Earthquake in Venezuela: What went wrong with the geology?

When a structure collapses during a seismic event, the answer is rarely found exclusively in the design of the superstructure. Engineers and architects must understand that structural damage is, for the most part, a symptom; the true pathology begins tens of kilometers beneath our feet.

In Venezuela, we cannot afford to design infrastructure ignoring the complex tectonic interaction upon which we are situated. Understanding the threat is the first step to ensuring structural resilience and protecting the lives of all inhabitants of residential and commercial buildings.

Below, we will conduct a forensic analysis of the geological dynamics governing our territory, before even thinking about laying the first beam.

The Tectonic Machine: Kinematics of the San Sebastián Fault

Northern Venezuela is defined by a system of strike-slip faults that absorbs the relative displacement between the Caribbean Plate (moving eastward) and the South American Plate (moving westward). This tectonic triad is composed of the Boconó, San Sebastián, and El Pilar faults. However, the behavior of the San Sebastián Fault is of particular critical interest.

• The Morón Knot: Stress begins to transfer from the Andes through Yaracuy state, reaching a critical inflection point known as the Morón Knot. At this intersection, the fault's kinematics change drastically, accumulating high-density elastic energy.

• Coastal Transit: From Morón, the fault plunges and runs parallel to our central coast, dictating the direct seismic risk over La Guaira state and, by proximity, over the Caracas valley. Dextral (right-lateral) strike-slip friction along this segment is a documented geological time bomb.

• Outflow at Cabo Codera: The main segment of San Sebastián culminates its kinematic journey near Cabo Codera, in Miranda state, where the system transfers its stresses to the El Pilar Fault in the east of the country.

Wave Propagation and Seismic Microzonation in Caracas

The release of energy in the San Sebastián Fault generates shear (S) and compression (P) seismic waves that travel through the crust. But why does an earthquake of the same magnitude affect different areas of the same city so disparately? The answer lies in the underlying geology.

This is where the rigor of Caracas seismic microzonation comes into play. The valley of the Venezuelan capital is a deep and highly heterogeneous sedimentary basin.

• Sediment Depth: In areas such as Los Palos Grandes or Sebucán, Quaternary sediments can exceed 300 meters in depth until soft or hard rock is found.

• Site Effect: When traveling from hard bedrock to these soft sedimentary strata, seismic waves experience a decrease in their propagation velocity, which forces a drastic increase in wave amplitude due to the principle of energy conservation.

• Resonant Frequency: If the natural vibration frequency of the soft soil coincides with the fundamental frequency of the structure it supports, resonance occurs, multiplying lateral displacements until the building collapses.

Ignoring these variables is to contravene the fundamental principles of COVENIN 1756 (Earthquake-Resistant Buildings). Furthermore, in saturated granular soils, this site effect can trigger soil liquefaction, where the ground completely loses its bearing capacity, behaving like a dense fluid.

The Soil Dictates the Rules (Before the First Beam)

Geology provides us with the input data (response spectra, expected maximum accelerations, soil profiles), but structural engineering is responsible for providing the physical response. The soil dictates the rules of the game before the first beam is laid.

When facing the high ductility demands required by areas of high seismic threat (such as Seismic Zones 5 and 6 according to COVENIN), material selection is non-negotiable. We need systems capable of entering the inelastic range without losing their vertical load capacity, dissipating energy through controlled plastic deformations.

This is where structural design in hot-rolled steel demonstrates its superiority. The use of W, IPE, HEB profiles and robust tubular sections (such as heavy conduven) allows us to guarantee prequalified connections and moment-resisting frames (SMF) or concentrically/eccentrically braced frames (SCBF/EBF) that can withstand the demanding drifts imposed by the site effect.

Structural Engineering without Improvisation:

The seismic threat in Venezuela is a geological constant, but structural vulnerability is a variable that engineers and architects can control and reduce to zero. Don't let poor design overshadow the investment in your projects.

The transition from a seismic microzonation study to a safe building requires millimeter precision in the nodes and impeccable detailing. To optimize your workflow and ensure the rigor required by the COVENIN standard and AISC, we invite you to visit Descargaplanos.com.

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