Professor Ian Shennan
I have a long association with the Department, BSc 1976, PhD 1991, Chair of the Board of Studies 1997-2000. My main areas of research focus on sea-level and environmental changes and I set up the Sea Level Research Unit in 1987, attracting more than 30 research grants and contracts worth more than £2 million.
Current research areas are:
- Late-Quaternary Sea-Level And Environmental Changes In The North Sea Region
- Land Uplift And Subsidence In The United Kingdom And North Sea Region
- Global Meltwater Discharge Since The Last Glacial Maximum
- Earthquake Hazards in Alaska, Washington and Oregon, USA
Land uplift and subsidence In Britain and Ireland
This work started in the 1980s, with first paper, published 1987, quantifying the regional-scale pattern of uplift and subsidence around the North Sea. This was followed, in 1989, Journal of Quaternary Science, by the first analysis for 35 years to provide a quantitative estimate of current land uplift and subsidence in mainland Great Britain to be supported by the geological and oceanographic data. Significant advances in data quality and spatial cover followed over the next 10 years, with a revised analysis (Shennan & Horton, 2002) that included tidal range changes and anthropogenic-induced subsidence. Further consideration of sediment compaction and integration of field data with geophysical models led to the most recent updates, Shennan et al 2006 and 2009. These provide our most reliable measures of the long term rate of relative land/sea-level change in Britain and Ireland, prior to any 20th century increase in sea level. To use this map alongside any predictions of future global sea level rise you must add the prediction (for example, from the latest IPCC report) to the value for a chosen location. If your location includes areas of soft sediments, such as coastal lowlands or reclaimed esturine sites, you must also add the effect of sediment compaction to get the total amount of land subsidence.
The image is available here, the full paper/article is available from GSA Today: http://www.geosociety.org/gsatoday/archive/19/9/article/i1052-5173-19-9-52.htm “Late Holocene relative land- and sea-level changes: Providing information for stakeholders”. Authors: Ian Shennan, Sea Level Research Unit, Department of Geography, Durham University, Durham DH1 3LE, UK; Glenn Milne, Department of Earth Sciences, University of Ottawa, Ottawa, K1N 6N5, Canada and Sarah Bradley, Department of Earth Sciences, Durham University, Durham, DH1 3LE.
Photograph 1: Loch nan Corr, Kintail, Scotland. Taking sediment cores from what is now the freshwater loch to measure land uplift. It was previously a marine embayment, but gradual land uplift has raised it above the level of even the highest tides.
Photograph 2: Ancient forest and peat layers at Druridge Bay - shows how relative sea-level has risen in comparison to the land, even where the land is still rising, its just that sea level has risen even faster as the ice sheets melted.
Late-Quaternary Sea-Level and Environmental Changes in the North Sea Region
This involves application of a wide range of methods of palaeo-environmental reconstruction (field, laboratory, experimental and analytical techniques) and development of a new research methodology.
- First developed during the work on the Fenlands and subsequently applied in many other areas the “sea-level tendency” methodology enables analysis and correlation of diverse evidence of relative sea-level changes and coastal evolution.
- New research in NW Scotland, including development of methods new to the UK, is revising our understanding of sea-level change and crustal deformation at the regional scale. The resulting 16000 year record of relative sea-level change in NW Scotland is one of the longest and most detailed available in the world and is very important in constraining models of earth rheology and glacial history since the Last Glacial Maximum.
- Integrating quantitative models of glacio-hydro-isostatic models with tide models to produce simulations of the Holocene changes in coastlines, bathymetry and tides in the North Sea.
- Modelling of tidal range changes during the Holocene, implications for reconstructing sea-level changes and sediment movement.
Global Meltwater Discharge Since the Last Glacial Maximum
The 16000 year record of relative sea-level change (RSL) in NW Scotland allows calculation of quantitative limits of global meltwater discharge in terms of both timing and magnitude (see recent publications). Various claims in the literature about periods of rapid ice decay and subsequent climate changes can be readily tested by such RSL records. In order to remove any effects of local ice sheet chronology my current research in this area focuses upon establishing a better spatial coverage, to create similarly comprehensive records for 3 areas in Scotland. This will be a powerful discriminator between the different model solutions and hence the timing and source of meltwater discharge.
