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by state. Restrictions apply. See site

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for details. Mexico, City's

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metro system is sinking fast. Yours

1:07

could be next. Subsidence.

1:10

Is causing parts of Mexico City to sink

1:12

and it's happening at an uneven rate. That's.

1:14

Bad news for a sprawling public transportation

1:17

system. By. Matt Simon. With.

1:20

It's expansive buildings and concrete. Mexico City

1:22

may not look squishy, but it is

1:24

ever since the Spanish can keep the

1:26

doors drained. Like to go go to

1:28

make way for more urbanization. The land

1:30

is been gradually compacting under the weight.

1:33

It's. A phenomenon known as subsidence and

1:35

the result is grim. Mexico,

1:37

City is sinking up to twenty

1:39

inches a year, unleashing havoc on

1:41

as infrastructure. That. Includes the

1:44

city's metro system the second largest in North

1:46

America after New York City's. Now.

1:48

Satellites have allowed scientists to meticulously

1:50

measure the rate of sinking across

1:52

Mexico City. Mapping were subsidence has

1:55

the potential to damage railways. When.

1:57

You're here in the city. You get used to buildings being.

2:00

That a little says.e O Salon

2:02

A has a remote sensing scientist

2:04

at the National Autonomous University of

2:06

Mexico. You. Can feel how the rails

2:08

are wobbly. Writing. The metro in Mexico

2:11

City feels weird. You don't know if it's

2:13

dangerous or not. You feel like it's dangerous,

2:15

but you don't have that certainty. In

2:17

a recent study in the journal Scientific Reports,

2:20

Salon or Rojas went in search of certainty.

2:22

using. Rate our satellite data. He and his team

2:25

measured how the elevation change across the city between

2:27

two thousand and eleven and two thousand and twenty.

2:29

Subsidence. Isn't uniform? The.

2:31

Rate depends on several factors. The most

2:34

dramatic instances globally are due to the

2:36

over extraction of groundwater pump, enough liquid

2:38

outs and the ground collapses like an

2:40

empty water bottle. That's. Why

2:42

Jakarta, Indonesia is sinking up to ten inches

2:44

a year. Over. In California's San

2:46

Joaquin Valley, the land has sunk as

2:49

much as twenty eight seats in the

2:51

past century due to farmers pumping out

2:53

too much groundwater. A

2:55

similar draining of aquifers is happening in

2:57

Mexico City, which is gripped by a

2:59

worsening water crisis. The subsurface is like

3:02

a sponge. We get the water outs

3:04

and then it deforms because it's losing

3:06

volume Says Salon or Rojas. How.

3:08

Much volume depends on the underlying sediments in

3:11

a given part of the city. The ancient

3:13

lake didn't neatly layer equal proportions of clay

3:15

and sand in every area. That.

3:17

Produces a lot of different behaviors on the

3:20

surface. Salon or Rojas. Subsidence.

3:23

Rates across Mexico City very substantially

3:25

from twenty inches annually to not

3:27

at all where the city is

3:29

built atop solid volcanic rock. This.

3:31

Creates differential subsidence where the Lansing's

3:34

differentially not just square mile to

3:36

square mile or block the block.

3:38

But. Square foot to square foot. If.

3:41

A road, railway, or building is

3:43

sinking differently at one end than

3:45

the other. It'll destabilize. That's.

3:47

How You get the Tilted Road traffic

3:50

barriers that aka Telus station. And

3:52

the deformation of tracks that Oceania station.

3:55

If. In either of these places, the land was

3:57

subsiding at a uniform rate. The tracks and road

3:59

would. I also think uniformly and you might

4:01

not have a problem. We. Found

4:03

that some of the segments of the metro

4:05

system are moving faster than it was designed

4:08

for says salon or of us. The.

4:10

Study found that nearly half

4:12

of elevated segments of the

4:14

metro are experiencing differential subsidence.

4:17

This. Would imply that they would need

4:19

to be serviced before the systems

4:21

typical threshold of fifty years, at

4:23

which point a segment would need

4:25

rehabilitation or repair to continue optimal

4:27

operation. Systemic. They

4:29

transport they pull a Tivo which operates

4:31

the Mexico City Metro. Did not provide

4:34

comment for this story after repeated inquiries.

4:37

A Metro system, by it's nature,

4:39

is a sprawling web of lines.

4:41

Mexico City's includes one hundred forty

4:44

miles of tracks running underground, in

4:46

subways above ground and on elevated

4:48

platforms. It goes from areas

4:50

that are really stable to areas that

4:52

are subsiding at thirty centimeters per year

4:54

or even almost forty centimeters every year

4:56

says salon or of us. So.

