Komandorsky Island Block (KIB) (McElfresh et al., 2002). But in fact various alternative plate models have been proposed. This area is also of interest to geoscientists because in the northwestern Pacific, there is a «dramatic shift in subduction dynamics» (Yogodzinski et al., 2001; Levin et al., 2002), where the subducting Pacific plate meets a 90-degree change in its plate boundary. The Komandorsky Basin lies north of the KIB and is characterized by transtensional and extensional elements: high heat flow, magnetic lineaments, and transcurrent faults (Baranov et al.,1991). The Ozernoi Peninsula lies on the eastern margin of the Komandorsky Basin, north of the active subduction zone. The western half of the peninsula principally comprises a Quaternary volcano, Nachikinsky. Eastern Ozernoi is undergoing active uplift and in 1969 experienced a Mw 7.7 compressional earthquake. Possible sources for this compression and uplift include 1) shear distributed from the Pacific Plate, north of the KIB (McElfresh et al., 2002), 2) convergence generated from a spreading Komandorsky Basin (Baranov et al., 1991) or 3) convergence generated by a rotating Bering Block (Mackey et al., 1997; Gordeev et al., 2001). This report is based primarily on the field season of 2003. Field techniques included physical measurement of Holocene beach profiles and transects of Pleistocene marine terraces using a digital altimeter calibrated for barometric drift and tied to local sea level corrected for tides. On the Kamchatskiy Peninsula, three Late Pleistocene and one Holocene marine terrace were mapped over more than 20 km of rocky coast north of Cape Africa. Late Quaternary uplift rates range from 0.1 to 1.0 mm/yr. On the NE part of the Ozernoi Peninsula, one Holocene and two Pleistocene marine terraces are generally present, and remnants of at least two older terraces are detectable Uplift rates range from 0.1 to 0.3 mm/yr. Based on fission-track ages of apatites, Freitag et al. (2001) report long-term (over millions of years) uplift/exhumation rates for the Kamchatskiy Peninsula of 0.2 to >1 mm/y, increasing toward the south. Our rates agree in order of magnitude, and in general trend. However, in the NE region of the peninsula, Freitag et al. report only moderate rates (0.2 mm/y), but in this same region, we documented rates from 0.1 to 1.0 mm/y, on a late Quaternary time scale (over the last half million years). Differences may be due partly to the time scale, but our study has a denser array of measurements in this northern region, so we believe we are documenting more segmentation and tilting than observed by Freitag et al. (see also Kravchynovskaya et al., this meeting). Prior to our study, no one had quantified uplift rates for the Ozernoi Peninsula. These rates are comparable to, if less than, rates on the Kamchatskiy Peninsula, a small collisional orogen. Both peninsulas show increasing uplift toward the east and south, with lowlands toward the west. Moreover, Ozernoi exhibits seismic activity consistent with a compressional regime.

Natural Hazards and Earth System Science, 2001

Along the eastern coast of Kamchatka, at a number of localities, we have identified and attempted... more Along the eastern coast of Kamchatka, at a number of localities, we have identified and attempted to assign ages to deposits of both historic and prehistoric (paleo-) tsunamis. These deposits are dated and correlated using tephrochronology from Holocene marker tephra and local volcanic ash layers. Because the historical record of earthquakes and tsunamis on Kamchatka is so short, these investigations can make important contributions to evaluating tsunami hazards. Moreover, because even the historical record is spotty, our work helps add to and evaluate tsunami catalogues for Kamchatka. Furthermore, tsunami deposits provide a proxy record for large earthquakes and thus are important paleoseismological tools. The combined, preserved record of tsunami deposits and of numerous marker tephra on Kamchatka offers an unprecedented opportunity to study tsunami frequency. Using combined stratigraphic sections, we can examine both the average frequency of events for each locality, and also changes in frequency through time. Moreover, using key marker tephra as time lines, we can compare tsunami frequency and intensity records along the Kamchatka subduction zone. Preliminary results suggest real variations in frequency on a millennial time scale, with the period from about 0 to 1000 A.D. being particularly active at some localities.

