les failles actives - .les failles actives identification - images satellitaires - terrain...

Download Les failles actives - .Les failles actives Identification - images satellitaires - terrain Fonctionnement

If you can't read please download the document

Post on 13-Sep-2018

213 views

Category:

Documents

0 download

Embed Size (px)

TRANSCRIPT

  • Les failles actives

    Identification - images satellitaires - terrain

    Fonctionnement - vitesse moyenne - cycle sismique

  • 124!W

    124!W

    122!W

    122!W

    120!W

    120!W

    118!W

    118!W

    116!W

    116!W

    32!N 32!N

    34!N 34!N

    36!N 36!N

    38!N 38!N

    40!N 40!N

    Sismicit de la Californie (1973-2004)

    La faille de San Andreas n'est pas active ???

  • Ruptures de surface du sisme de Kokoxili (2001, Mw = 7.9)

    Une faille active modifie le paysage

  • Combinaison dimages SPOT (10 m) et IKONOS (! 1 m)

    (Documents Y. Klinger, Tectonique IPGP)

    Faille du Kunlun

  • Formation des facettes triangulaires

  • Versant ouest contrl par une faille Versant est contrl par l'rosion

  • Tanghenanshan

    Topographienumrique

    Image Landsat

  • Tanghenanshan

    Topographie + Image satellitaire

    SW NE

    Yves Gaudemer, 2005

  • SW NE

    Van der Woerd et al. 2003

    Plis actifs

  • Meyer 1991

    Shibaocheng

  • Photo P. Tapponnier

  • 120 km

    Dcalage du Fleuve Jaune (Huanhe) par la

    faille de Haiyuan

  • Comment fonctionne une faille ?

  • Si la faille fonctionne rgulirement, avec un sisme caractristique, le temps de

    rcurrence T de celui-ci est simplement :T = U/V

    o U est le dplacement cosismiqueet V est la vitesse de glissement sur la faille.

    Exemple :M = 8, U = 10 m, V = 1 cm/an > T = 1000 ans

    Dterminer U et V

  • At six different sites we dated as many as 93 quartz pebblesand 22 organic samples to constrain the ages of the cumulativeoffsets of 11 distinct morphological markers. The large numberof samples is paramount in obtaining statistically meaningfulcosmogenic ages, and in identifying clearly and discardingoutliers on any given terrace. Several independent values of

    both the marker ages and slip-rates, based either on cosmo-genic or 14C dating, are consistent with one another at each siteand from site-to-site (Fig. 31), giving us confidence in individualrate determinations. Overall, our estimate of the slip-rate isdetermined within an uncertainty of t2.0 mm yrx1, and theaverage value of 11.5 mm yrx1 is robust (Fig. 31).For offset risers, the ages we take, and hence the slip-rates,

    depend on field interpretation regarding the terraces (strathin general, fill in one case), the nature of which may vary fromsite-to-site or at a given site. An end-member scenario, con-sidered highly unlikely, is that the ages of all riser offsets arethose of upper terraces. Slip-rates derived in this scenarioare y7 mm yrx1. In view of geological evidence, we believe7 mm yrx1 to be implausibly small. Nonetheless, this value isgreater than the rate inferred from two epoch remeasurementsof the few extant GPS stations north and south of the KunlunFault (Chen et al. 2000). Until a denser and longer GPS surveyis undertaken, slip-rates based on this technique should beregarded as preliminary.Our average rate value of 11.6t0.8 mm yrx1 in Xidatan

    Dongdatan (Fig. 15), which is based only on cosmogenicdating of offset terrace risers, is consistent with those derivedfrom other geological studies with different dating tech-niques. Zhao et al. (1994) and Zhao (1996), in particular,documented 10 offsets of gullies and terrace risers in Xidatan,ranging from 10 to 152 m, and retrieved seven TL or 14Cages, ranging from 2.14 to 12.0 kyr BP, with uncertainties of69 per cent. From this, they derived a Holocene slip-rateof about 11.5 mm yrx1. Unfortunately, without error estimateson the offsets, the uncertainty on that rate cannot be assessed.The average Quaternary rate estimated by Kidd & Molnar(1988) (1020 mm yrx1), loosely brackets both our values andthose of Zhao et al. In a strict sense, however, it cannot besimply compared with either, because it corresponds to a muchlonger time-span. Recall that the long-term rate of Kidd &Molnar (1988) is deduced from the separation between LowerPleistocene moraines containing boulders of pyroxenite, southand east of the Kunlun Pass, and their presumed source area,30 km to the west, in the mountains north of the fault. Thefactor of two in the estimate comes chiefly from the largeuncertainty in the age of the lake-beds that overlie the moraine(2.81.5 Ma) (Kidd & Molnar 1988; Qian et al. 1982; Wu et al.1982). To this uncertainty on the age, one should also probablyadd a y30 per cent error on the offset, due to poor definitionof the eastern piercing point (Kidd & Molnar 1988: Fig. 6).Hence, while it is interesting to note that there is no first-order discrepancy between the loosely constrained, averageQuaternary rate (Kidd & Molnar 1988) and the Holocene slip-rates derived from 14C, TL or cosmogenic dating, kinematicmodels of the current tectonics of northeast Tibet making useof the latter rates will be more precise.

