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Dr. Judith Hubbard Profile picture
@JudithGeology
Jan 15, 2022 • 3 tweets • 4 min read • Read on X
A #volcano just erupted near #Tonga - but why was it there in the first place?

Tonga sits on top of the #TongaKermadec #subductionzone, where the #PacificPlate sinks below the #AustralianPlate.

The subducting #PacificPlate carries the culprit into the mantle: #water. 🧵1/3 Source: https://source.wust...
Some people think that volcanoes at subduction zones are due to frictional heating from the two plates rubbing against each other - NO!

In this case, melting is because of the addition of water, sort of like how adding salt can make ice melt. 2/3

Is this the only volcano in the region? Absolutely not. Volcanoes parallel the plate boundary, a string of conical mountains 2000 m high, occasionally poking above the sea. Usually quiet, but built over millions of years through thousands of eruptions. 3/3

#tectoplot Image

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More from @JudithGeology

Dr. Judith Hubbard Profile picture
Oct 17, 2023
BSSA just published a paper where the authors claim to predict earthquakes days in advance, using AI. A quick read-through raises many question.

Does anybody know about this study and why BSSA is publishing AI/earthquake prediction papers now?

1/
doi.org/10.1785/012023…
Although the paper is framed around "earthquake forecasting," it's a prediction paper. They use the word prediction in both the paper and the supplement.

2/
This was reviewed through BSSA, and is being promoted by SSA.
Earthquake prediction, if it were proved, would be a BIG DEAL. The bar for passing review should be very high.

3/
Read 5 tweets
Dr. Judith Hubbard Profile picture
Mar 29, 2023
Today's M4.7 earthquake in Italy likely occurred on an east-west strike-slip fault that previously produced a pair of ~M5.8 earthquakes in 2002.

The 2002 earthquakes were horrible; fortunately today's event was much smaller.

1/
earthquake.usgs.gov/earthquakes/ev…
The 2002 Molise earthquakes occurred within ~1 day of each other (Oct 31 and Nov 1). The first quake collapsed a school, killing half the children inside (26 of 51). At the time, the area was considered to have no seismic hazard.

2/
en.wikipedia.org/wiki/2002_Moli…
The school was built with reinforced concrete, but the second floor was added later, and it is possible that this made the building more susceptible to collapse.

3/
Read 9 tweets
Dr. Judith Hubbard Profile picture
Mar 28, 2023
Several people have asked me recently about whether we should expect a large earthquake on the Afrin fault, south of the Feb 6 rupture.

First: no one can predict earthquakes, so if anyone has told you they can, they are wrong.

But let's take a look anyway.

1/
First, what is the Afrin fault? The AFEAD dataset has a small fault listed under this name, running through the city of Kilis, Turkey. An extension of this fault is mapped near the city of Afrin, Syria.

These faults are part of the northern end of the Dead Sea Fault.

2/
You can explore these faults yourself. The dataset describes the "Afrin fault" as having a slip rate of <1 mm/yr - i.e., not really detectable. But the extensions are a bit faster, maybe up to 5 mm/yr. The Dead Sea Fault slips ~5 mm/yr.

3/
neotec.ginras.ru/index/mapbox/d…
Read 14 tweets
Dr. Judith Hubbard Profile picture
Mar 28, 2023
Why did a M5 earthquake occur HERE yesterday, in what is apparently the middle of the African Plate?

Answer: It's not the middle of the African Plate, it's the East African Rift: the continent is pulling apart at a rate of ~1-5 mm/yr.

1/
Yesterday's earthquake was just the latest in a long series of earthquakes - and not the largest, either; there was a M6 in 2020 to the south.

The "rift" isn't a single fault, but many.

2/
Volcanoes are scattered along the rift, too. As the crust thins, deeper areas experience lower stress, allowing "decompression melting" - hot rocks kept in a solid state by pressure will melt if that pressure is released.

3/
nature.com/articles/s4146…
Read 8 tweets
Dr. Judith Hubbard Profile picture
Mar 28, 2023
A M6 earthquake occurred a few hours ago offshore Japan. Due to its magnitude & distance from shore, it was not damaging, but the setting is interesting to explore.

1/
This is a subduction zone: the Pacific Plate is subducting below the Okhotsk Plate at a rate of ~9 cm/yr. The Okhotsk Plate used to be considered part of the North American Plate (even though it's in Japan!) but it actually moves slightly differently.

2/
en.wikipedia.org/wiki/Okhotsk_P…
This is a very active place, seismically speaking. Today's earthquake occurred on the subduction interface fault (called a "megathrust" - i.e. a really big thrust fault). That megathrust has hosted many large earthquakes, including...

3/
Read 17 tweets
Dr. Judith Hubbard Profile picture
Mar 27, 2023
A lot of earthquakes have one large event followed by aftershocks.

But sometimes, we see something like this instead: a set of several similar-magnitude events (with additional small seismicity).

That's what has been happening near Kayseri, Turkey.

1/
It started on Feb. 23, with a M3.8. Then, a few days later, a little microseismicity.

Then, suddenly, a M4.6 on Feb. 28.

(EMSC reports it as an mb4.4, which here is converted to Mw4.6 - different ways of measuring magnitude.)

2/
People in the area, already spooked by the Feb. 6 Turkey-Syria events to the SE (which were felt here), reported shaking of intensity 4-5.

That's similar to what they felt on Feb. 6 - even though the earthquake was much smaller, it was much closer.

3/
Read 12 tweets

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