Last Post: The Warehouse

The Beach in Lima

In Peru’s capital city I take an actually hot shower, drink a vanilla latte from Starbucks, and contemplate surf school.

Lara, Mike, and Astrid have come to Lima to facilitate getting the seismometers through customs—the second hurdle after getting the American shipping company to send them.

While Lara tackles her email, Mike and I spend some time exploring the waterfront. It bears a striking resemblance to Santa Monica, CA, though Laura points out that the expensive apartment buildings lining the beach are built on a crumbing cliff of sediments.

Skyline with Paragliders

The park is full of street vendors who want to tell us about their visits to New Orleans, Portland, and LA. paragliders spin upwards from the cliffs—only 150 Soles for a fifteen-minute ride. Down on the rocky beach, men walk up and down advertising surf lessons. Even though it’s only early spring, surfers dot the waves.

After our first day, we get word that we won’t be able to see the seismometers until the day after they arrive, so we start to make plans to fill in the extra day. Lara wants to see the inquisition museum, and Mike convinces me I should go paragliding.

Luckily for both of our stomachs, we get a call the next morning that defies our expectations—not only have the seismometers landed, but we will be allowed to see them. What’s more, the shipping agents are willing to begin the process of checking over the shipment, a process that includes checking the serial numbers of all the instruments, solar panels, and cables at least twice.

Walls in the Park

For me, the call comes in the nick of time, since it’s my last day on the trip. After waiting all morning, the right piece of paperwork arrives just as the shipping agents are going out to lunch. We decide to go with them, and we eat delicious ceviche in a restaurant with a combined seating area/parking lot.

Back at work, they finally let us into the warehouse after stripping me of my camera. The seismometers are there, stacked in blue, gray, and black boxes, and at this point I half expect them to be emitting the mythic glow of lost treasure. Lara runs over and wraps her arms around the nearest box.

In the next five hours, we check off each of the hundreds of parts of the shipment, all the way down to itemized cables and bolts. Thanks to Mike and Lara’s knowledge of the equipment, we finish in hours what would have taken the shipping agents days. Now all that’s left is to get the instruments through customs, but with the list itemized and checked, we’re hoping it will go as quickly as possible.

Surf School!

We end the day at a cozy Italian restaurant in our neighborhood—the same restaurant Lara and Maureen frequented when the PULSE project was conceived. We toast the arrival of the seismometers, which hopefully will soon be in the ground, collecting the data that will give Maureen, Lara, and Susan a new glimpse into the inner workings of the earth’s mantle.

The next morning, I watch the beach get smaller and smaller as I take off for Newark. At last, the seismometers are on the ground, and, after a few hours, so am I.

It’s been an amazing trip—thank you to David Bercovici, Maureen Long, Lara Wagner, and Susan Beck for making it possible.


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Burning Fields and the Bolivian Border

Leveling the Barrel

Each Peruvian town has its own trademark.

On a three-day road trip, our first stop is in the town of the bike cabs, where bike wheels fill the streets five abreast on market day. Here, Astrid finds the first bookseller we’ve seen. She returns to the car with a pile of reading material ranging from children’s history to a novel by the Peruvian Nobel Laureate, Mario Vargas Llosa.

Next, we drive to Yauri, an isolated herding community with a huge American copper mine just over the hill. The town is close to dry, and we find the president of the community in line to get his water rights, the back of his hand marked with a red 26. He’s happy to have a site at his house, and he’s especially happy to have what’s left in our water jugs after we mix the concrete.

The lack of water isn’t the only problem in this town—as we look around, all the fields are burned black for several miles. The president tells us that the fields burned on election day, and no one in the community could get past the flames to vote. Though they believe the fire was no accident, they wouldn’t say who caused it. Now they are hoping for rain to re-germinate all the feed for their livestock.

The President's Wife Takes Us through the Fields

Towards the end of the digging, the wife brings her grandson over, and Mike amuses him by imitating pigeons, fishes, and flies. Mike also holds the level to the mud brick walls of the house. Apart from slight bumps in the material, they’re perfectly straight.

