docDeterminación de la frecuencia de los deslizamientos
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Determinación de la frecuencia de los deslizamientos
ASSESSING FREQUENCY OF LANDSLIDES Determinación de la frecuencia de los deslizamientos Primeras roturas y episodios de reactivación ASSESSING FREQUENCY OF LANDSLIDES Aproximanciones para evaluar la probabilidad de ocurrenca de los deslizamientos Método Heurístico (criterio experto) z Correlación con los desencadenantes z Análisis probabilístico z Realciones Magnitud – frecuencia z Curvas de fluencia z Modelación numérica z Picarelli et al. 2005. Hazard characterization and quantification. In O. Hungr, R. Fell, R. Couture and E. Eberthardt (editors) Landslide Risk Management. Taylor and Francis, London. pp. 27-61 ASSESSING FREQUENCY OF LANDSLIDES Aproximación heurística z Primeros intentos de cartografía de peligrosidad (Plan ZERMOS) ASSESSING FREQUENCY OF LANDSLIDES Aproximación heurística 60 z Identificación de umbrales (i.e. lluvia crítica) Caine: I = 14.82 D-0.39 donde I, en mm/h D, en hr Caine 1980 Cancelli & Nova 1985 Rainfall Intensity (mm/h) ASSESSING FREQUENCY OF LANDSLIDES Correlación con desencadenantes Wieckzorek 1987 40 Larsen & Simon 1993 20 0 0 12 24 Duration (hours) 36 48 ASSESSING FREQUENCY OF LANDSLIDES Correlación con desencadenantes Suposiciones: La frecuencia de los deslizamientos es la del mecanismo desencadenante Restricciones desventajas: Puede haber diferentes desencadenantes en la región (lluvia, fusión de nieve, terremotos, socavación fluvial, etc) Eventos desencadenantes de la misma intensidad pueden terner distintas consecuencias en las laderas (agotamiento de derrubios disponibles en eventos muy próximos, etc) ASSESSING FREQUENCY OF LANDSLIDES Correlación con desencadenantes: umbrales críticos Casos históricos. Serra de la Fembra Morta, Pirineo Oriental. 1940 Correlación con desencadenantes: umbrales críticos ASSESSING FREQUENCY OF LANDSLIDES 6 - 7 / nov / 1982 Tres tormentas de gran intensidad que provocaron numerosos deslizamientos superficiales 8 / se p / 1 9 9 2 Cuenca alta del río Llobregat, Pirineo Oriental Upper 17 - 18 / dec / 1997 190 mm en 24/36 hr 1982 Cercs 1992 Port del Comte 200 Daily rainfall (mm) Daily rainfall (mm) ASSESSING FREQUENCY OF LANDSLIDES Correlación con desencadenantes: umbrales críticos 100 0 200 100 0 26-Sep 10-Oct 24-Oct 7-Nov 21-Nov 28-Jul 11-Aug 25-Aug 8-Sep 22-Sep ASSESSING FREQUENCY OF LANDSLIDES Correlación con desencadenantes: umbrales críticos Cal Borni, Vallcebre, Pirineo Oriental. Noviembre 1982 ASSESSING FREQUENCY OF LANDSLIDES Correlación con desencadenantes: umbrales críticos Comprobando el umbral. Berga, Pirineo Oriental. Diciembre 1997 ASSESSING FREQUENCY OF LANDSLIDES Periodo de retorno en la estación de Cercs ASSESSING FREQUENCY OF LANDSLIDES Normalizando umbrales RDN rainy-day normal Wilson, R.C. 1997. “Normalizing rainfall/debris flow thresholds along the U.S. Pacific Coast for long-term variations in precipitation climate”. In C-I Chen (ed.) Debris-flow hazards mitigation: mechanics, prediction, and assessment. ASCE. pp. 32-43 ASSESSING FREQUENCY OF LANDSLIDES Probability analysis: annual probability of occurrence ni P= N ni number of landslides of magnitude M occurred within a span of time. N the total number of landslides The annual exceedance probability (PE) is 1 PE = TR TR return period of the event ( average # of years between two events equally or exceeding