    5.2 Climatic origin of the morphology

    Along the XidatanDongdatan valleys, the relatively smallnumber of terrace levels (about seven, Fig. 5) found along mostof the streams implies a relatively uniform morphologicalresponse on a regional scale. It seems that most of the streamsemplaced terraces at discrete, comparable times. Not all thestreams deposited all the terrace levels identified, however. Thevariable distribution of terraces along the different streamsis thus probably due to local conditions in each watershed.

    Figure 28. View, looking west, along fault strike of the shutter ridgewest of Maqen (see Fig. 27b for location). The stream incision acrossthe ridge reveals several tens of metres of thick, vertical gouge.

    Figure 29. View of the offset LGMmoraine ridge and T3 terrace level,abandoned after 11 156t157 yr BP.

    Figure 30. View, looking south, of a small gully offset by the KunlunFault. The offset, probably resulting from only one large earthquake, isabout 12 m.

    382 J. Van Der Woerd et al.

    # 2002 RAS, GJI 148, 356388

    Mesure du dplacement cosismique U

    (Van der Woerd et al., 2002)

    (Peltzer et al., 1999)

    (Peltzer et al., 1999)

  • Pour calculer V, on mesure le dcalage d'objets (moraines, cnes alluviaux, etc) que l'on peut dater (14C, 10Be, 26Al, 37Cl)

    |||

    |

    |

    ||

    |

    ||||

    |||||

    |||

    |||

    ||

    ||

    ||

    ||||

    |||

    |||||||||

    ||||

    |

    ||

    |

    |||

    ||||||||

    |

    ||||

    ||||||||||||||

    |||||||||||

    ||||||||||||

    ||||||||||

    |

    |

    |||||||||||

    |||||||||||||

    ||||||||

    |||||||||||||

    ||||

    |||||

    |||||

    |

    ||||||||||||||||||

    |||||||||||||||||||||

    |||||||||||||

    |

    ||||||||||||

    WG EG

    WV

    CO

    EOWO

    M2

    2 km

    M1 EC

    6311ka

    639 ka

    619 ka

    637 ka 6112 ka

    7715 ka

    7213 ka

    519 ka

    535 ka

    384 ka

    406 ka

    468 ka

    355 ka

    326 ka

    8416 ka

    225 ka

    419 ka

    325 ka

    527 ka

    62 ka

    434 ka

    474 ka

    405 ka

    497 ka

    445ka

    10513 ka

    10711 ka

    536 ka

    536 ka

    8511 ka 122 ka

    303 ka

    223 ka

    355 ka

    144 ka

    173ka

    41 ka

    7010 ka

    416 ka

    738 ka

    428 ka

    (Mriaux et al., 2000)

    26.3 1.4 mm/an

    (Mriaux et al., 2000)

  • At six different sites we dated as many as 93 quartz pebblesand 22 organic samples to constrain the ages of the cumulativeoffsets of 11 distinct morphological markers. The large numberof samples is paramount in obtaining statistically meaningfulcosmogenic ages, and in identifying clearly and discardingoutliers on any given terrace. Several independent values of

    both the marker ages and slip-rates, based either on cosmo-genic or 14C dating, are consistent with one another at each siteand from site-to-site (Fig. 31), giving us confidence in individualrate determinations. Overall, our estimate of the slip-rate isdetermined within an uncertainty of t2.0 mm yrx1, and theaverage value of 11.5 mm yrx1 is robust (Fig. 31).For offset risers, the ages we take, and hence the slip-rates,

    depend on field interpretation regarding the terraces (strathin general, fill in one case), the nature of which may vary fromsite-to-site or at a given site. An end-member scenario, con-sidered highly unlikely, is that the ages of all riser offsets arethose of upper terraces. Slip-rates derived in this scenarioare y7 mm yrx1. In view of geological evidence, we believe7 mm yrx1 to be implausibly small. Nonetheless, this value isgreater than the rate inferred from two epoch remeasurementsof the few extant GPS stations north and south of the KunlunFault (Chen et al. 2000). Until a denser and longer GPS surveyis undertaken, slip-rates based on this technique should beregarded as preliminary.Our average rate value of 11.6t0.8 mm yrx1 in Xidatan

    Dongdatan (Fig. 15), which is based only on cosmogenicdating of offset terrace risers, is consistent with those derivedfrom other geological studies with different dating tech-niques. Zhao et al. (1994) and Zhao (1996), in particular,documented 10 offsets of gullies and terrace risers in Xidatan,ranging from 10 to 152 m, and retrieved seven TL or 14Cages, ranging from 2.14 to 12.0 kyr BP, with uncertainties of69 per cent. From this, they derived a Holocene slip-rateof about 11.5 mm yrx1. Unfortunately, without error estimateson the offsets, the uncertainty on that rate cannot be assessed.The average Quaternary rate estimated by Kidd & Molnar(1988) (1020 mm yrx1), loosely brackets both our values andthose of Zhao et al. In a strict sense, however, it cannot besimply