SZO Seminar Notes – April 1, 2015:  Short- and long-term coupling and strain release: approaches to constraining coastal vertical and horizontal displacement fields

The basic message conveyed in this discussion is that simple tools can provide important constraints.  The paper discussed provided an example of the type tool envisioned; e.g., standardized well-planned marine intertidal surveys.  More specifically, the 'hair-brained scheme' proposed was to develop a SZO 'Multi-laboratory' that would include

1. A series of coordinated surveys done by local persons.
2. Surveys re-surveyed regularly.
3. These 'citizen' measurements would be combine with those made more sophisticated techniques.
4. Fundamental observations might include biological markers and tidal levels, geomorphic landmarks, tsunami deposits, biostratigraphy of sedimentary stratigraphy, sessile intertidal organisms.

The paper by Melnick et al. (2012) provides an example of how to measure post-earthquake vertical deformations using biological markers and relative sea level.  Sessile (attached) organisms span different elevations with respect to the tides, with limits that depend on environmental and ecological conditions.  The interplay between the tidal range and the biological zonation range is key (to be able to resolve deformation).   Melnick et al. (2012) describes a survey and analysis of stranded mussel bands along the Chilean coast after the 2010 earthquake.  Much of analysis in this study was required in order to estimate the pre-earthquake mean tidal level (importance of having pre-event benchmark data).  The authors compared their mussel measurements to others made using GPS, tide gage data, coralline algae, and LiDar.  Calibration with other methods allowed them to identify potential biases in the mussel measurements and correct for them.  Their mussel measurements made a significant difference in the slip model.

Interestingly, the approach of using biological markers to measure earthquake-generated uplift and subsidence in Chile dates back to before Charles Darwin, to Maria Graham in 1822.  Darwin's observations may be found at http://www.geo.cornell.edu/geology/faculty/RWA/research/current_research/chile-m-88-earthquake-page/darwins-description-of-the-.html) and Graham's rebuttal to those who refuted her observations at https://books.google.com/books?id=eRxFAQAAMAAJ&pg=PA246&lpg=PA246&dq=callcott+greenough&source=bl&ots=DgW3YDRW1Y&sig=9Z-V_XInQFRzirLbBQfkOi0iAMk&hl=en&sa=X&ei=TG4dVaWXJJCvoQT2t4HYAw&ved=0CDQQ6AEwBA#v=onepage&q=callcott%20greenough&f=false.  The use of mussels also was significant in Plafker’s study and book about the 1964 Alaska earthquake.

A benefit of biological measures is that they may also be used to assess paleo-deformation, and possibly to identify forewarnings of impending earthquakes. 

Targets: seasonal variations, global sea level change, along-shore variations, comparison between different environmental settings.

Subduction processes: interseismic assessments, paleo and post-earthquake constraints

This 'multi-laboratory' has strong links with coastal marine biology and climate change studies.  Data collected could have broader impacts: e.g., for understanding global sea level rise, and the ecological/biological response to secular and sudden changes (earthquakes and non-tectonic changes).  It also provides an avenue for citizen science (e.g. Beach watchers).  Key elements include

• People in difference countries.  
• Building of a database for organizing efforts and archiving/accessing data.
• An advisory committee to coordinate.
• Small grants to cover sampling etc..
• Annual meetings to assess progress and performance.