magnitude M). ASSESSING FREQUENCY OF LANDSLIDES Probability of exceedance Poisson probability models P [ N (t ) ≥ 1] = 1 − e − t µ N(t) number of landslide (or landslide clusters) expected to occur during a especified time interval (t) µ future mean recurrence interval Crovelli, R.A. 2000. Probabilistic models for estimation of number and cost of landlsides. U.S. Geological Survey Open File Report 00-249, 23 pp. http://pubs.usgs.gov/of/2000/ofr-00-0249/ProbModels.html ASSESSING FREQUENCY OF LANDSLIDES Magnitude – frequency relationships Approach taken from seismology Gutenberg- Richter power law: log N ( m ) = a − bM N number of events equal of greater than M M magnitude a and b , constants ASSESSING FREQUENCY OF LANDSLIDES Magnitude – frequency relationships For landslides (Hovius et al. 1997; Pelletier et al. 1997) found: N E = CAL− β NE number of events equal of greater than A A magnitude (area) C and β , constants Pelletier et al. 1997 ASSESSING FREQUENCY OF LANDSLIDES Magnitude – frequency relationships The linear segment of these log-log relationships have been suggested for assessing (extrapolating) frequency of Both mid-size and large Landslides (Malamud et al. 2004; Picarelli et al. 2005) Malamud, B.D.; Turcotte, D.L.; Guzzetti, F. And Reichenbach, P. 2004. Landslide inventories and their statistical properties. Earth Surface Processes and Landforms, 29: 687-711 Malamud et al. 2004 ASSESSING FREQUENCY OF LANDSLIDES Where the data for M-f analyses come from? Direct information sources (landslide data bases) - landslide incident records - monitoring networks - historical archives - remote sensing techniques ASSESSING FREQUENCY OF LANDSLIDES Where the data for M-f analyses come from? ASSESSING FREQUENCY OF LANDSLIDES Reconstructing landslide series Why are they needed? z z z Some historical records are not complete or they are too short Validity of the extrapolation of M-f relations for large landslides has not been checked yet M-f relationships are not conceived for assessing landslide reactivation events ! ASSESSING FREQUENCY OF LANDSLIDES Reconstructing landslide series Available dating methods for reconstructing landslide series and their reactivation events z z z z Incremental dating Radiometric methods Age equivalence methods. Calibrated ages Relative chronologies ASSESSING FREQUENCY OF LANDSLIDES Reconstructing landslide series (1) Relative chronology may become numerical when calibrated ASSESSING FREQUENCY OF LANDSLIDES Incremental dating: Dendromorphology ASSESSING FREQUENCY OF LANDSLIDES Incremental dating: Dendromorphology Sta. Coloma. Andorra Bc. Boés. Llavorsí ASSESSING FREQUENCY OF LANDSLIDES Incremental dating: Dendromorphology Osterkamp & Hupp. 1987. Reviews of Eng. Geology 7, pp. 157-163 GSA ASSESSING FREQUENCY OF LANDSLIDES Incremental dating: Dendromorphology From concentric to eccentric growth Reaction wood (darker colour) 1987 Reaction wood ASSESSING FREQUENCY OF LANDSLIDES Detecting reactivation events (earthflows) Llavorsí earthflow, Central Pyrenees ASSESSING FREQUENCY OF LANDSLIDES Reconstructing landslide reactivation events Interpreting dating results ASSESSING FREQUENCY OF LANDSLIDES Event age Minimum age Event and/or Maximum age Event age Lang et al. 1999, Geomorphology, 30: 33-52 Event and/or minimum age ASSESSING FREQUENCY OF LANDSLIDES Obtaining landslide sequences La Coma. Buried soil Pedra. Buried tree stem C-14 dating ASSESSING FREQUENCY OF LANDSLIDES Obtaining landslide