Robin Lacassin @RobinLacassin@qoto.org

Two magnitude 6+ event happened in 2018 and 2019 in the very same region than the 3 Februaryb 2024 Mw7.4. The 2018 Mw6.4 #earthquake had a complex (strike-slip + reverse, several fault segments) shallow crustal rupture.
3/n

See: https://doi.org/10.1016/j.epsl.2019.115729 and https://doi.org/10.1785/0220180228

This E-W section at Hualien latitude only shows a 2D view of the complex 3D structure. If the ~20-40km hypocentral depth of the Mw7.4 #earthquake is true*, it's difficult to figure out which fault ruptured. Could be one not reaching upper crustal levels. Just hypotheses.
2/n

Section from Lallemand 2014, https://doi.org/10.1016/j.jseaes.2013.07.043

* Saying "If the ~20-40km depth of the rupture is true" is a big IF as the Taiwan seismic center puts epicenter of the main shock at 15km only. Needs further studies.

Source region of #Taiwan Mw7.4 #earthquake of 6 Feb. has a complicated 3D lithospheric structure: interaction between the Ryuku subduction and accretionary wedge, the accreted Luzon arc (now forming the coastal range), the Philippines plate, and the Taiwan orogenic prism (central range and foothills).
1/n

Reminder: the seminal article about the source of the 464BC #earthquake is this one:

Armijo et al. "A possible normal-fault rupture for the 464BC Sparta earthquake", Nature, 1991, https://doi.org/10.1038/351137a0

Today's reading 👇, some historical papers, with the idea to enrich our teaching in the field next year about the Sparta 464BC #earthquake

A new paper by IPGP and OVPF researchers A. Lavayssière and L. Retailleau:

Capturing #Mayotte’s deep #magmatic plumbing system and its spatiotemporal evolution with #volcano-#tectonic #seismicity

With a beautiful evaluation of #earthquake location uncertainties

https://www.jvolcanica.org/ojs/index.php/volcanica/article/view/219

Today, digging through archives, I found few old papers by Maurice Mattauer – my PhD supervizor looooooong time ago – Paul Tapponnier – with whom I worked for many years here at IPGP – François Proust – One of my teachers when I was an undergraduate – and Jean-Pierre Petit.

I extracted some figures for my #Tectoldies blog.

They are about the High Atlas mountains and Tizi n'Test Fault, site of the Morocco 8 Sept #earthquake and of the ensuing #disaster that claimed thousands of lives.

Have a look to my #Tectoldies blog post:
https://tectoldies.mystrikingly.com/blog/the-tizi-n-test-fault-in-the-high-atlas-of-morocco

#SciArt #tectonics

That song 👇🏽 for #earthquake awareness by Pashupati Sharma & Devi Gharti Magar with the words of Dr. Shiba Subedi from #Seismology at School in #Nepal 🙏🏽👏🏽❤️

Chorus says "Everyone learns how to prepare to survive an earthquake".

"Seismology at School in Nepal" program has been working to make people aware of earthquakes and their better preparation in Nepal.

https://youtu.be/ymE-lrAK0TI?feature=shared

I try to post in French and English about the Turkish #earthquake, here and also on the bird site (where I still reach much more people interested in natural hazards). Also responding to French media…

Not enough time to explain everything in detail though… 😕 Don't hesitate to ask, I'll try to answer whenever possible.

Thoughts for the many victims and injured in Turkey and Syria ❤️

Two faults of the East Anatolian Fault (EAF) system ruptured today. First, a Mw7.8 #earthquake on EAF main strand probably breaking several segments. Second a Mw7.5 to 7.7 on the Sürgü-Çartak Fault (EAF N strand). Both ruptures are outlined by their aftershocks (circles on map), and both are left-lateral.

There are many aftershocks following the two big earthquakes, but the second rupture is rather a triggered earthquake on an adjacent fault belonging to the EAF system.

This reminds us to be wary of possible strong aftershocks or triggered ruptures in the following days-weeks after a big earthquake.

Strong destructive #earthquake in SE Turkey / N Syria, magnitude Mw~7.8.

Mechanism compatible with left-lateral strike-slip on the southern part of East Anatolian Fault system. Aftershock zone extends for ~250km along that fault system. Complex source time function may suggest rupture on several fault branches. The left-lateral East Anatolian Fault system bounds the Anatolian tectonic microplate to the east.

Sources of maps:
• http://geoscope.ipgp.fr/index.php/en/catalog/earthquake-description?seis=us6000jllz
• https://www.emsc-csem.org/Earthquake/earthquake.php?id=1218444#summary
• http://www.koeri.boun.edu.tr/new/en

Magnitude Mw~7 #earthquake north of #Halmahera (#Maluku island, Indonesia) in a complex tectonic setting where several micro-plates interact. Quite large discrepancy btw depth estimates (16-46km), complicated source time function. Mechanism is mainly strike-slip.