The road to get to our next site is neither straight nor paved, so we wait until day two to drive to Moho—“The garden of the Altiplano” on Lake Titicaca. Based on the assortment of modern steel and glass around the plaza, we judge that flowers aren’t the only commerce. Unfortunately, we turn out to be right. Though the Alcade of the town initially seems willing to help us, he can’t be convinced that we’re not from a rival petroleum company.

He hands us off to the town’s meteorologist, David, who is very well dressed for a weather man.  David climbs in the truck to show us around, but instead of taking us to a site, he tells us to drive further and further out of town. We pass small communities of fishermen as well as trout farms, finally ending up in a town not five kilometers from the Bolivian border.

Lake Titicaca

The weatherman wants us to talk to the mayor of this town, but he’s involved in a cultural ceremony. Lara doesn’t want a station this close to Bolivia anyway, and Astrid is worried about the political stability of this area. She says this is a place where people are not nice, and where they take justice into their own hands. Leaving town, we pass the biggest government building of all: the battered women’s shelter.

As we drive the meteorologist back, it becomes increasingly clear that he thinks we’re lying about something. After stopping us in an unfamiliar part of town, he gets out without pointing the way back to the main square and tells us he doesn’t want to help. Then he tries to take our picture. Astrid is quick to tell him he can’t.

After grabbing a quick lunch of grilled chicken and corn from a cart on the street, we clear out of town. Around a hairpin bend, clusters of soldiers guard the road with guns on their backs. Lara remarks that they’re watching the road from Bolivia to make sure nothing slips by.

We pass them and drive north to Rosapata, the town of the earthquakes. The mayor is hanging out in the town square in track pants, and he immediately agrees to help us find a site. He takes us to an old school now used as a warehouse, and we start digging in the back of the unused playground. The mayor tells us that they recently had a month of small tremors, and the people are scared.

The only shaking we encounter is from some serious off-roading as we move west toward Cusco. Despite its citified appearance, Carlos’ van can handle some pretty big ruts, especially on the way to our last two sites. To get to each, we drive across hoed fields to reach the houses.

Both stations are in herding communities, and both are at farms with lambs, puppies, and baby pigs. The animals are so cute that Jenny and I take a break from digging to play. Bit by bit, the holes are carved out of the rock. At our last site, the mountains sweep up from the grass of the valley, cupping an alkaline lake where pink flamingos are eating.


Before we can load the vans, the owner of the house runs out with a bowl of toasted grains for us. It tastes a lot like popcorn, and it makes a sharp contrast with the unfriendliness at Moho the day before. But on the drive back to Cusco, just as we start to forget, we see a bright line of fire wrapping the side of a hill.

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Adventures in Styrofoam

El Container

For most people, a cookie is a dessert. For seismologists, that definition has to be revised to include circular discs of Styrofoam which are used to insulate the delicate instruments.

Since we’re still in Cusco, we spend the morning shopping for sandbags, tarps, duct tape, a rock bar, sharpies, and another bucket for mixing cement. The initial plan was to return to Cusco tomorrow, but since Lara needs to be in internet contact to facilitate the transport of the seismometers through customs, she decided not to go out into the field. And without one of the leaders of the project, we can’t pick sites or put in barrels.

However, we can get everything ready for when the seismometers do arrive. This entails buying huge sheets of ceiling insulation, strapping them to the top of our van, and driving them to our storage container.

Streets of Cusco in the Rain

On the way, we encounter a minor difficulty when one of the wheels of the van falls into a ditch. There is a two foot hole in the road between two grates, and the back axel is resting on the ground. Fortunately, ten men appear out of nowhere, grab the back end of the van, and lift us free.

Once we arrive, we use razorblades to cut “cookies” out of the insulation. These Styrofoam discs will be stuffed into the barrels, where they will sit over the seismometers to keep them from getting too hot or too cold. If the temperature fluctuates, the equipment will have less accurate responses to seismic waves, and it will be harder to tell what’s going on inside the earth’s crust.

