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Citation: Bradley, K., Hubbard, J., 2025. Several large earthquakes strike northwestern Venezuela. Earthquake Insights, https://doi.org/10.62481/8c943b8f
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On September 24 at 6:21 PM local time, a magnitude 6.2 earthquake struck at a shallow depth beneath a hilly region of northwest Venezuela, east of Lake Maracaibo. Over the ensuing hours, three more large earthquakes have struck, including a M6.3, a M5.8, a M4.9, and a M4.5. Because the two largest earthquakes are very close in size, we can refer to them as a doublet.
Shaking in all three of the largest events was felt across both northwestern Venezuela and northern Colombia.
Without seismometers in the epicentral region, it is pretty tricky to see differences in shaking near the earthquake. The nearest seismometer reported by the USGS is located nearly 300 kilometers away, in Aruba, and recorded intensity II in both events. In general, although the M6.3 was about 50% more powerful than the M6.2, the felt reports look pretty similar, although reports within 50 kilometers of the hypocenters are very sparse. Felt reports can also be sensitive to location and time of day. The first earthquake occurred during the day, when people might have been indoors or outdoors, sitting, standing, or walking. The second earthquake occurred at night; presumably most people were lying down, perhaps sleeping.
News about the earthquake impacts is limited. People about 70 kilometers or more away from the epicenters describe objects moving on shelves and windows shattering. Footage on social media shows fallen bookshelves and shops with the floor littered with merchandise. The highest intensities reported to the USGS Did-You-Feel-It system would be consistent with building damage, but we have not seen any reports of such damage or impacts. If you have any more information on the impacts of these earthquakes, please let us know in the comments.
Tectonic setting
The earthquakes all occurred within the Coro region of Venezuela, a semi-mountainous area northeast of the Mérida Andes mountain range. The western part of the Coro region hosts the north-south running ridges of the Siruma Range; this is where the earthquakes occurred — just east of Lake Maracaibo, a brackish water body that has, over geological history, alternated between fresh and salt water as sea level rose and fell. (It is also famous for its spectacular lightning displays, which put on a show almost every other night, on average.)
The earthquakes in the sequence were all shallow thrust-type events, caused by east-west compression of the uppermost crust. This is, to first order, consistent with the north-south trending ridges that characterize the Siruma range. However, as we will see there was little reason to expect such significant thrust earthquakes here, based on the historical record.
This whole region — from the various branches of the Andes northward to the coast, and beyond — is intensely seismically active. To learn more, check out our previous posts about earthquakes in Colombia and Venezuela.
Put simply, northern Venezuela straddles the complex boundary between the Caribbean and South American Plates. The mountains in this region mark a wide boundary zone between these plates, within which the upper crust has strongly deformed over millions of years. Today, these mountains are crossed by a complex network of faults, many of which are active.
The fault map of northern Venezuela is impressively complicated. Below, we show a modified excerpt from a larger map by Audemard M. (2003). As a side note, our rapid reading of the literature highlights Professor Franck A. Audemard Mennessier as an outstanding proponent of active tectonics research in Venezuela for decades, and we would like to express our appreciation for that great effort that guides our ideas here.
On the map, there are large crustal faults of each type (right-lateral strike slip, left-lateral strike slip, reverse (thrust), and normal) — plus a huge, most seismically quiet megathrust fault lurking below the Caribbean Sea. The basic context is that the Caribbean Plate is trying to slide westward past South America, but is caught up in a complicated sideways collision. The ‘plate boundary’, if it can be called that, is really a wide zone of complex faulting.
Lake Maracaibo is basically encircled (entriangulated?) by three large strike-slip fault systems. To the north, the Oca–Ancón Fault system cuts through the coastal ranges. To the south, the Boconó Fault forms the core structure of the Mérida Andes mountain chain. To the west is the left-lateral Bucaramanga–Santa Marta Fault. The 2025 earthquake sequence occurred right smack in the middle of this tectonic jumble.
It is hard to overstate how unusual this earthquake sequence is for Venezuela. Here is a map of all thrust type earthquakes that were sitting in our focal mechanism database prior to yesterday:
As you can see, there are a few thrust events on each side of the Mérida Andes, and an event or two farther north. However, there are no recorded thrust events around Lake Maracaibo.