4:59

The goal here was to see where the

5:01

most damage could be. That. Damage

5:03

comes in a few forums as the

5:06

land sinks they can create David's for

5:08

rainwater to accumulate, causing flooding along railways.

5:10

That. Can mess with the electrical system that

5:13

powers the trains salon or Rojas says.

5:15

And. Elevation changes can increase the great

5:17

of the rails. The metro trains are

5:19

designed to operate on a maximum slope

5:22

of three point five percent Salon or

5:24

Rojas says, but some stretches of tracker

5:26

now double that due to subsidence. Train.

5:28

Can get derailed very easily if there

5:30

is a slight change in the leveling

5:33

of the railways says Manouchehr Shears, a

5:35

and environmental security expert at Virginia Tech.

5:37

The study subsidence but wasn't involved in

5:39

the new paper. Most. Of

5:41

the infrastructure has certain thresholds, it tolerates

5:43

a certain level of differential land subsidence,

5:45

but often they don't account for the

5:47

rate that we see. For example, in

5:49

Mexico City, So. Our Rojas

5:51

and his colleagues found subsidence in the

5:53

area of an overpass near the Olivas

5:55

station which collapsed and twenty twenty one

5:58

while the metro train was try going

6:00

over it. We. Did part

6:02

of this analysis before Twenty Twenty One

6:04

and we detected that that area was

6:06

having differential displacements says Salon Auto has.

6:09

We. Were like oh yeah, it looks like something

6:11

could happen here in the future. We.

6:13

Think that it's not a coincidence that we found

6:16

this. Salon. Or Rojas was

6:18

careful to say that the potential

6:20

contribution of subsidence to the disaster

6:22

would require further evaluation and official

6:25

investigations Have cited construction errors and

6:27

do not mention subsidence. For.

6:30

This study, the researchers looked at the

6:32

metro infrastructure above ground, not the subway

6:34

segments, basically the parts of the system

6:36

they could verify visually. But.

6:38

By providing the systems operators with

6:40

information on how quickly it's infrastructure

6:43

might be subsiding. Their. Work and

6:45

hopefully inform interventions. Engineers

6:47

can add material underneath railways, for

6:49

instance, to restore last elevation. Bolstering.

6:53

Subways though could be much more challenging.

6:55

We. Don't have a concrete solution for that

6:57

says. Here's a. In. Most cases,

6:59

when that happens, it just results in

7:02

shutting down the project and trying to

7:04

open a new lane. This.

7:06

Isn't just Mexico City's problem? Earlier

7:08

this year, Sears A. and his

7:10

colleagues found that the east coast

7:12

infrastructure is in serious trouble due

7:14

to slower yet steady subsidence. They.

7:17

Calculated that twenty nine thousand square miles

7:19

of the Atlantic Coast are exposed to

7:21

sinking of up to zero point zero

7:23

eight inches a year. Affecting.

7:25

Up to fourteen million people and

7:27

six million properties. Some. Fourteen

7:30

hundred square miles are thinking up to point

7:32

two inches a year. Differential.

7:34

Subsidence is not only threatening railways

7:36

the researchers found, but all kinds

7:38

of other critical infrastructure like levees

7:41

in airports, A. Metropolis The

7:43

like New York City has the added

7:45

problem of sheer weight pushing down on

7:47

the grounds, which alone leads to subsidence.

7:50

The. Bay Area to is sinking on either

7:52

coast. Subsidence is greatly exacerbating the problem.

7:54

As sea level rise the land is

7:57

going down just as the water is

7:59

coming up. Wherever. In

8:01

the world is happening, people have to

8:03

stop over extracting groundwater to slow subsidence.

8:06

New. Systems are already relieving pressure

8:08

on Oct refers it's getting cheaper and

8:10

cheaper to recycle toilet water into drinking

8:12

water. for instance, And. More cities

8:15

are deploying sponge infrastructure. lots of

8:17

green spaces that allow rainwater to

8:19

soak into the underlying awful for

8:21

essentially reinflate in the land to

8:23

fend off subsidence. Such.

8:25

Efforts are increasingly urgent as climate

8:28

change exacerbates droughts in many parts

8:30

of the world, including Mexico City,

8:32

putting ever more pressure on ground

8:34

water supplies. With. Increasing

8:36

satellite data cities can get a better

8:39

handle on the subsidence. They can't immediately

8:41

avoid. I really feel like governments

8:43

have a chance to use these kinds of studies

8:45

to have a more structured plan of action. Says

8:47

Salon Auto has. Thanks.

8:50

For listening to Wired. My. Name is

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