Earthquake and Tsunami Hazards in Alaska, Washington and, Oregon
This applied aspect of sea-level research utilises theory and methods of analysis developed at Durham to the identification and analysis of great earthquakes in plate-boundary locations, with recent projects focussed upon Washington, Oregon and Alaska.
- Application of microfossil techniques to differentiate between seismic and non-seismic relative land/sea-level movements
- Development and application of quantitative methods to estimate relative land/sea-level changes throughout multiple Holocene earthquake deformation cycles
- Verification of methods against observations from the 1964 Alaska Earthquake (Magnitude 9.2)
- Identification of pre-seismic relative sea-level rise prior to the 1964 Alaska Earthquake and other late Holocene great earthquakes in Alaska
- Ongoing research focuses upon whether pre-seismic relative sea-level rise represents a pre-cursor to great earthquakes
- Variation in the locations and size of earthquake rupture zones, fault segmentation and long-term mountain building
- Evidence for tsunamis associated with great earthquakes
Photograph 1: Sediment section exposed at the top of the present storm beach of ‘The Forgotten Coast’ of Alaska, east of Cape Yakataga. The boulders are those found at the upper limit of the modern beach. Immediately behind the boulders the sea has eroded into sediments, forming a small cliff, and exposing different sediment layers of peat, mud and sand. Ron Bruhn, University of Utah, stands on the top of the section.
Photograph 2: Close up of the sediment section in photograph 1. This part of the section is the horizontal boundary between two layers of sediment, about 1m above the boulders in photograph 1. The scale arrow is 10cm total, the lower part of the arrow shows 1cm increments. The wavy line in the top part of the image is simply where we have cleaned the sediment surface to expose the uncontaminated sediment, free from soil that has fallen down the cliff. The sharp, horizontal boundary, represent a change from beach sand (light brown, coarse texture) to grey mud. Fossils in the mud and radiocarbon dating show it to be sediment laid down in a lagoon or shallow lake approximately 1500 years ago. So, the scientific interpretation is that an earthquake caused uplift of at least 2m, instantaneously raising a beach environment to above high tide level, allowing a freshwater lagoon or shallow lake to develop.
Photograph 3: A view of Mt. St Elias and Icy Bay. The area encompasses part of the Wrangell - Saint Elias National Park and Mt. Saint Elias rises from tidewater to an elevation in excess of 5400m and the region is marked by North America's greatest alpine and piedmont glaciers. This spectacular region is an enigma in the study of plate tectonics and great earthquakes because of structural complexity in the transition from strike-slip to subduction plate boundaries, and its remoteness.
Photograph 4: Aerial view from the helicopter of the Forgotten Coast, Alaska, showing linear patterns caused by different tree growth, grasses and swamp vegetation communities. These vegetation differences reflect the underlying soil, trees growing on the more sandy ridges. The ridges and hollows reflect old beach ridges and sand dune, uplifted above sea level during great earthquakes.
- Khan, Nicole S., Horton, Benjamin P., Engelhart, Simon, Rovere, Alessio, Vacchi, Matteo, Ashe, Erica L., Törnqvist, Torbjörn E., Dutton, Andrea, Hijma, Marc P. & Shennan, Ian Inception of a global atlas of sea levels since the Last Glacial Maximum. Quaternary Science Reviews. 2019;220:359-371.
- Horton, B.P., Shennan, I., Bradley, S., Cahill, N., Kirwan, M., Kopp, R.E. & Shaw, T.A. Predicting marsh vulnerability to sea-level rise using Holocene relative sea-level data. Nature Communications. 2018;9:2687.
- Shennan, I., Bradley, S.L. & Edwards, R. Relative sea‐level changes and crustal movements in Britain and Ireland since the Last Glacial Maximum. Quaternary Science Reviews. 2018;188:143-159.
- Shennan, I., Garrett, E. & Barlow, N.L.M. Detection limits of tidal-wetland sequences to identify variable rupture modes of megathrust earthquakes. Quaternary Science Reviews. 2016;150:1-30.
- Liu, J., Milne, G.A., Kopp, R.E., Clark, P.U. & Shennan, I. Sea-level constraints on the amplitude and source distribution of Meltwater Pulse 1A. Nature Geoscience. 2016;9:130-134.
- Garrett, E., Barlow, N.L.M., Cool, H., Kaufman, D., Shennan, I. & Zander, P. Constraints on regional drivers of relative sea-level change around Cordova, Alaska. Quaternary science reviews. 2015;113:48-59.
