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LACMA (the Los Angeles County Museum of Art) is built right next to the famous La Brea Tar Pits and that keeps me up at night†.

Question: What is the subsurface structure like adjacent to the Lake Pit? I'm wondering if the LA County Museum of Art and other buildings near the Lake Pit could actually fall in some day. Is the museum built on bedrock and the tar pit next to it is just a small hole in it, or if "the big one" comes (major earthquake) could soil shift and the art museum end up submersed in tar?

†no it doesn't, drinking too much coffee keeps me up at night.

Google Maps of La Brea Tar Pit and LACMA

Google Maps of La Brea Tar Pit and LACMA

Ground truth: LA/Hollywood, so plastic dinosaur...

Google Maps of La Brea Tar Pit and LACMA

Google Maps of La Brea Tar Pit

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    $\begingroup$ The real question is: could the museum be propelled into Trinidad asphalt lake by an asteroid (and fossilize once there)? $\endgroup$
    – Jean-Marie Prival
    Commented Mar 5, 2020 at 8:43
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    $\begingroup$ NOT dinosaur, mammoth (or perhaps mastodon). And to answer the question, we'd have to know a lot more about the subsurface geology of the area - or even the elevations: are the museum buildings significantly upslope from the tar pits? We'd also have to know about the seismic engineering that went into the buildings' designs. $\endgroup$
    – jamesqf
    Commented Mar 6, 2020 at 5:09
  • $\begingroup$ @jamesqf I thought those were brontosauri, no? ;-) So with "Is the museum built on bedrock and the tar pit next to it is just a small hole in it, or..." I'm asking for precisely "the subsurface geology of the area". Since this has been such a geologically interesting area I'm sure this has been studied, examined and written about extensively, I just don't know where to begin to read up on it. $\endgroup$
    – uhoh
    Commented Mar 6, 2020 at 10:06
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    $\begingroup$ Chart of strata formations at La Brea Pots $\endgroup$
    – Keith McClary
    Commented Jan 24, 2021 at 22:27
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    $\begingroup$ In the description it says "recent alluvium (10000-25000 years ago)" I'm not sure what "alluvium" means exactly. $\endgroup$
    – Keith McClary
    Commented Jan 27, 2021 at 23:24

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The two geological faults that may be responsible of large earthquake in proximity of the museum are:

  • Hollywood fault;
  • Santa Monica fault (actually many branches, but they all go together as Santa Monica fault).

The museum seems to be enough far away from the fault trace (the surface expression of the fault itself), so it is unlikely that there will be a major shift in the soil.

However, the museum may sink in the soil due to the earthquake mobilizing the soil, especially if composed of loose sand.

The phenomena responsible of the museum "falling in the soil during an earthquake" is liquefaction. The geological service of California provides you an interactive map to check if a certain address may be under liquefaction hazard https://www.americangeosciences.org/critical-issues/maps/interactive-map-california-earthquake-hazard-zones and ...

at the moment the interactive map is not accesible to me. Sorry :)

If liquefaction is possible, either the tar may quickly move and sputter on/in the museum, or the museum may sink in and later tar may infiltrate slowly in the building.

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  • $\begingroup$ Thank's for your answer! I was hoping that the museum was built on bedrock and the tar pit was just a hole in that rock providing access to oil (tar) trapped in layers below. But it's just soil and not rock? I wish there were a diagram with a cross-section of this kind of tar pit that shows what keeps the soil and tar from just eventually mixing together. I'd always thought that it was rock. $\endgroup$
    – uhoh
    Commented Mar 5, 2020 at 20:23
  • $\begingroup$ @uhoh providing cross section in urban environment is very complicated. Check the app from the californian geological survey, if the museum is on a "possible liquefaction area" then it means it is very likely to stand on a sandy/soil basement. Which I expect to be the case, since reading from here: tarpits.org/research-collections/tar-pits-our-research/geology "the Santa Monica Mountains uplifted and rivers flowing down brought large amounts of sands and gravels that subsequently buried the remains of plants and animals trapped on the surface of the asphalt seeps at Rancho La Brea" $\endgroup$
    – EarlGrey
    Commented Mar 6, 2020 at 9:58
  • $\begingroup$ This area was studied long before it was built up 1 2 due to both it's economic and scientific interest, so I'm hoping that there might be more understood about the subsurface structure here. $\endgroup$
    – uhoh
    Commented Mar 6, 2020 at 10:12
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    $\begingroup$ Don't confuse exploited with studied ... if the target was oil, then they were looking for oil and whatever in between the surface and the reservoir was just "tough or tougher" material to be drilled. Said this just a couple of drlling/mud logs from the wells perforated there would help a lot to get your answer. $\endgroup$
    – EarlGrey
    Commented Mar 6, 2020 at 11:03

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