For comparison, here is a map of the strike-slip events:
There have been many strike-slip events distributed across the hilly region east of Lake Maracaibo. Based only on the instrumental record, we would have expected that today’s events would be strike-slip, given their location.
Since we don’t have a lot of seismic context to work with, we will just have to look at the geology and speculate about the possible causative faults.
The USGS map below shows faults that were mapped using studies of the geology and the record of long-term deformation of the crust preserved in rocks. This map shows a number of thrust faults (black lines with teeth), including near today’s earthquake (green star). This gives us a clue: we need to look at the local geology to understand what is happening.
Fortunately, people have already worked on the fault structure of the region, although details from the epicentral area itself are pretty thin. We can get a broad sense of possibility from these prior results.
Complex structural geology of the Mérida Andes
The block model below shows a schematic cross-section of the Mérida Andes, constructed using seismic reflection images, geological mapping of rocks at the surface, and seismicity. The area of the recent earthquakes is at the top left, just past Lake Maracaibo.
The basic idea is that the Mérida Andes have been built up by deep shortening of the crust, which has resulted in stacking up of shallower crustal slices above. The mountains have been raised up by slip on many small thrust faults that branch upward from very shallowly dipping thrusts called décollements. At the western and eastern edges of the mountains, there are complicated wedge structures where the upper 10 kilometer sediment package is being peeled off of its basement, folded, and heaved upward.
If we took the figure above and squeezed it horizontally, we could watch the mountain range grow taller and see the shallow thrusts slip. We wouldn’t be able to see the slip on the deep, low-angle thrusts; they never come to the surface. Near the edges of the mountains, we would also see strata tilt upward above the wedge structures.
How do we know that these kinds of strange structures really exist? Well, they have actually been mapped out in this very region using structural geology and in some cases seismic reflection profiles. In particular, these structures are well documented along the western side of the Mérida Andes, not too far from the epicentral area of the recent earthquakes. The buried tips of the biggest fore-thrust faults (blue lines in the figure below) tend to lie beneath the mountain range front. Note that here, the cross sections show a mix of thrust faults dipping to the southeast that cut across the bedding but die out before they reach the surface (blue), and thrust faults dipping to the northwest that run parallel to the tilted bedding (green).
Geologists draw these kinds of faults on cross-sections mostly because they help them solve a geometric puzzle. On the cross-sections above, the sediments on the right have raised up relative to those on the left, but they were certainly deposited at similar elevations long ago. The tilting we see must be due to slip on a thrust fault that is pushing the uplifted sediments upward and towards the left. However, the thrust fault never daylights! How can we lift up rocks at the surface without breaking the surface with faults?
One option is that the slip turns around and comes back on a backthrust, forming a wedge that essentially “peels” the upper layers of rock off of the bottom ones. The benefit of this option is that it can explain a wide zone of constant dip. (Note that the zone of constant dip can also be explained by bending of the underlying fault, which doesn’t require a wedge… but let’s just ignore that).
Option two is that the slip is distributed onto various faults that terminate inside the sedimentary column, turning fault slip into a broader zone of deformation and folding (fault propagation folding). These, too, cannot be seen directly at the surface, because they never break it. Faults like this have been traditionally called “blind,” but we prefer the term “concealed.” The figure below shows some possible configurations for this kind of fault system.
Hunting for the faults that slipped
With these pictures in mind, let’s look back at the epicentral area and see if we can’t puzzle out a candidate fault system for the thrusts. First, we took a quick look at the topography to map out the the tilt of sedimentary layers. Because we don’t have good geological maps for this region, we just inferred those tilts from the triangle-shaped ridges (flatirons) seen in satellite imagery. (If you took a class on structural geology, you may faintly recall that when a surface is tilted and eroded, the “V” in the valleys points toward the dip direction.
We can put those dip directions on a map — the longer line shows the strike direction, i.e. the azimuth of a horizontal on the bedding plane, and the central tick shows which side of the bedding plane dips down. This is Geology 101, which is (unfortunately) a college-level course that the vast majority of people never take, but is really fun. On the following map, we also drew in the already known faults in the region. The dashed-and-queried line is our candidate fault that we will discuss below.