Source of maps and MT solutions:
https://emsc-csem.org/Earthquake/earthquake.php?id=1211853#
and
http://geoscope.ipgp.fr/index.php/fr/catalogue/description-d-un-seisme?seis=us7000j553

I am totally astounded by what I read when I compare these two texts: Maria Graham's description of the coastal #uplift due to the 1822 #Valparaiso #earthquake, versus Charles Darwin's text on very similar phenomena related to the 1835 #Concepción earthquake.

Read carefully, paying attention to the expressions used. It's like if #Darwin borrowed Maria Graham's words, but also her interpretation about the accumulation of earthquakes raising the coast on the long term. 🤔
Any comment ?

Both 1822 and 1835 earthquakes happened in Central #Chile on the #subduction #megathrust between Nazca and South America #tectonic_plates. Darwin's description, based on Fitz Roy (Beagle's captain) observations, is considered as seminal.

Thanks @haq for pointing me to the work by Maria Graham.

In my new #tectoldies post I follow up on the 1891 #Japan #earthquake and the seminal article by Bunjiro Kotô published in 1893:

https://tectoldies.mystrikingly.com/blog/the-great-1891-earthquake-in-central-japan-2

In this article, probably for the first time in the world, B. Kotô makes detailed descriptions of the earthquake surface rupture and offsets, and explicitly linked #earthquakes to #tectonic faulting.

Kotô gave a beautiful 3D sketch 👇🏼 and an amazing narrative about mole-tracks (a now commonly used term for some specific surface ruptures): “Amongst the extraordinary things done by the earthquake, one that always drew attention was the earth-rent. It strikes across hills and paddy-fields alike, cutting up the soft earth into enormous clods and raising them above the surface. It resembles the pathway of a gigantic mole more than anything else.”

#mastoart #history #sciencehistory #tectonics

I just revived my #Tectoldies blog, which was a little sleepy for a while, with a new post about the first ever described #earthquake surface rupture (that of the 1891 Nobi Mw~7.5 earthquake in central Japan). 1/n

The 1891 fault rupture was indeed perfectly described and interpreted by Bunjiro Kotô in a 1893 article. It is admirably imaged by a B&W photograph in Kotô's article, and by this delicate anonymous watercolour painting 👇🏼, perhaps the first artist view of an active tectonic fault.

Read more: https://tectoldies.mystrikingly.com/blog/the-great-1891-earthquake-in-central-japan-1

My Tectoldies blog is about “the beauty of tectonics – the art of geological sections & other tectonic sketches.” Feel free to explore and comment previous posts. I'll toot about some of them soon.

#tectonics #ScienceArt #MastoArt #history #Japan #geology

USGS got very similar mechanism, but puts hypocenter deeper (around 20km). This perhaps means that the #earthquake rupture happened in the Gorda tectonic plate beneath the upper N American plate. The small Gorda plate is plunging under N America along the #Cascadia #subduction zone.

Magnitude Mw6.4 #earthquake in the region of the #Mendocino triple junction, at northern end of the San Andreas fault, #California. Mechanism is strike slip; rupture may have occurred on any of the ~N-S or ~E-W fault plane as it's a tectonically complicated area.

Mechanism Geoscope IPGP: http://geoscope.ipgp.fr/index.php/en/catalog/earthquake-description?seis=nc73821036

In 1999 the North Anatolian Fault (NAF), Turkey, broke during two destructive #earthquakes east of Istanbul (Mw7.4 Izmit and Mw7.2 Düzce earthquakes respectively on 17 Aug and 12 Nov).

Today's Mw6.1 #earthquake happened just east of Düzce with a faulting mechanism very similar to the 12 Nov 1999 event (strike-slip with small normal component). Its epicenter is located little to the north of the main NAF fault trace.

Map with MT and source function from #IPGP #Geoscope http://geoscope.ipgp.fr/index.php/fr/catalogue/description-d-un-seisme?seis=us7000irp8

Other map shows in red the fault broken by the two 1999 events (purple and red stars locate epicenters, yellow circles show aftershocks). From C ̧akir et al. GJI 2003 https://doi.org/10.1046/j.1365-246X.2003.02001.x.

Magnitude Mw 7 #earthquake offshore #Guadalcanal island in #Solomon archipelagos. Small #tsunami waves in Honiara on other side of the island.

There, at the San Christobal trench, the Australian plate is subducting beneath the Solomon arc.

Moment tensor solution ("beach ball" on the map) implies rupture either on a vertical fault or a nearly horizontal one. More data and models will be needed to understand if the earthquake happened on the subduction megathrust or within the downgoing plate.

MT and source function from http://geoscope.ipgp.fr/index.php/en/catalog/earthquake-description?seis=us7000irfb
Sea level graph from https://webcritech.jrc.ec.europa.eu/SeaLevelsDb/Device/1695

Today's #earthquake in W Java has a strike-slip mechanism according to moment tensor solution by BMKG, Indonesian Meteorology, Climatology, and Geophysical Agency - https://inatews.bmkg.go.id/

See map 👇🏼 with the "beach ball" showing the fault mechanism with two possible very steep fault planes.

Hypocenter shallow depth ~11km and closeness to Cianjur town (less than 10km), where damages are reported, likely explains its destructive character. Strong shaking also reported in Jakarta at ~80km from the epicenter.