sfb-574

Student helper wanted / HiWi gesucht!

The homepage of the whole Sonderforschungsbereich (= National Research Center supported by the German National Science Foundation DFG) is here. Please check there to find out what this huge project of Kiel University and Geomar is all about! You will also find maps and updates on recent expeditions and results there.

Ernst Flüh and me are the leaders of subproject A2 "Coupling and mass-transfer between upper and lower plate". Roughly, Ernst takes care of marine operations and I am responsible for the onshore operations, i.e., the land based seismological network. Accordingly, you mainly find information about the latter on this page.

See most recent results here.

The proposal for the 2nd phase of the SFB has been submitted (November 2003) and the report for the 1st phase finished.

The proposal for the 2nd phase has been evaluated favourably (Jan. 2004).
Testing of a prototype borehole sensor to look for non-volcanic tremors in Costa Rica has started.

Some general figures from the SFB home page

	Material transport and transformation in subduction zones: Long- and short-term trends of the Earth’s climate, geochemical evolution of the exosphere, and the causes of certain natural hazards are related to the reactions of volatiles and fluids in subduction zones.		Geodynamic setting off Central america; tectonic elements and characteristics of the segment off Nicaragua and Costa Rica provide different material inputs and conditions which would result in different volatile and material reflux scenarios.
	Lithospheric characteristics are illustrated in 4 cross sections; the differences include dip of subducting slab, earthquake focal depth, temperature, highly faulted outer rise off Nicaragua, crustal segments formed at the East Pacific Rise and at the Nazca-Cocos spreading centers, respectively; seamount province, and plate alteration through the Galapagos hot spot.
	Subduction erosion along the convergent margin off Costa Rica; from Ranero and von Huene (2000). Tunnelling by seamount subduction and breaking off of large rock lenses along the décollement are two important mechanisms affecting material transport.		The deep-sea trench, a highly complex continental margin, and the relief of the oceanic plate are the major morphologic and tectonic elements of a subduction zone. Off Costa Rica the division and complex structure of the wedge and slope result from slumping, seamount subduction, sediment influx from the fore-arc, and accretion of sediments riding on the oceanic crust.

Amphibian seismological network This network was deployed in April/May 2002 and will operate until October. Main purpose is the observation of micro-seismicity associated with subducting seamounts.

Download a Postscript version of above figure here [361 KB] .

Deployment of land stations in April 2002.

	The seismology lab at ICE in San Jose (Apr 4, 02).		Lots of stuff...
	... needs a big truck.		Yes, we're in Costa Rica, heading west to Jaco at the pacific coast.
	Base camp in Jaco, our two cars being loaded.		Sensor setup is a delicate matter - Mark L-4C-3D seismometer just before being buried.
	These special drums are cemented into the hole. There is also a 15 cm concrete layer inside the drum.		Water tight drum resp. lid just before being covered with earth.
	A typical station setup inside a house. In the box: Digitiser, harddisk unit, charger, charge controller. Outside: Backup battery, various cables (power, sensor, GPS, earthing).		The (incomplete) crew: Jürgen, Ricardo, Ivonne, Chico, Guido, Didier (left to right).
	Lots of problems require a clear mind and a clear sky (for GPS reception)...		Cable making day (power cables, earthing cables, GPS cables,...)
	Unusual location in nursery requires bird cage to protect charger from children as well as to protect children from charger...		... and also requires relocation of one inhabitant ...
	Our smallest station setup resulted from joining the existing accelerometer setup at Quepos.		A sceptical spectator.
	Where there's no power, we'll use solar panels. But where there's no support, we'll have to have something welded by the road...		Our only solar powered station. This is a shed for drying wood.
	Station "pina" where even the sturdy Mitsubishi couldn't go anymore.		The usual fare - so-called roads in the jungle.
	Oops. Note the chain that prevents the car from sliding into the gorge.		The driver wouldn't have found this funny (luckily he'd run off, looking for help).
	This is all soo tiring!		A foretaste of rainy season.

Oct. 2002: Moving the network to the Quepos region

It's rainy season!

Preliminary report on onshore activities

1) April/May 02 – October 02 (“JACO-NET”)
13 stations initially, later 15; one solar powered.
Network extends from Caldera/Tivives (W) to Quepos (E), i.e. ~ 70 km along coast, ~ 30 km inwards.
Status of stations/hardware: 3 hit by lightning, 1 failure of z-component, 2 failures of chargers resulting in temporary data gaps, battery stolen at 1 (last month missing), 2 defunct hard disks (data partially recovered), 2 defunct GPS antennas (=> timing problems). No failures of field computers, no problems with writing/reading of tapes.
Data: 1st 40 days: 1100 triggered events (STA/LTA, minimum of 5 stations) containing 470 earthquakes => quite noisy! Man-made noise is confirmed by day/night comparison. Stations too close to the sea give bad signal despite filtering. A few km distance is sufficient, however.
2nd 40 days: 5600 triggers at up to 14 stations => strongly increasing seismic activity, also because of M=6.4 eq SE Quepos with 300 aftershocks.
1st 40 days were triggered/inspected by JG then passed to HiWi for picking (ongoing). Another HiWi currently inspects 2nd 40 days.
Locations/magnitudes/mechanisms not addressed yet. 3rd 40 days await pre-processing, remaining data up to Oct. still in suitcase…
Active explosion in network (1 to) in Aug., 2nd one in Sept. failed.
Data collection/archiving procedure: disks with raw data > field computer > 2 identical DAT tapes (1 for Kiel, 1 for San Jose). Most recent data always stays on field computer in addition. In Kiel add. backup on tape robot.
Local working conditions: Excellent support from local partner ICE (field workers, scientists, bosses)! Generous contribution of cars, field personnel, costs (fuel, overtime, accommodation for workers etc.)

2) Since October 02 (“QUEPOS-NET”)
Moved field computer from Jaco hotel to local ICE office in Quepos.
Currently 13 stations (2 beyond repair, currently at GFZ).
Network extends from Parrita (W) to Dominical (E), i.e. ~ 60 km along coast, ~ 30 km inwards.
2 station locations were kept for overlap, 11 new locations; 6 solar powered.
Seismometers had to be cleaned of strong corrosion, now spray-protected.
Field team mostly identical with 1st team. Due to ICE financial problems we had to pay overtime this time. Station service assured by new person in charge.

Amphibian network of first and second phase. Red symbols show location of sensons from April - October 2002, blue symbols give network since Oct. 2002.

Some photos of network transplantation in Oct 2002

	Rough planning of new station locations.		Welcome back to the muddy jungle!
	Driving is even more adventurous this time...		...and working much wetter...
	When there's some sun...		... sweating makes up for the rain.
	Grasshoppers like it.		Checking equipment and testing beer in San Marcos.
	A much better contraption for setting up solar panels this time, devised by ICE.		They waited for us in vain - vultures.
	"The competition" - a telemetered station at vulcan Poas.		Actually, it's nice cool up in the mountains.
	And yes, Costa Rica also has beaches (at Cahuita National Park).		... at Manzanillo.

See newest results here.