Though machines might consider these cookies sustenance, us humans have to look farther afield. Back in town, Jenny, Mike, Ryan, and I decide to try guinea pig. The restaurant brings them to us whole on the plate, with tomato and cucumber Inka helmets. After we’ve had a chance to snap a few photos, they whisk the plates away again for carving. When they return, I pick up my knife and fork, but the waiter shakes his head.


It turns out that guinea pig has to be eaten with the hands. As I pick up a piece (amidst many jokes about killing Fluffy) I discover that these rodents taste a lot like a chicken leg. Nonetheless, I’ve never felt more like a carnivore.


On the whole, it’s pretty tasty, but I don’t think I’d order it again. When the waiter asks us if we want dessert, we ask him if he has any hamsters. Luckily, he doesn’t understand us.

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A New Plan

Since we’ve been in Cusco, I’ve learned that the Spanish for duct-tape is duct-tape, that concrete can only be bought in 45 kilo bags, that pisco sours are delicious, and that the hills above Cusco boast an Inka temple of the moon as well as a gigantic floodlit Jesus.

But starting tomorrow, we’ll be going out into the field again. The team is splitting into two groups to put in barrels for the last few PASSCAL sites. Me, Lara, Christine, Astrid, and Jenny will be in the mountains between Cusco and Arequipa, while Kumar, Mike, and Victor will be in the jungle near Manu.

Hopefully, after four days of digging, we can return to Cusco for the arrival of the seismometers. Look out for a new post then with details of our mountain adventures!

The first team will put barrels in the top six yellow dots. The second team will finish the blue dots.

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A Hitch


For the kind of data Lara, Maureen, and Susan want to collect, STS-2 seismometers are the best in the world. Unfortunately, they’re not here yet.

The problem is that it’s inadvisable to ship the instruments until we have a good chance of getting them through customs in Lima. We’re trying to complete all possible paperwork that might be required for 60 seismometers to enter the country, but it’s not obvious what the requirements will be. At this point, we hope to have the machines by next Tuesday.

Dome shaped STS-2 Seismometers work by measuring electric current. Inside each one are three weights (or masses) which are held in place by a charge that runs through them. When the ground shakes, the outside of the instrument moves, but the current holds the masses in place. By measuring how much current is required, the seismometer records the size of the waves.

While they are in the ground, the masses hang down without touching the plates on either side of the dome. While they are in transit, the masses have to be locked to one side or the other. If they are left unlocked and allowed to swing, even picking one up is enough to break the delicate pivots holding the weights in place. Each pivot costs over $100, and if one breaks, there are only a handful of people in the world who know how to fix it. When the machines arrive, we’ll be able to test the whole group—then we can start to install them in the barrels we’ve prepared.

Lara’s priority is to install the seismometers that are on loan from PASSCAL first, because they have to go back in September 2012. Many of them are also going in areas with roads that will wash out in the rainy season, so the stations have to be assembled soon or the sites won’t be accessible until next spring.

Machu Picchu

Since we’ve been in Cusco, we’ve put one more barrel in, but apart from that, we’re mostly done until the seismometers get here. What’s left is to permit a few more sites on national park land, but it’s election day, so all the officials are busy.

Amtrak, Take Note

With this in mind, Lara gives us a day off, and Jenny, Christine, Lara, and I jump at the chance to go to Machu Picchu. To get there, we take the train to the base of the mountain and then a bus to the ancient city. The trains are beautiful, with huge plate glass windows so passengers can see the mountains.

First Moments at Machu Picchu

The tracks follow the Urubamba River up the Sacred Valley of the Inkas, where they built 100 temples in the shape of constellations. Our guide tells us that they hoped to match the Milky Way, creating harmony between the river in the sky and the river on the earth. Inkas were required to make a pilgrimage to Machu Picchu once in their lives, and carried offerings of stones from far away places.

