Bill Menke and Enrique Triep’s Andes Pilot Experiment trip, January 1997.

This summary was compiled by Bill Menke on February 24, 2010. I have no journal, per se, for this trip.

Here is a paragraph from a proposal written in 1998 that follows up on the trip: “In order to assess the viability of a large seismic experiment in this part of the Andes, one of us (Menke), in conjunction with Seismologist Enrique Triep of the National University of San Juan (Argentina), conducted a small, prototype experiment in the field region. We drove 3300 km of roads and found them to provide excellent access to the region, and found many sites appropriate for seismometers. We operated a single broadband seismometer (REFTEK 72A07G / Guralp CMG40T) for one day at each of seven sites, during which time we recorded 150 regional earthquakes and two teleseisms. We will discuss some of these data below. Our overall conclusion was that this region is well-suited for a seismological field experiment.”

I flew into and out of San Juan, Argentina, and visited the University there, where Enrique works. We then took a Ford F150 truck on a tour of the section of the Andes from just south of El Toro Mountain to Maipi Volcano. The order of sites was (more or less) San Juan (a small city); Tudcum (a village just east of the Andes), the Cura Valley (high in the Andes, where we stayed at the Sepaltura National Gendarmeria (civil defense) post, Carmen Camp (also in the Cura Valley), an epithermal deposit gold mine near Zancarron Pass (west of the Cura Valley, Tudcom again, a small mine near a Gendarmeria post on Highway 150 west of Las Flores (a small town), San Jose de Jachal (a largish town), Huaco (a small town), Jacal (again), Mendoza (a small city), the Condar Gendarmeria post (for coordinates, see SEIS6 below), Maipo volcano, and then back to San Juan.

We took several interesting day hikes: A little granite pluton that stuck out of the more-or-less-level alluvial plane between Tudcom and the eastern edge of the Andes; a stretch of rugged Andean mountains near the small mine mentioned above; and Maipo Volcano. In the Maipo hike we camped for two nights at the Laguna del Diamante (a lake near the volcano, about 3200 m elevation) and climbed up the volcano. We did not reach its summit, but only the slope break, at about 4300 m elevation, between the relatively gently-sloping lower part of the volcano, which is dominated by lava flows, to the steeply-sloping upper part of the volcano, which is dominated by tephra. Many of the lava flows that we crossed were composed of meter-to-three-meter rounded blocks of what must have been very viscous lava. We took a close look at an eruptive vent of one of them; it was huge, much larger than the ones I have seen in Iceland, even at Laki.

I slipped on loose gravel on a steep slope on the second of these hikes and cut open my left knee. I went to a local doctor and received three stitches and a tetanus shot.

I kept a field notebook that recorded the locations of the seven seismometer sites that we occupied:

SEIS1, near la Casona, 09 Jan 97, 30 09.897S, 69 28.508W, 2800 m

SEIS2, near Sepaltura Gendarmeria post, 10 Jan 97, 29 50.257S, 69 42.224W, 3725 m

SEIS3, near Carmen Camp, 12 Jan 97, 30 02.947S, 69 47.698, 3914 m

SEIS4, in a mine 30 m into hillside, 14 Jan 97, 30 23.817S 69 34.409, 3010 m

SEIS5, in building behind hotel west of Huaco, 15 Jan 97, 30 08.314 68 32.632 1170 m

SEIS6, near Condar Gendarmeria pos, 17 Jan 97, 32 01.689S, 69 45.745W, 2034m

SEIS7, near Maipo volcano, 19 Jan 97, 34 10.142S, 69 43.016W, 3212 m

Each seismic station was operated for about a day. All locations are in the WGS84 datum.

Here are two maps from my log book. The one on the left is of the Cura Valley, and I based it on a geodetic-quality map that I examined while in San Juan. The second is of the area around the Condar Gendarmeria post and is just a sketch map. The left-most square is the post. The X marks the spot where we got the truck stuck in the mud at a stream crossing. We worked several hours trying to get it out, to no avail, but fortunately a group of men on horseback happened by. They showed us some tricks for dealing with mud, including covering it with loose, dry sand. Then they and we pushing together were able to get the truck out.