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Site response in Cali, Colombia and its effects on building collapse during the M7.4 Colombia earthquake on august 10, 2026

Bayron Salazar

Civil Engineer, PhD Student

Universidad del Valle

(G-7) Grupo de Investigación en Ingenierías Sísmica, Eólica, Geotécnica y Estructural

eicg.univalle.edu.co/G-7

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Holocene volcanoes

Pleistocene volcanoes

Intraslab events epicenters

Destructive intraslab events

Subduction zone

Collision zone

Other

Epicenters of intraslab events are close to south-western cities

Over the past 100 years, ten intraslab events in western Colombia have reached intensities greater than VII on the EMS-98 scale

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Timeline of Colombian codes

1984

CCCSR-84

1998

NSR-98

2010

NSR-10

2014

Cali microzonation

3 soil categories according to thickness of stable deposits of sands, gravels, or hard clays

4 soil categories according to VS30 and thickness of stable deposits of sands, gravels, or hard clays

6 soil categories according to VS30, SPT and Su tests and thickness of soft clays deposits

10 zones based on Site-specific geotechnical investigations

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Site	Seismic Zone	PGA_EW [g]	PGA_NS [g]
RAC03	Zone 3	0.29	0.29
NOVA	Zone 4D	0.10	0.10
IMBA	Zone 4C	0.19	0.19
SOLEV	Zone 1	0.03	0.04
JARC	Zone 4D	0.07	0.10
CLOCC	Zone 4A	0.12	0.10
COALA	Zone 6	0.17	0.16

72 % of total collapses in Cali during ground-shaking ocurred within zone 4C

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Zone 4C is characterized by the presence of clayey and silty soils with interlayered strata of organic material and average fundamental periods of 1.8 s.

Ana Pilar Building. https://shorturl.at/xCH1a

(G-7) Grupo de Investigación en Ingenierías Sísmica, Eólica, Geotécnica y Estructural

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Pseudo-acceleration response spectra with 5% damping, compared with code-based spectra and the corresponding spectrum from the Seismic Microzonation of Cali.

max Sa = 0.36 g at 1.14 s

Site period=0.75 – 1.25 s

max Sa = 0.84 g at 0.44 s

Site period=0.75 – 1.25 s

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Site period = 1.5 – 2.0 s

max Sa = 0.73 g at 0.68 s

Site period=0.75 – 1.25 s

max Sa = 0.46 g at 0.82 s

(G-7) Grupo de Investigación en Ingenierías Sísmica, Eólica, Geotécnica y Estructural

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max Sa = 0.82 g at 0.33 s

Site period=1.25 – 2.0 s

Site period=0.75 – 1.25 s

max Sa = 0.36 g at 0.26 s

In general, the maximum Sa values do not always correspond to the characteristic period of the soil

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Site period = 1.5 – 2.0 s

max Sa = 0.73 g at 0.68 s

13 buildings collapsed within seismic zone 4C during ground shaking

46% of collapses with no seismic design code (Before 1984)

54% of collapses with seismic design code after CCCSR-84 (1984) and before NSR-10 (2010)

RC-frame approximate periods [s] (NSR-10) of collapses (0.2 to 0.7 s)

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Site period=0.75 – 1.25 s

max Sa = 0.84 g at 0.44 s

Some collapsed buildings are closer to RAC03 (Zone 3) than to IMBA (Zone 4C)

Larger Sa values within the same range of periods

However, no severe damage was observed in buildings of 1 to 3 stories

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Conclusions:

The seismic microzonation study of Cali should be updated to better understand the seismic behavior of the zones and to better define the boundaries of the zones.

The buildings that collapsed in zone 4C were constructed before the NSR-10 (2010) code and before Cali microzonation (2014).

A seismic network within the city must be established.

The maximum Sa values do not always correspond to the characteristic period of the soil.

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A more comprehensive database would allow for a more detailed examination of the relationships between the observed effects on the buildings, the spectral demand, the characteristic periods of the zones, and the approximate periods of the structures.

Future work:

Expand the inventory by incorporating buildings with varying degrees of damage during the event

The instrumented sites do not fully cover all of Cali’s microzones

Limitations:

The instruments have different installation conditions, including stations in open-field settings and sensors installed at the base or in the basements of buildings, which may involve inherent soil-structure interaction effects.

(G-7) Grupo de Investigación en Ingenierías Sísmica, Eólica, Geotécnica y Estructural

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Prof. Albert Ortiz,

Prof. Alejandro Cruz,

Prof. Eimar Sandoval,

Felipe García,

Danna Forero

DAGMA - Cali

Special thanks:

(G-7) Grupo de Investigación en Ingenierías Sísmica, Eólica, Geotécnica y Estructural

eicg.univalle.edu.co/G-7