Geological Society of America Bulletin, 2001

Eos, Transactions American Geophysical Union, 1993

An earthquake with surface magnitude (M s) 7.0 occurred 100 km off the Nicaraguan coast on Septem... more An earthquake with surface magnitude (M s) 7.0 occurred 100 km off the Nicaraguan coast on September 2, 1992 (GMT). Despite its moderate size, this earthquake generated a sizable tsunami, which caused extensive damage along the coast of Nicaragua. In late September, about 170 people, mostly chil dren, were listed dead or missing; 500 were listed injured; and over 13,000 were listed homeless, with more than 1500 homes de stroyed. Damage was the most significant since the 1983 Japan Sea earthquake tsu nami, which killed 100 people in Japan. The Flores (Indonesia) earthquake and tsunami of December 12, 1992, were more destructive than the Nicaragua or Japan Sea events. Within a few days of the Nicaragua earth quake, we made a preliminary analysis of available seismic and tsunami data. Our studies indicated that this earthquake had features typical of a "tsunami earthquake," which generates an unusually large tsunami relative to earthquake magnitude [Kanamori, 1972]. It is different than a "tsunamigenic earthquake," which is any earthquake that generates a tsunami. To document this un usual tsunami, we surveyed the Nicaraguan coast in late September.

faculty.washington.edu

... DR1: Nadezhda Razhigaeva, Kirill Ganzey, Andrew Ritchie, Sergei Chirkov, Andrei Kharlamov, Do... more ... DR1: Nadezhda Razhigaeva, Kirill Ganzey, Andrew Ritchie, Sergei Chirkov, Andrei Kharlamov, Douglas Querl, Victor Kaistrenko, Misty Nikula, Mike Etnier, Natalia Slobodina, Dimitri Frolov, Nikolai Vasilenko, Ben Fitzhugh, Boris Levin, Mikhail Nosov, Molly Odell, Erik Gjesfeld ...

Tectonics, 2013

1] At the NW corner of the Pacific region, just south of the Kamchatsky Peninsula, the northern t... more 1] 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. Citation: Pedoja, K., C. Authemayou, T. Pinegina, J. Bourgeois, M. Nexer, B. Delcaillau, and V. Regard (2013), "Arccontinent collision" of the Aleutian-Komandorsky arc into Kamchatka: Insight into Quaternary tectonic segmentation through Pleistocene marine terraces and morphometric analysis of fluvial drainage, Tectonics, 32, 827-842,

In 2003 we conducted detailed research on the Holocene seismotectonic evolution of Soldatskaya Ba... more In 2003 we conducted detailed research on the Holocene seismotectonic evolution of Soldatskaya Bay, Kamchatka. The bay is located between two tectonic «blocks», which constitute Kamchatsky Mys Peninsula. The southern block represents a part of the island arc front and is located at the junction of the Kurile-Kamchatka and Aleutian arcs [1]. This block is characterized by rapid uplift (up to 1 cm per year during the Late Holocene) [3, 4]. The northern block is located beyond the active subduction zone. It is characterized by rather slow differentiated movements. During our paleoseismological research in Soldatskaya Bay we have found thatthe main factors influencing its evolution in the Holocene were differentiated tectonic movements, which have been studied based on morphology, geological structure and ages of the beach ridges and marine terraces [2, 4]. Ages of the coastal landforms have been determined based on tephrochronology [5, 6]. The resulting direction of tectonic movements in Soldatskaya Bay during the last 6000 years is positive at an average rate of ~0.1 cm/yr. Tectonic movements within the interval of 6-4 ka BP are difficult to assess. We suggest that during this time some subsidence of the Holocene terrace occurred. Alternatively, there is some evidence in the North Pacific for a mid-Holocene highstand. Starting from ~4 ka BP and up to 1854 the bay has been experiencing tectonic uplift. During the period from 1950 BC to 250 AD its average rate was 0.04 cm/yr; during the period from 250 AD to 590 AD-0.23 cm/yr; and from 590 to 1854 AD-0.1 cm/yr. From 1854 to 1964 the bay experienced rapid subsidence at an average rate of 1.2 cm/yr. As we see, periods of rapid uplift in Soldatskaya Bay alternated with periods of slow uplift or even subsidence. Rates of tectonic movements were different in south and north parts of the bay. The time intervals were singled out based on dated tephra layers preserved in the coastal sections. The data obtained have allowed us to document not only differentiated tectonic movements but also large coseismic deformations related to individual strong earthquakes. In Soldatskaya Bay, abrupt vertical deformations of the surface have resulted in the formation of numerous beach ridges. The shorter the time interval we choose for our calculations, the larger the calculated amplitude of the vertical movements. This is explained by the fact that regarding Cape Kamchatskiy Soldatskaya Bay

