Monitoring Seismic Chatter

Nature News has a good article by Naomi Lubick on recent efforts to set up seismic arrays in Japan and northwestern U.S along the Cascadia subduction zone around the Olympic Peninsula Seattle area to monitor swarms of tiny earthquakes or tremors.

So far these swarms have not been connected to larger earthquakes and cannot be called precursors.. but that's what seismologists are hoping.. that ultimately we may be able to use the pattern of tremors to understand changes in stresses along major faults, giving us a better handle on the timing and location of bigger quakes.

The swarms in Japan seem to be spatially restricted along bands and one speculation is that the subduction of chains of seamounts may be triggering these swarms.

The earthquake swarms along the Cascadia subduction zone in the Olympic Penninsula seem to follow a time line..appearing every 12-14 months.

This regularity is an angle I am sure astrologers are going to be having a field day with ..keep a lookout for claims that these tremor swarms follow planetary cycles (possible for tiny disturbances?) and that you can "predict" big earthquakes by the pattern of these tiny ones.

Sedimentary Basins Meme

Post a satellite image of your favorite exposed ancient sedimentary basin.

Criteria: Do you have a good example of an ancient basin exhumed and exposed which still retains its original geometry, with its basins margins and paleo-shorelines easily identifiable?

Here is mine. The mid-late Proterozoic Cuddapah Basin of south east India. White arrows mark the eastern margin of the basin.

Where there are sediments there must have been a basin. Over time though the original shape of the depression may get obscured mainly through deformation and formation of sucessor basins which may have a different orientation and shape.

The Cuddapah basin however was an intra-cratonic basin i.e a basin which formed far away from plate margins within thick continental crust. Later what was to become India was situated in the interior of Gondwanaland and this region did not experience any Paleozoic sedimentation. And much later Mesozoic rifting was far away from this region further preserving the mid-late Proterozoic basin shape.

The eastern margin did see deformation in the late Proterozoic. The relatively undeformed western margin is still one of my favorite places to visit with exposures of the prominent unconformity between the Archean granites and metsediments and mid Proterozoic basin margin conglomerates and coarse sands representing the earliest deposits.

Here is a figure which shows the location of the Cuddapah basin along with other sedimentary basins of India.

 Source: Geotimes

Leave a link in the comments section so I can keep updating this post with links to your examples.

A New Book On The Geological Evolution Of India

In the latest issue of Current Science, C.P. Rajendran reviews a new book by K. S. Valdiya on the geological evolution of India titled: The Making of India: Geodynamic Evolution.

Prof. K.S. Valdiya has reached a stage in his career where the term "Grand Old Man of Indian Geology" is an entirely appropriate title for him. His deep expertise lies in the geology of the Himalayan mountain chain, but this book is a broader synthesis from Archean times to recent.

I have to admit I found earlier books which synthesized Indian geology in one volume quite disappointing and the review mentions a couple of them. They rambled on and on about formation names and local lithology types and fossils. Written in the days before plate tectonics and geophysical data about the Indian subsurface, the approach was descriptive or one that relied on concepts and terminology that was no longer part of current thinking.

Plate tectonics started appearing in geology textbooks by the early mid 1970's. I graduated in the late 1980's. That there was no textbook which discussed Indian geology within the framework of global plate tectonics more than a decade on is a telling reminder of how slow educational content has been in catching up with the latest developments in the field. Going by C.P. Rajendran's review there was still until 2010 no textbook incorporating all this essential content!

Forty years on, looks like this book will remove that lacuna.

Price is Rs 242/- ( ~$ 5/-) for a 816 page book, courtesy a generous subsidy from the Indian government. It is not yet listed on Amazon and likewise other online sellers. You might have to order it from the publishers Macmillan Publishers India Ltd.

Geological Map Resources Of Afghanistan

The trillions in mineral wealth made me surf a little for good resources on Afghanistan geology.

Here are links to some:

The United States Geological Survey has a Afghanistan Projects website with links to geological map quads ( 1:250,000), Landsat images, reports and photo gallery.

