Geochemistry of Recent oxic and anoxic marine sediments: Implications for the geological record

Detailed analysis of Global Positioning System data from Japan's Geospatial Information Authority network provides a record of coseismic and postseismic slip distribution on the megathrust fault where the magnitude-9.0 Tohoku-Oki earthquake occurred on 11 March 2011. The coseismic slip area stretches some 400 kilometres along the Japan trench, matching the area of the preseismic locked zone. Afterslip is now overlapping the coseismic slip area and expanding into the surrounding regions. The authors conclude that such geodetic data could help to improve the forecasting of earthquake potential along other subduction zones. In the accompanying News & Views, Jean-Philippe Avouac discusses current models for assessing seismic hazard. Most large earthquakes occur along an oceanic trench, where an oceanic plate subducts beneath a continental plate. Massive earthquakes with a moment magnitude, Mw, of nine have been known to occur in only a few areas, including Chile, Alaska, Kamchatka and Sumatra. No historical records exist of a Mw = 9 earthquake along the Japan trench, where the Pacific plate subducts beneath the Okhotsk plate, with the possible exception of the ad 869 Jogan earthquake1, the magnitude of which has not been well constrained. However, the strain accumulation rate estimated there from recent geodetic observations is much higher than the average strain rate released in previous interplate earthquakes2,3,4,5,6. This finding raises the question of how such areas release the accumulated strain. A megathrust earthquake with Mw = 9.0 (hereafter referred to as the Tohoku-Oki earthquake) occurred on 11 March 2011, rupturing the plate boundary off the Pacific coast of northeastern Japan. Here we report the distributions of the coseismic slip and postseismic slip as determined from ground displacement detected using a network based on the Global Positioning System. The coseismic slip area extends approximately 400 km along the Japan trench, matching the area of the pre-seismic locked zone4. The afterslip has begun to overlap the coseismic slip area and extends into the surrounding region. In particular, the afterslip area reached a depth of approximately 100 km, with Mw = 8.3, on 25 March 2011. Because the Tohoku-Oki earthquake released the strain accumulated for several hundred years, the paradox of the strain budget imbalance may be partly resolved. This earthquake reminds us of the potential for Mw ≈ 9 earthquakes to occur along other trench systems, even if no past evidence of such events exists. Therefore, it is imperative that strain accumulation be monitored using a space geodetic technique to assess earthquake potential.

Coseismic and postseismic slip of the 2011 magnitude-9 Tohoku-Oki earthquake

Geophysical observations from the 2011 moment magnitude (M_w) 9.0 Tohoku-Oki, Japan earthquake allow exploration of a rare large event along a subduction megathrust. Models for this event indicate that the distribution of coseismic fault slip exceeded 50 meters in places.
 Sources of high-frequency seismic waves delineate the edges of the
 deepest portions of coseismic slip and do not simply correlate with the
 locations of peak slip. Relative to the M_w 8.8 2010 Maule, Chile
 earthquake, the Tohoku-Oki earthquake was deficient in high-frequency
 seismic radiation-a difference that we attribute to its relatively
 shallow depth. Estimates of total fault slip and surface secular strain
 accumulation on millennial time scales suggest the need to consider the
 potential for a future large earthquake just south of this event.

https://science.sciencemag.org/content/sci/332/6036/1421.full.pdf

The 2011 Magnitude 9.0 Tohoku-Oki Earthquake: Mosaicking the Megathrust from Seconds to Centuries

https://earthweb.ess.washington.edu/tsunami2/deposits/downloads/recommendedreading/Morton_SedGeoAcpt_tsunamiVstorm_Deposits.pdf

Physical criteria for distinguishing sandy tsunami and storm deposits using modern examples

The nitrogen-isotope record preserved in Southern Ocean sediments, along with several geochemical tracers for the settling fluxes of biogenic matter, reveals patterns of past nutrient supply to phytoplankton and surface-water stratification in this oceanic region. Areal averaging of these spatial patterns indicates that reduction of the CO2 ‘leak’ from ocean to atmosphere by increased surface-water stratification south of the Polar Front made a greater contribution to the lowering of atmospheric CO2 concentration during the Last Glacial Maximum than did the increased export of organic carbon from surface to deep waters occurring further north.

Contribution of Southern Ocean surface-water stratification to low atmospheric CO 2 concentrations during the last glacial period

The fore-arc region of northeast Japan is an area of extensive seismic activity and tsunami generation. On July 13, 869 a tsunami triggered by a large-scale earthquake invaded its coastal zones, causing extensive deposition of well-sorted fine sand over the coastal plains of Sendai and S ma. Sediment analysis and hydrodynamic simulation indicate that the tsunami inferred to be triggered by a magnitude 8.3 earthquake spread more than 4 km inland then coast. We postulate that the sand layer was developed by the tsunami ’ s first wave. Traces of largescale invasion by old tsunami as recorded in the coastal sequences of the Sendai plain show about a 1000-year reoccurrence interval. We suggest that the J gan tsunami was much larger than tsunami generated by normal earthquakes in the subduction interface. o o o o

/pdf/the-869-jogan-tsunami-deposit-and-recurrence-interval-of-ye9qokhey3.pdf

The 869 Jogan tsunami deposit and recurrence interval of large-scale tsunami on the Pacific coast of northeast Japan

Distribution, origin and transport process of boulders deposited by the 2004 Indian Ocean tsunami at Pakarang Cape, Thailand

Tsunami deposits in a lacustrine sequence of the Sanriku coast, northeast Japan

The Hellenic arc is a terrane of extensive Quaternary volcanism One of the main centers of explosive eruptions is located on Thera (Santorini), and the eruption of the Thera volcano in late Minoan time (1600–1300 BC) is considered to have been the most significant Aegean explosive volcanism during the late Holocene The last eruptive phase of Thera resulted in an enormous submarine caldera, which is believed to have produced tsunamis on a large scale Evidence suggesting seawater inundation was found previously at some archaeological sites on the coast of Crete; however, the cause of the tsunami and its effects on the area have not been well understood On the Aegean Sea coast of western Turkey (Didim and Fethye) and Crete (Gouves), we have found traces of tsunami deposits related to the Thera eruption The sedimentological consequences and the hydraulics of a Thera-caused tsunami indicate that the eruption of Thera volcano was earlier than the previous estimates and the tsunami did not have disruptive influence on Minoan civilization

Koji Minoura

Papers

The 869 Jogan tsunami deposit and recurrence interval of large-scale tsunami on the Pacific coast of northeast Japan

Distribution, origin and transport process of boulders deposited by the 2004 Indian Ocean tsunami at Pakarang Cape, Thailand

Tsunami deposits in a lacustrine sequence of the Sanriku coast, northeast Japan

Discovery of Minoan tsunami deposits

Palaeoenvironmental history of Lake Baikal during the last 23000 years