- Brew, David S., Horton, Benjamin P., Evans, G., Innes, James B. & Shennan, Ian Holocene sea-level history and coastal evolution of the north-western Fenland, eastern England. Proceedings of the Geologists' Association. 2015;126:72-85.
- Garrett, E., Shennan, I., Woodroffe, S.A., Cisternas, M., Hocking, E.P. & Gulliver, P. Reconstructing paleoseismic deformation, 2: 1000 years of great earthquakes at Chucalén, south central Chile. Quaternary Science Reviews. 2015;113:112-122.
- Shennan, I., Barlow, N.L.M., Carver, G.A., Davies, F.P., Garrett, E. & Hocking, E.P. Great tsunamigenic earthquakes during the last 1000 years on the Alaska megathrust. Geology. 2014;42:687-690.
- Shennan, I., Bruhn, R., Barlow, N.L.M., Good, K. & Hocking, E.P. Late Holocene great earthquakes in the eastern part of the Aleutian megathrust. Quaternary Science Reviews. 2014;84:86-97.
- Shennan, I., Barlow, N.L.M., Combellick, R., Pierre, K. & Stuart-Taylor, O. Late Holocene paleoseismology of a site in the region of maximum submergence during the 1964 Mw 9.2 Alaska earthquake. Journal of Quaternary Science. 2014;29:343-350.
- Barlow, N.L.M., Shennan, I., Long, A.J., Gehrels, W.R., Saher, M.H, Woodroffe, S.A. & Hillier, C. Salt marshes as late Holocene tide gauges. Global and Planetary Change. 2013;106:90-110.
- Watcham, E.P., Shennan, I. & Barlow, N.L.M. Scale considerations in using diatoms as indicators of sea-level change: lessons from Alaska. Journal of Quaternary Science. 2013;28:165-179.
- Kuchar, J., Milne, G., Hubbard, A., Patton, H., Bradley, S., Shennan, I. & Edwards, R. Evaluation of a numerical model of the British–Irish ice sheet using relative sea-level data: implications for the interpretation of trimline observations. Journal of Quaternary Science. 2012;27:597-605.
- Shennan, I., Milne, G. & Bradley, S. Late Holocene vertical land motion and relative sea-level changes: lessons from the British Isles. Journal of Quaternary Science. 2012;27:64-70.
- Shennan, I. Relative land/sea level change is not the same as vertical land motion: Comment on Rennie, A.F. and Hansom, J.D. (2011) "Sea level trend reversal: land uplift outpaced by sea level rise on Scotland's coast" Geomorphology 125: 193-202. Geomorphology. 2012.
- Barlow, N.L.M., Shennan, I. & Long, A.J. Relative sea-level response to Little Ice Age ice mass change in south central Alaska: Reconciling model predictions and geological evidence. Earth and Planetary Science Letters. 2012;315-316:62-75.
- Bradley, S.L., Milne, G.A., Shennan, I. & Edwards, R. An improved Glacial Isostatic Adjustment model for the British Isles. Journal of Quaternary Science. 2011;26:541-552.
- Shennan, I. Palaeoclimate: Sea level from global to local. Nature Geoscience. 2011;4:283.
- Horton, B.P. & Shennan, I. Compaction of Holocene strata and the implications for relative sea-level change on the east coast of England. Geology. 2009;37:1083-1086.
- Teferle, F.N., Bingley, R.M., Orliac, E.J., Williams, S.D.P., Woodworth, P.L., McLaughlin, D., Baker, T.F., Shennan, I., Milne, G.A., Bradley, S.L. & Hansen, D.N. Crustal motions in Great Britain: evidence from continuous GPS, absolute gravity and Holocene sea level data. Geophysical Journal International. 2009;178:23-46.
- Shennan, I., Milne, G. & Bradley, S.L. Late Holocene relative land - and sea-level changes: providing information for stakeholders. GSA Today. 2009;19:52-53.
- Shennan, I. Late Quaternary sea-level changes and palaeoseismology of the Bering Glacier region, Alaska. Quaternary Science Reviews. 2009;28:1762-1773.
- Shennan, I., Bruhn, R. & Plafker, G. Multi-segment earthquakes and tsunami potential of the Aleutian megathrust. Quaternary Science Reviews. 2009;28:7-13.