The recent thrust earthquakes lie between two already mapped fault systems. To the east of the earthquakes, the north-south Valera Fault is a left-lateral strike-slip structure that has hosted significant earthquakes. This is probably a vertical structure, and it is not a candidate for our thrust events.
To the west of the earthquakes is the well-known Mene Grande oil field, one of Venezuela’s first great oil producing regions, and where oil and tar seep to the surface in great quantities. The oil field itself is related to a large anticline, which at the surface is associated with a small fault called the Mene Grande Fault. (The anticline is marked by strike-and-dip symbols with ticks that point away from each other.) Since the Mene Grande Fault dips to the west, away from the recent earthquakes, it also is not a candidate fault. (The teeth on the fault mark the dip direction.)
Between the Valera and the Mene Grande Faults, the mountain range front exposes a panel west-dipping sedimentary rocks, reminiscent of the northwest dipping sections at the front of the nearby Mérida Andes.
We speculate that the structure here probably mimics (or is a continuation of) the western Mérida Andes. The zone of west-dipping rocks might mark a wedge structure below, formed above the active tip of a décollement fault lying beneath the mountain range. Slip on thrust faults rising from that décollement produced the structures we see at the surface, including the folds related to the Mene Grande oil field. However, we won’t yet conjecture whether the ruptured faults represent fore-thrusts, back-thrusts, or a combination of both. It is possible that upcoming InSAR measurements of the surface displacement will give us a better estimate of the likely fault geometry.
Our analysis is quick, dirty, and possibly wrong. It seems likely that the structure here has actually been worked out long ago by oil geologists, but we can find very little information in the accessible literature. We are also extremely curious about any effects the earthquake might have had on the oil field. If any of our readers know more about the specific geology of this area, have a different idea about the source faults, or can otherwise correct some part of our rapid analysis, please leave a comment!
References
Audemard, F.A., Machette, M., Cox, J.W., Dart, R. L., Haller, K., 2000. Map and database of Quaternary faults in Venezuela and its offshore regions, U.S. Geological Survey Open-File Report 2000-18, https://doi.org/10.3133/ofr0018
Audemard M, F.A., 2003. Geomorphic and geologic evidence of ongoing uplift and deformation in the Mérida Andes, Venezuela. Quaternary International, 101, pp.43-65. https://doi.org/10.1016/S0040-1951(01)00218-9
Shaw, J.H., Connors, C. and Suppe, J., 2005. Seismic interpretation of contractional fault-related folds. American Association of Petroleum Geologists. https://doi.org/10.1306/St531003
Monod, B., Dhont, D. and Hervouët, Y., 2010. Orogenic float of the Venezuelan Andes. Tectonophysics, 490(1-2), pp.123-135. https://doi.org/10.1016/j.tecto.2010.04.036
There is no surprise of having thrust earthquakes in western Venezuela, outside of the Andes foothills. And on N-S faults, since it fits the regional stress tensor, which shows an E-W trending max horizontal stress west of the Cordillera de los Andes (for more details, refer to Audemard et al., 2005; Earth Science Reviews). Have a look to the compilation Map of Quaternary faults of Venezuela and adjacent regions and its pamphlet published by the USGS as an open-file report (USGS OFR 00-0018), which displays several active N-S faults affecting the Lake Maracaibo basin.
Dear Kyle Bradley,
I would like to sincerely congratulate you on your extensive and rigorous report on the earthquake that struck Venezuela in … September 2025. I find it especially valuable that you drew upon the expertise of Dr. Franck Audemard, a Venezuelan geologist of internationally recognized prestige in tectonics, seismotectonics, and geological risk. The support of an academic authority of his caliber gives your work even greater professional and scientific solidity.
I had the honor of being one of Dr. Audemard’s students during my doctoral studies at the Central University of Venezuela, in the course Faults and Faulting. I still keep both my notes and the invaluable lessons he imparted with exceptional academic rigor, which remain to this day a reference for my formation and professional practice as a civil engineer.
For this reason, my congratulations are twofold: first, for the quality and depth of your publication —which I follow with great interest— and second, for grounding it in the knowledge of someone who is, without a doubt, the foremost authority in Venezuela in the field of structural geology and seismotectonics.