Walking around the city ourselves, we come to the astrological observatory, which has a central sculpture depicting the compass points. Not only did the Inkas know true north, but they also added a lower point for magnetic north. At the winter solstice, the shadow of the stone makes a triangle on the ground. In the exact center of the triangle, they carved a circle, creating a symbol exactly like the Masonic eye on the dollar.

The Famous Rock

Lara wants to put a seismometer up here, and though they haven’t arrived yet, at least the delay allows us a second hitch—this stone the guide calls the hitching post of the sun.

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Lara, Lake, Truck

Altiplano literally means high plains, but here the grass covered hills rise out of the valleys like sand dunes, and a cold breeze blows down from snow on the peaks. Crossing a pass, we hit our highest altitude of 4,800 meters—roughly 15,700 feet.

I’m not feeling the effect of the altitude, but when I look in the mirror my lips are blue from lack of oxygen—the same blue as the painted houses that dot the land. Women in hoop skirts, shawls, and felt bowler hats tend the herds, leaving their children on blankets in the grass.

The Peruvian Stroller

The Peruvian Stroller

Coming down the mountains a little, the grass gives way to Eucalyptus and fir trees, and we find a site at the edge of a village. Children are effortlessly playing tag in the street, but Lara and I find ourselves out of breath as we carry buckets of water for mixing cement. We hit bedrock about two feet down, which means the data from this site will be good—but we can’t put a barrel into the ground. A little ways up the slope we try again, and this time we succeed. Since sediments pile up on top of the bedrock, and seismic waves get distorted when they pass through sediment, a barrel sitting on bedrock can collect data that more accurately portrays what’s under the crust.

We don’t want to drive after dark again, so we quickly pour the concrete, and beat it back to Makusani, the self-proclaimed alpaca capital of Peru and the world. The restaurants around the square advertise alpaca meat, and the church tower vies with rickshaws for attention.


The next day, we attempt to permit a site (to find a person willing to let us dig a hole on his land), but much of the area outside town is populated by herders who don’t own the grasslands they use. People also seem to be suspicious of the project because of exploitation by mining interests which we have nothing to do with. Between that uneasiness and our lack of a Quechua speaker, we can’t find a site though we try for hours. Eventually, Lara calls it a day because she’s not feeling well, and we head back to Cusco.

On the way back to town, we get a firsthand glimpse of the problems of the new highway between Juliaca and Cusco. We see two fatal motor scooter accidents, and a dog hit by a car. Just when we think we’ll make it back with no more, we have to watch as a mule’s foot gets run over by a bus. The problem seems to stem from the fact that the small agricultural towns use the highway as the village street, but other drivers use it as one of the few good straight roads.

The Plaza in Makusani

After unloading the trucks, we arrive at the hotel. For the first time in days, I have access to vegetables, internet, and chapstick for my no longer blue lips.

Cusco by Night

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Lilies on the Staircase

We wake up to the sounds of jungle birds, street peddlers, and highway workers starting their day. The hotel we’re staying in is run by a family with three adorable girls and a gatito, but we can’t stay for breakfast.

Instead, we drive to a rest stop by the side of the new highway. While it might seem counterintuitive to Americans, this rest stop is one of the nicest places we’ve found in the jungle, and they give us coffee they have grown and roasted themselves. Out front, they have a wheelbarrow full of fresh pineapple that they blend into juice. This particular café is part of an initiative to build more sites like these—and the construction was subsidized by the same contractor that is building the highway.

Christine, Lara, and Victor at the rest stop with la familia Mendez

After such a great start, we dig two sites in one day—the first at a farmyard with baby chicks, and the second at a ranch with monkeys in the trees. Back in the car, I spot a woman on the road walking with a pet monkey wrapped around her leg.

As we drive, Lara explains a little more about shear wave splitting, one of the foci of Maureen’s research. She tells me that when these seismic waves hit a rock at an angle, they can split into two smaller waves, and one may go faster than the other, depending on the composition of the mantle rock. Most seismologists assume this difference is negligible, she says, but not Maureen. Instead, Maureen measures the time difference to calculate which piece of the wave is moving more quickly. Then she uses the faster wave to determine which way the mantle is flowing.