- Woodworth, P.L., Teferle, F.N., Bingley, R.M., Shennan, I. & Williams, S.D.P. Trends in UK mean sea level revisited. Geophysical Journal International. 2009;176:19-30.
- Shennan, I., Brooks, A.J., Bradley, S.L., Edwards, R.J., Milne, G.A. & Horton, B. Postglacial relative sea-level observations from Ireland and their role in glacial rebound modelling. Journal of Quaternary Science. 2008;23:175-192.
- Edwards, R., Brooks, A., Shennan, I., Milne, G. & Bradley, S. Reply: Postglacial relative sea-level observations from Ireland and their role in glacial rebound modelling. Journal of Quaternary Science. 2008;23:821-825.
- Milne, G.A., Shennan, I., Youngs, B.A.R., Waugh, A.I., Teferle, F.N., Bingley, R.M., Bassett, S.E., Cuthbert-Brown, C. & Bradley, S.L. Modelling the glacial isostatic adjustment of the UK region. Philosophical Transactions of the Royal Society. 2006;364:931-948.
- Shennan, I., Bradley, S., Milne, G., Brooks, A., Bassett, S. & Hamilton, S. Relative sea-level changes, glacial isostatic modelling and ice-sheet reconstructions from the British Isles since the Last Glacial Maximum. Journal of Quaternary Science. 2006;21:585-599.
- Shennan, I., Hamilton, S., Hillier, C., Hunter, A., Woodall, R., Bradley, S., Milne, G., Brooks, A. & Bassett, S. Relative sea-level observations in western Scotland since the Last Glacial Maximum for testing models of glacial isostatic land movements and ice-sheet reconstructions. Journal of Quaternary Science. 2006;21:601-613.
- Shennan, I., Hamilton, S. L., Hillier, C. & Woodroffe, S. A 16 000-year record of near-field relative sea-level changes, northwest Scotland, United Kingdom. Quaternary International. 2005;133-134:95-106.
- Hamilton, S. & Shennan, I. Evidence for two great earthquakes at Anchorage, Alaska and implications for multiple great earthquakes through the Holocene. Quaternary Science Reviews. 2005;24:2050-2068.
- S.L. Hamilton & I. Shennan Late Holocene great earthquakes and relative sea-level change at Kenai, southern Alaska. Journal of Quarternary Science. 2005;20:95-111.
- Hamilton, S. & Shennan, I. Late Holocene relative sea-level changes and the earthquake deformation cycle around upper Cook Inlet, Alaska. Quaternary Science Reviews. 2005;24:1479-1498.
- Shennan, I. Peat. Encyclopedia of Coastal Science. 2005;762-764.
- Mastronuzzi, G., Sanso, P. & Shennan, I. Quaternary coastal morphology and sea-level changes - an introduction. Quaternary Science Reviews. 2005;24:1963-1968.
- Horton, B. P., Innes, J. B., Shennan, I., Lloyd, J. M. & McArthur, J. J. Holocene coastal change in east Norfolk, UK: palaeoenvironmental data from Somerton and Winteron Holmes, near Horsey. Proceedings of the Geologists' Association. 2004;115:209-220.
- I. Shennan, T. Coulthard, R. Flather, B. Horton, M. Macklin, J. Rees & M. Wright Integration of shelf evolution and river basin models to simulate Holocene sediment dynamics of the Humber Estuary during periods of sea-level change and variations in catchment sediment supply. Science of the Total Environment. 2003;314-316:737-754.
- Zong, Y., Shennan, I., Combellick, R.A., Hamilton, S.L. & Rutherford, M.M. Microfossil evidence for land movements associated with the AD 1964 Alaska earthquake. The Holocene. 2003;13:7-20.
- I. Shennan & G. Milne Sea-level observations around the Last Glacial Maximum from the Bonaparte Gulf, NW Australia. Quaternary Science Reviews. 2003;22:1543-1547.
- Shennan, I., Peltier, W.R., Drummond, R. & Horton, B.P. Global to local scale parameters determining relative sea-level changes and the post-glacial isostatic adjustment of Great Britain. Quaternary Science Reviews. 2002;21:397-408.
- Shennan, I. & Horton, B. Holocene land- and sea-level changes in Great Britain. Journal of Quaternary Science. 2002;17:511-526.