sequences: successive events Pedra, Eastern Pyrenees Moya et al. 1997, Paleoclimate Research 19:55-73 ASSESSING FREQUENCY OF LANDSLIDES Obtaining landslide sequences: successive events Pottery fragment found at layer 2 belong to the Bronze Age (consistent with C-14 dating of charcoal) Return period of debris flows events: 730 yr (5 layers) to 610 yr (6 layers) These are maximum TR values. Some events might have been eroded Pedra, Eastern Pyrenees Moya et al. 1997, Paleoclimate Research 19:55-73 ASSESSING FREQUENCY OF LANDSLIDES Obtaining landslide sequences from associated deposits Sequences of earthflow events deduced from associated lacustrine deposits (valley damming) La Barraca, Eastern Pyrennes ASSESSING FREQUENCY OF LANDSLIDES Obtaining landslide sequences from associated deposits Moya et al. 1997, Paleoclimate Research 19:55-73 ASSESSING FREQUENCY OF LANDSLIDES Obtaining landslide sequences from associated deposits ASSESSING FREQUENCY OF LANDSLIDES Obtaining landslide sequences from associated deposits Obtaining landslide sequences from associated deposits ASSESSING FREQUENCY OF LANDSLIDES At least, three damming events since AD 200 AD 350-375 AD 214 and 233 Moya et al. 1997, Paleoclimate Research 19:55-73 ASSESSING FREQUENCY OF LANDSLIDES Obtaining landslide sequences from associated deposits ASSESSING FREQUENCY OF LANDSLIDES Identifying rock avalanches triggered by seismic events Rock avalanches dams. South Puget Sound. WA Identifying rock avalanches triggered by seismic events ASSESSING FREQUENCY OF LANDSLIDES Dead trees (snags) Spider Lake, WA Assumptions: z z Rings predat the avalanche by no more than 100 yr Tree died after a year of being drawned 4 of 6 dated rock avalanche events gave an age of 1200 yr B.P. (about 700 to 1000 A.D.) Schuster, R.L.; Logan, R.L. & Pringle, P.T. 1992. Prehistoric rock avalanches in the Olympic Mountains, Washington. Science, 258: 1620-1621 Lichenometry ASSESSING FREQUENCY OF LANDSLIDES Non-lineal growth Master curves are needed Dating range: hundreds of years (up to few thousand) Sensitive to environmental changes ASSESSING FREQUENCY OF LANDSLIDES Identifying a set of seismically triggered rock avalanches Bull & Brandon. 1998. GSA Bull. 110: 60-84 ASSESSING FREQUENCY OF LANDSLIDES Identifying a set of seismically triggered rock avalanches Bull & Brandon. 1998. GSA Bull. 110: 60-84 ASSESSING FREQUENCY OF LANDSLIDES Identifying a set of seismically triggered rock avalanches ASSESSING FREQUENCY OF LANDSLIDES Relative chronology: landslide sequences Wieczorek, 1987 ASSESSING FREQUENCY OF LANDSLIDES Relative chronology: landslide sequences Lomoschitz et al. 2002, Geomorphology 42, 117-130 ASSESSING FREQUENCY OF LANDSLIDES Relative chronology: landslide sequences Barranco de Tirajana, Canary Islands Lomoschitz et al. 2002, Geomorphology 42, 117-130 ASSESSING FREQUENCY OF LANDSLIDES Relative chronology: landslide sequences Las Filipinas abannoded slide. Barranco de Tirajana, Canary Islands ASSESSING FREQUENCY OF LANDSLIDES Relative chronology: landslide sequences Agualatente large slide. Barranco de Tirajana, Canary Islands ASSESSING FREQUENCY OF LANDSLIDES Relative chronology: landslide sequences Associated lacustrine deposits next Agualatente landslide. Barranco de Tirajana, Canary Islands ASSESSING FREQUENCY OF LANDSLIDES Relative chronology: landslide sequences Different landslide generations associated to Pajonales landslide. Barranco de Tirajana, Canary Islands