The British Geological Survey has a collection of downloadable maps on geology, mineral distribution, tectonics and hydrogeology.

For an interactive experience the OneGeology portal has a map viewer to browse Afghanistan geology. The portal is administered by the British and French Geological Survey.

Nature News has quite a good article on the recent history of geological mapping of Afghanistan and tensions and political conflicts over control of this mineral wealth.

GeoCommunity.. a geospatial news and education resource site has a collection of links to maps, images and viewer applications.

Matt Ridley On Ocean Acidification and Coral Calcification

Matt Ridley (author of Genome and the Red Queen) on his blog The Rational Optimist clarifies recent thinking about ocean acidification and its predicted impact on coral reefs. It is a strong defense of recent observations and experiments that indicate that the degree of ocean acidification expected through global warming does not pose a catastrophic threat to corals.

Some additional thoughts I had.

Many coral species in experimental conditions show enhanced calcification rates at higher pCO2. That may happen because dissolving more CO2 in water increases the bicarbonate content of sea-water among other dissolved inorganic carbon species providing a source for CO3 to bond with Ca to form the skeletal material.

This is the representation:

CO_{2 (aq)} + H₂O H₂CO₃ HCO₃^- + H⁺ CO₃^2- + 2 H⁺

So as pH increases so does the bicarbonate (HCO3) content of sea-water.


Just a reminder that decreasing ocean pH and calling it acidification does not mean that the oceans will becoming technically an acid, that is having pH below 7. In fact they will becoming less alkaline from the current pH of 8.1 to about 7.9 or so projected several decades on. This is within the range of variation in pH of seawater inside the coral body cavity and at the interface of the tissue and calcification sites. In other words organisms have already built in mechanisms to handle fluctuations in pH within certain limits.

Off course if pH keeps dropping, at some point the dynamics will change and calcification will be affected. That is because at the site of calcification bicarbonate (HCO3) is stripped of its proton (H+) and the carbonate used to bond with Ca. The proton has to be transported away from this site of lower pH (higher H+ activity) into the coral body cavity and beyond which is at relatively higher pH (lower H+ activity). If sea-water pH is lowered so will eventually the pH in the coral body cavity as there is an easy exchange between the two. The gradient in pH between the body cavity and the calcification site will decrease and that will hinder the transport of H+ away from the calcification site. With H+ building up at that site it becomes harder to strip more protons from HCO3 to form CO3. What that pH range is and whether such pH conditions will ever be reached in the natural oceans due to global warming is not very well understood.

Still there are other dangers to corals from global warming and the most important seems to be coral bleaching caused by the expulsion of symbiotic algae. This may happen as the temperature of water rises causing some internal mechanism within the coral to expel algae or via invasion of the coral by other parasitic microbes that may expel the algae.

Coral metabolism is tightly coupled to the health of this photosynthetic algae and CO2 released through coral metabolism contributes according to some estimates about 70% of the carbon for building skeletons. The other 30% comes from the sea-water HCO3 I mentioned in the earlier para. So removing the algae and degrading the metabolism of the coral would mean cutting off a significant supply of carbon for skeletons.

Again the effect of all these parameters have been demonstrated in experiments that have run from a few tens of hours to a few weeks. For example how important this metabolic source of carbon is in the long run and whether different coral species may be able to harvest more and more carbon directly from sea-water bicarbonate in case the supply of metabolic carbon is shut off is an interesting question.

Likely there will be coral species who will have flexible mechanisms to harvesting carbon. They will flourish and others who have no physiological flexibility might die off.

Nature is resilient due to its variability. The community structure of coral reefs may change over the next few hundred years. But corals as a group will live on.

Meanwhile there are many local dangers to coral reefs in the form of overfishing and destructive fishing methods, turbidity due to increased coastal runoff, nutrient overdose leading to algal blooms that have choke off the corals. As Matt Ridley's article reminds us, these have the potential of wiping out many coral reefs faster than global warming might.