- W.R. Peltier, I. Shennan, R. Drummond & B. Horton On the postglacial isostatic adjustment of the British Isles and the shallow viscoelastic structure of the Earth. Geophysical Journal International. 2002;148:443-475.
- I. Shennan & B.P. Horton Relative sea-level changes and crustal movements of the UK. Journal of Quaternary Science. 2002;16:511-526.
- Shennan, I., Lambeck, K., Horton, B. P., Innes, J. B., Lloyd, J. M., McArthur, J. J., Purcell, A. & Rutherford, M. M. Late Devensian and Holocene records of relative sea-level changes in northwest Scotland and their implications for glacio-hydro-isostatic modelling. Quaternary Science Reviews. 2000;19:1103-1136.
- I. Shennan, B. Horton, J.B. Innes, R. Gehrels, J.M. Lloyd, J.J. McArthur & M.M. Rutherford Late Quaternary sea-level changes, crustal movements and coastal evolution in Northumberland, UK. Journal of Quaternary Science. 2000;15:215-237.
- Lloyd, J. M., Shennan, I., Green, F., Kirby, J. & Rutherford, M. Holocene relative sea-level changes in the inner Solway Firth. Quaternary International. 1999;60:83 - 105.
- Shennan, I., Scott, D., Rutherford, M.M. & Zong, Y. Microfossil analysis of sediments representing the 1964 earthquake, exposed at Girdwood Flats, Alaska. Quaternary International. 1999;60:55-73.
- I. Shennan, M. Tooley, F. Green, J.B. Innes, K. Kennington, J.M. Lloyd & M.M. Rutherford Sea level, climate change and coastal evolution in Morar, northwest Scotland. Geologie en Mijnbouw. 1999;77:274-262.
- Shennan, I., Long, A.J. & Metcalfe, S. Editorial: IGCP Project 367 'Late Quaternary records of rapid coastal change: application to present and future conditions' and twenty-five years of progress in research. Holocene. 1998;8:125-128.
- Shennan, I., Long, A.J. & Metcalfe, S. Late Quaternary records of rapid coastal change: application to present and future conditions' and twenty-five years of progress in research. Holocene. 1998;8:125-128.
- Long, A.J. & Shennan, I. Models of rapid relative sea-level change in Washington and Oregon, USA. Holocene. 1998;8:129-142.
- Shennan, I., Long, A.J. & Metcalfe, S. Sea-level changes: IGCP Project 367. Special issue of The Holocene. 1998;8:125-247.
- Shennan, I., Long, A.J., Rutherford, M.M., Kirby, J.R., Green, F.M.L., Innes, J.B. & Walker, K. Tidal marsh stratigraphy, sea-level change and large earthquakes, II: Events during the last 3500 years at Netarts Bay, Oregon, USA. Quaternary Science Reviews. 1998;17:365-393.
- Nelson, A., Shennan, I. & Long, A.J. Identifying coseismic sea-level change in tidal wetland stratigraphic sequences in the Cascadia subduction zone of western North America. Journal of Geophysical Research. 1996;101:6115-6135.
- Shennan, I., Long, A.J., Rutherford, M.M., Green, F.M., Innes, J.B., Lloyd, J.M., Zong, Y. & Walker, K. Tidal marsh stratigraphy, sea-level change and large earthquakes, 1; a 5000 year record in Washington, U.S.A. Quaternary Science Reviews. 1996;15:1-37.
- Shennan, I., Innes, J.B., Long, A.J. & Zong, Y. Holocene relative sea-level changes at Kentra Moss, Argyll, Northwestern Scotland. Marine Geology. 1995;124:43-59.
- Shennan, I., Innes, J.B., Long, A.J. & Zong, Y. Late Devensian and Holocene relative sea-level changes in northwestern Scotland: New data to test existing models. Quaternary International. 1995;26.
- Shennan, I., Innes, J.B., Long, A.J. & Zong, Y. Late Devensian and Holocene relative sea-level changes at Loch nan Eala, near Arisaig, Northwest Scotland. Journal of Quaternary Science. 1994;9:261-283.
- Long, A.J. & Shennan, I. Sea-level changes in Washington and Oregon and the 'Earthquake deformation cycle'. Journal of Coastal Research. 1994;10:825-838.