Lara adds that data for shear waves is only one piece of the information she will receive from installing these seismometers. Other attributes include the depth of the crust before it becomes the mantle, and the physical makeup of the mantle itself. For the latter, seismologists need to collaborate with geochemists who can help to puzzle out the chemical makeup of the earth’s interior.

Three hours into the drive, we realize we’re not as close to a town as we should be, and it’s getting dark. As night falls, we’re still winding our way into the mountains on a dirt road which is under construction. We pass two places that look like towns, but Victor realizes they are just camps for the highway workers. Looking at the GPS, Lara can see a village about 40 minutes away. We hold our breaths, and with the help of our excellent drivers Luis and Edwin, we make it. Lara is relived, and declares that we’re never driving after dark again.

My Hand at Our Second Site

Though we started in the 90 degree heat of the jungle, we get out of the car to 50 degree mountain air. Our hostel has rooms up a mouldering cement staircase, and the shower consists of a sink and a bucket. However, it’s still spring in the mountains, and the most beautiful Calla Lilies are blooming by the side of the stairs.

Morning in the Mountains

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A Market on the Way out of Cusco

My first trip out of Cusco starts at 5:15 with a quick breakfast of eggs and coffee. Before we get on the road, we stop at the container—a rented shipping crate in a vacant field that Lara uses to store all the supplies for each site. Since the seismometers haven’t arrived yet, we’re getting the ground ready for them by digging holes for the plastic barrels that keep the machines waterproof.

We’ve hired three drivers, two for the half of the group that includes me, Lara, Professor Victor Aguilar from the Universidad National de San Agustin, and Christine Worthington, one of Lara’s graduate students from UNC. The other group—Jenny Hanna, a student of Maureen’s, Mike, and Astrid Martinez, a friend of Lara’s who is here to translate and help out—has a van to themselves.

We load four types of shovels, two types of cement, and five barrels into our trucks. After clearing the edges of Cusco, we start to climb over a high pass. I can see snow covered mountains in the distance, and alpaca and sheep farms line the highway. A woman and two children come out of a stone house to beg, lowering cupped hands towards the road.

Laundry Day

This particular road used to be known as the worst in Peru, but it is currently under construction, and large parts of it are now paved. We arrive at a possible site much sooner than expected, and a family agrees to let us put a station in their chicken yard.

There are boulders everywhere, and the man who owns the property tells us that an avalanche deposited them all over his part of the valley. The rocks are not only on the ground, but they are also underneath it, and digging the hole for the barrel proves somewhat challenging. Lara, Christine, and I are all ready to work, but the drivers, Victor, and the owner are reluctant to let us women dig. Victor smiles and points at the men. “Hombres machos,” he says.

Lara ignores them and grabs a rock breaker, earning herself the title of “trabajera.” Some of the rocks are probably 200 lbs, so Lara strikes a compromise. “Les hombres les rockas, les mujeres la terra.” This seems to satisfy everyone, and in between rocks, Christine and I start digging.

Lara and Victor mix concrete. Luis and the property owner look on.

When we’re done, we mix concrete and pour it into the hole. Then we put the barrel in, level it, and add more self-leveling grout on the inside. The concrete on the outside keeps the barrel stable, and the grout keeps the inside level as well. The leveling is to insure that when the seismometer is placed inside the barrel, it will be able to correctly read which seismic waves are coming vertically through the mantle, and which are coming horizontally through the crust.

After we get the site prepared, I climb in the car with Victor and he hands me a Spanish-English dictionary. As the landscape outside the car changes, I learn enough to ask him what kinds of trees are in the jungle on either side of us. He tells me there are plantain trees and coconut palms.

Birds' Nests Hanging from a Tree

The road also winds along a river, and the construction has created a lot of loose soil which miners downstream pan for gold. That night, we stay in a mining town that could have come straight out of the American west circa 1860. The only grown women in evidence run hotels, laundries, and restaurants. The main drag is studded with pay telephones and gold buyers for those who strike it rich.