Doklady Earth Sciences, 2008

Eos, Transactions American Geophysical Union, 2012

(e.g., Geist & Scholl, 1994; Freitag et al., 2001), the Ozernoi Peninsula remains tectonically en... more (e.g., Geist & Scholl, 1994; Freitag et al., 2001), the Ozernoi Peninsula remains tectonically enigmatic. The simplest tectonic configuration for this region incorporates the existence of a three plates, Pacific, North America and the Komandorsky Island Block (KIB) (McElfresh et al., 2002). But in fact various alternative plate models have been proposed. This area is also of interest to geoscientists because in the northwestern Pacific, there is a «dramatic shift in subduction dynamics» (Yogodzinski et al., 2001; Levin et al., 2002), where the subducting Pacific plate meets a 90-degree change in its plate boundary. The Komandorsky Basin lies north of the KIB and is characterized by transtensional and extensional elements: high heat flow, magnetic lineaments, and transcurrent faults (Baranov et al.,1991). The Ozernoi Peninsula lies on the eastern margin of the Komandorsky Basin, north of the active subduction zone. The western half of the peninsula principally comprises a Quaternary volcano, Nachikinsky. Eastern Ozernoi is undergoing active uplift and in 1969 experienced a Mw 7.7 compressional earthquake. Possible sources for this compression and uplift include 1) shear distributed from the Pacific Plate, north of the KIB (McElfresh et al., 2002), 2) convergence generated from a spreading Komandorsky Basin (Baranov et al., 1991) or 3) convergence generated by a rotating Bering Block (Mackey et al., 1997; Gordeev et al., 2001). This report is based primarily on the field season of 2003. Field techniques included physical measurement of Holocene beach profiles and transects of Pleistocene marine terraces using a digital altimeter calibrated for barometric drift and tied to local sea level corrected for tides. On the Kamchatskiy Peninsula, three Late Pleistocene and one Holocene marine terrace were mapped over more than 20 km of rocky coast north of Cape Africa. Late Quaternary uplift rates range from 0.1 to 1.0 mm/yr. On the NE part of the Ozernoi Peninsula, one Holocene and two Pleistocene marine terraces are generally present, and remnants of at least two older terraces are detectable Uplift rates range from 0.1 to 0.3 mm/yr. Based on fission-track ages of apatites, Freitag et al. (2001) report long-term (over millions of years) uplift/exhumation rates for the Kamchatskiy Peninsula of 0.2 to >1 mm/y, increasing toward the south. Our rates agree in order of magnitude, and in general trend. However, in the NE region of the peninsula, Freitag et al. report only moderate rates (0.2 mm/y), but in this same region, we documented rates from 0.1 to 1.0 mm/y, on a late Quaternary time scale (over the last half million years). Differences may be due partly to the time scale, but our study has a denser array of measurements in this northern region, so we believe we are documenting more segmentation and tilting than observed by Freitag et al. (see also Kravchynovskaya et al., this meeting). Prior to our study, no one had quantified uplift rates for the Ozernoi Peninsula. These rates are comparable to, if less than, rates on the Kamchatskiy Peninsula, a small collisional orogen. Both peninsulas show increasing uplift toward the east and south, with lowlands toward the west. Moreover, Ozernoi exhibits seismic activity consistent with a compressional regime.