- Long, A.J. & Shennan, I. Holocene sea-level and crustal movements in southeast and northeast England, UK. Quaternary Proceedings. 1993;3:15-19.
- Shennan, I., Innes, J.B., Long, A.J. & Zong, Y. Late and post glacial sea-level movements in northwest Scotland, UK. Norsk Geologisk Tidsskrift. 1993;73:161-174.
- Shennan, I., Innes, J.B., Long, A.J. & Zong, Y. Late-Glacial and Holocene sea-level changes at Rumach, northwest Scotland. Norsk Geologisk Tidsskrift. 1993;73:161-174.
- Shennan, I., Long, A.J. & Horton, B.P. Handbook of Sea-Level Research. Wiley / AGU; 2015.
Chapter in book
- Shennan, Ian Sea level studies: Overview. In: Reference Module in Earth Systems and Environmental Sciences. Elsevier; 2018.
- Shennan, I. Handbook of sea-level research: framing research questions. In: Shennan, I., Long, A.J. & Horton, B.P. Handbook of Sea-Level Research. Hoboken, NJ: John Wiley; 2015:3-25.
- Shennan, I. & Hamilton, S.L. Holocene sea-level changes and earthquakes around Bering Glacier. In: Bering Glacier: Interdisciplinary studies of Earth’s largest temperate surging glacier. Geological Society of America; 2009.
- Shennan, I., Barlow, N. & Combellick, R. Palaeoseismological records of multiple great earthquakes in south-central Alaska - a 4000 year record at Girdwood. In: Active tectonics and seismic potential of Alaska. American Geophysical Union; 2008:185-199.
- Shennan, I., Barlow, N.L.M. & Combellick, R. Palaeoseismological records of multiple great earthquakes in south-central Alaska: a 4000 year record at Girdwood. In: Freymueller, J.T. Haeussler, P.J. Wesson, R.L. & Ekstrom, G. Active tectonics and seismic potential of Alaska. Washington, DC: AGU Geophysical Monograph Series; 2008:185-199.
- Shennan, I. Encyclopedia of Quaternary Science. In: Elsevier; 2007:2967-2974.
- I. Shennan & S. Woodroffe Holocene sea level changes around Loch Duich and Loch Alsh, Northwest Highlands. In: R.M. Tipping The Quaternary of Glen Affric and Kintail. Quaternary Research Association; 2003:123-124.
- S.L. Hamilton & I. Shennan Pre-seismic land and sea-level movements and great Holocene earthquakes, Alaska. In: Coastal Environmental Change During Sea Level Highstands: A Global Synthesis with Implications for Management of Further Coastal Change. IGCP Project 437 International Meeting; 2002:38.
- Shennan, I., Lambeck, K., Flather, R., Wingfield, R., Horton, B.P., McArthur, J.J., Innes, J.B., Lloyd, J.M. & Rutherford, M.M. Modelling western North Sea palaeogeographies and tidal changes during the Holocene. In: Shennan, I. & Andrews, J.E. Holocene land ocean interactions and environmental change around the North Sea. London: The Geological Society; 2000:299-319.
- Long, A.J., Innes, J.B., Shennan, I. & Tooley, M.J. Coastal stratigraphy: a case study from Johns River, Washington. In: Jones, A.P., Tucker, M.E. & Hart, J.K. The description and analysis of Quaternary stratigraphic field sections. Quaternary Research Association Technical Guide 7, Quarternary Research Association; 1999:267-286.
Other (Digital/Visual Media)
- Horton, B. P., Edwards, R. J. & Lloyd, J. M. Implications of a microfossil based transfer function in Holocene sea-level studies. 2000;Special No. 166:41 - 54.
- Shennan, I., Long, A.J. & Barlow, N. Recurrent Holocene paleoseismicity and associated land/sea-Level changes in south central Alaska. 2007;38.
- Shennan, I., Hamilton, S.L. & Long, A.J. Late Holocene paleoseismicity and associated land/sea level change in the greater Anchorage area. 2004;55.
- Shennan, I. & Hamilton, S.L. Late Holocene paleoseismicity and associated land/sea level change in the greater Anchorage area. 2003;86.
Department of Geography
Department of Geography
- Land and Sea-Level Changes Around Britain
- Recurrent Holocene Paleoseismicity and Associated Land / Sea Level Changes in the Greater Anchorage Area