At dinner, Lara pulls out her computer to look at sites for the next day, and three children from the town gaze over her shoulder. She turns on photo booth, and lets them take pictures of themselves with silly faces.

Amazing Photobooth

On day two, we drive deeper into the jungle to Puerto Maldonado on the Madre de Dios River–one of the tributaries of the Amazon. The road here was supposed to be closed, but for a few soles, the policeman on duty lets us through. Even though it’s under construction, the road is good, and Lara jokes that we’re lacking in adventure.

Though she initially wanted to put a station near Puerto Maldonado, she decides to go a little bit north of where we are in order to line up the station with others in the array. She explains that there are two ways to create data from imaging—either with a grid of sites which makes two dimensional images, or with a scatter plot which creates three dimensional ones with slightly less accuracy. Her arrays are a hybrid between the two, with some grid lines and some intermediate points.

The images themselves come from the seismic waves which move through the earth at different speeds and angles. From these differences in speed, Lara can figure out how thick the earth’s crust is and whether the parts of the mantle she’s looking at are hot and melted or cold and solid. The hardness of the rock is reflected in the speed of the waves, so this can also give her clues about the properties and types of rock within the mantle.

Stage 1

At the end of the day, we find a site at a farm, but it’s too late to start digging. We drive back to a town called Santa Rosa, passing what Lara calls a “boomtown.” The buildings are made from beams and tarps, and the town is populated by mostly men on motorbikes. Women advertise bike washing, food, and before the town is over, a tarpaulin strip club.

Stage 2

Santa Rosa itself has run dry, meaning that there is no running water anywhere in town. Most of the people seem to be out on the sidewalk, buying fried rings of dough and fresh fish from a traveling vendor with a speaker on the hood of his car. We continue to the next town, which has no power, and find ourselves a shower and some food.

Stage 3

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Golden Bricks and Guinea Pigs

Cusco and the Ruins of Qorikancha

I begin my journey to Peru at New Haven’s Union Station. Instead of the usual overnight bag, I’m equipped with a suitcase of clothes, a bag of camping gear, and a giant blue duffel full of 65 rubber gaskets for installing seismometers.

Everything goes pretty smoothly until my plane from Miami to Lima is delayed by over an hour. Getting on the plane, I realize I will probably miss my connection to Cusco, and I have no idea if my bags or my group will still be at the airport. Though I haven’t met the team leader Lara Wagner yet, I’ve seen her picture online, so I’m hoping to find a recognizable face.

Another member of the group, Mike Fort from the PASSCAL instrument center in New Mexico, is also arriving, so I know to look for him as well. Thinking that he might be on my flight from Lima, I start looking a little too hard, and ask a random Peruvian man if his name is Mike. I walk away from this awkward interaction, but unfortunately, when we get on the plane, he’s assigned the seat next to mine.

The Real Mike Fort

Luckily, Lara is waiting for me at the airport, and a driver and a porter pull my bags off the conveyor belt. On the way to the hotel, I catch my first glimpses of Peru out the window. Advertisements for Inka Cola (a soft drink) and Somos Peru (a political party) abound in equal profusion.

Once I’ve dropped off my stuff, Lara sits me down and tells me a little more about the plans for the week. Starting Sunday, the group will split up for six days in order to cover more ground. I’ll be travelling for seven days through the jungle to Puerto Maldonado, a town 34 miles from the Bolivian border in the Amazon rainforest. The seismometers have not yet arrived yet (clearing customs requires that the descriptions of the machines and all of Mike’s correspondence about them be translated into Spanish) so we will be setting up sites, digging holes, and pouring concrete into waterproof barrels where the seismometers will eventually go.

After filling us in, Lara gives Mike and me some time to walk around the city. It’s a beautiful day, and since the local time in Peru is only one hour earlier than the local time in New York, neither of us are jet-lagged. We stop to visit a monastery on the site of Qorikancha, an ancient Incan temple of mortarless stone. Lonely Planet tells us that when the site was in its heyday, the stones were covered with 14 karat gold.