Natural Hazards and Earth System Science, 2001

Along the eastern coast of Kamchatka, at a number of localities, we have identified and attempted... more Along the eastern coast of Kamchatka, at a number of localities, we have identified and attempted to assign ages to deposits of both historic and prehistoric (paleo-) tsunamis. These deposits are dated and correlated using tephrochronology from Holocene marker tephra and local volcanic ash layers. Because the historical record of earthquakes and tsunamis on Kamchatka is so short, these investigations can make important contributions to evaluating tsunami hazards. Moreover, because even the historical record is spotty, our work helps add to and evaluate tsunami catalogues for Kamchatka. Furthermore, tsunami deposits provide a proxy record for large earthquakes and thus are important paleoseismological tools. The combined, preserved record of tsunami deposits and of numerous marker tephra on Kamchatka offers an unprecedented opportunity to study tsunami frequency. Using combined stratigraphic sections, we can examine both the average frequency of events for each locality, and also changes in frequency through time. Moreover, using key marker tephra as time lines, we can compare tsunami frequency and intensity records along the Kamchatka subduction zone. Preliminary results suggest real variations in frequency on a millennial time scale, with the period from about 0 to 1000 A.D. being particularly active at some localities.

Geological Society of America Bulletin, 2001

Eos, Transactions American Geophysical Union, 1993

An earthquake with surface magnitude (M s) 7.0 occurred 100 km off the Nicaraguan coast on Septem... more An earthquake with surface magnitude (M s) 7.0 occurred 100 km off the Nicaraguan coast on September 2, 1992 (GMT). Despite its moderate size, this earthquake generated a sizable tsunami, which caused extensive damage along the coast of Nicaragua. In late September, about 170 people, mostly chil dren, were listed dead or missing; 500 were listed injured; and over 13,000 were listed homeless, with more than 1500 homes de stroyed. Damage was the most significant since the 1983 Japan Sea earthquake tsu nami, which killed 100 people in Japan. The Flores (Indonesia) earthquake and tsunami of December 12, 1992, were more destructive than the Nicaragua or Japan Sea events. Within a few days of the Nicaragua earth quake, we made a preliminary analysis of available seismic and tsunami data. Our studies indicated that this earthquake had features typical of a "tsunami earthquake," which generates an unusually large tsunami relative to earthquake magnitude [Kanamori, 1972]. It is different than a "tsunamigenic earthquake," which is any earthquake that generates a tsunami. To document this un usual tsunami, we surveyed the Nicaraguan coast in late September.

faculty.washington.edu

... DR1: Nadezhda Razhigaeva, Kirill Ganzey, Andrew Ritchie, Sergei Chirkov, Andrei Kharlamov, Do... more ... DR1: Nadezhda Razhigaeva, Kirill Ganzey, Andrew Ritchie, Sergei Chirkov, Andrei Kharlamov, Douglas Querl, Victor Kaistrenko, Misty Nikula, Mike Etnier, Natalia Slobodina, Dimitri Frolov, Nikolai Vasilenko, Ben Fitzhugh, Boris Levin, Mikhail Nosov, Molly Odell, Erik Gjesfeld ...

Tectonics, 2013

1] At the NW corner of the Pacific region, just south of the Kamchatsky Peninsula, the northern t... more 1] 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. Citation: Pedoja, K., C. Authemayou, T. Pinegina, J. Bourgeois, M. Nexer, B. Delcaillau, and V. Regard (2013), "Arccontinent collision" of the Aleutian-Komandorsky arc into Kamchatka: Insight into Quaternary tectonic segmentation through Pleistocene marine terraces and morphometric analysis of fluvial drainage, Tectonics, 32, 827-842,