On day two, we wake up to a breakfast of round bread, strawberry jam, and coca leaf tea. Then we’re off to look at potential sites with a seismologist from Peru. We drive out of the city in a packed van, passing stands of Eucalyptus trees and a gigantic floodlit Jesus with hands outstretched over the city. After a while, the land turns to farms, and kids chase our van through a small village.

Street Scene

To get to the possible site, we have to climb to the top of the hill, and at 14,000 feet, all of us are out of breath. “Who needs air?” Lara jokes. The view overlooks a reservoir, and a huge rift snakes across the opposite hill. Mike explains that this is a good location for a site because we are close to the bedrock. This means that the seismic waves moving through the ground can be picked up more easily, rather than diffusing into softer ground.

Lara likes the site in theory, but it doesn’t meet two of her requirements. The road to the top is probably too rough for a truck, and there are no houses around to watch over the seismometer.

After climbing down the hill, we head back to town where we spend the afternoon shopping for food and supplies. The stores are grouped by what they sell, and we visit the grocery, hardware, and plastic bucket districts.

Trying on an Alpaca Hat at a Street Fair

At dinner, everyone is talking about Guinea pig or cuy, the local delicacy. Though I don’t try it on day two, it’s definitely on the menu.

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Fingerprints of Flow

A Map of Peru with Sites for Seismometers Marked in Red

Two weeks ago, I returned from a field trip in the Big Horn and Seminoe mountains of Wyoming. Two days from now, I’ll be in the air on my way to Cuzco, Peru. The city functions as a gateway to the ancient site of Machu Picchu and as a bunkroom for hikers on the Inca Trail. But for me and for Assistant Professor Maureen Long, the city is the starting point for an even more unusual exploration.

Thanks to Professor Long and Professor Bercovici, I am going as a field assistant on another Yale Geology and Geophysics field trip. This time, I’ll be spending three weeks installing seismometers—machines used to gather data on the seismic waves that move through the earth. The goal of the project is to use this data to understand a Peruvian subduction zone.

In a typical case, subduction means that one plate is sliding under another and eventually sinking back into the mantle. Volcanoes spring up at these sites, because the decrease in pressure when the plate sinks causes water that has been baked into the rock to come out, lowering the melting point of the rock. Melting also creates bubbles of gas that rise and pressurize volcanic eruptions. In Peru, however, the bottom plate only sinks for approximately 100 km before flattening out for 500 km. This flat slab presents a host of questions.

For example, how did a slab like this one form in the first place? What does this kind of plate movement do to the crust above it? And what keeps the slab from sinking?

Though geologists have looked at other sites in Chile and Argentina where the buoyancy of the sea floor may be causing a similar phenomenon, that explanation doesn’t work for Peru. And since the slab prevents volcanic activity that typically accompanies a subduction zone, where does the water go when the plate begins to melt?

For Professor Long, the answers to these questions lie in examining seismic waves as the fingerprints of mantle flow. She can trace these fingerprints because crystals in the mantle rock point in the same direction the mantle is flowing. Since waves move fastest in the direction the crystals are pointing, wave speed can provide an indication of mantle flow direction. In looking at patterns of seismic waves, Long can determine whether they are moving quickly or slowly through a certain part of the mantle—and from there she can gather information about the mantle flow around this particular slab.

Long can’t come to Peru herself since she’s expecting a baby in mid-December, but her collaborators on the project, Lara Wagner from the University of North Carolina and Susan Beck from the University of Arizona, will be leading the trip. This May, Long will get a chance to go back and extract the data collected by her seismometers.

In the meantime, I’ll be helping to dig holes and install these machines in the areas around Cuzco and Lima. The arrays will stretch almost to the Amazon, and many of them will be planted in the backyards of cooperating Peruvians.

After the nurse at the immunizations clinic put a live Yellow Fever vaccine into my arm, she asked me how I felt. I smiled and replied, “Like I’m really going to Peru!”

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