Two tiny shakes, barely long enough to blink, nudged western Jalisco awake before sunrise on Friday, October 3. Seismological reports logged a microquake southeast of Puerto Vallarta and another northeast of El Grullo during the night. No alerts sounded; at these magnitudes, they rarely do. But the timing matters. The coast has been busy all week, with a separate 4.1 event off Cihuatlán earlier in the week. We break down what moved, where it happened, and why these Jalisco microquake reports matter even when most people never feel them.
Two micro-earthquakes were recorded in Jalisco during the early hours of Friday, October 3, according to a local report that compiles entries from Mexico’s seismic network. The overnight activity included a tremor logged about 23 kilometers southeast of Puerto Vallarta around 3:33 a.m. local time, and another about 22 kilometers northeast of El Grullo at roughly 1:19 a.m. The Puerto Vallarta event was listed at a magnitude of 3.5 by outlets that mirror the national catalog; both qualify as microquakes on the scale that most residents never feel.
Why a quiet shake matters
Mexico’s Servicio Sismológico Nacional (SSN) maintains the country’s earthquake catalog and publishes rolling updates—entries in this magnitude range are common and typically nondestructive, especially when the epicenter sits offshore or outside dense urban cores. The national “Últimos sismos” board displays frequent low-magnitude events nationwide, illustrating how background seismicity persists even on news-quiet days. That pattern matches Friday’s two Jalisco entries, which did not trigger coastal alerts. In short: microquakes, yes; emergency sirens, no.
The timing coincides with a busy week on the coast. On Wednesday, October 1, a magnitude 4.1 quake was confirmed about 70 kilometers southwest of Cihuatlán—stronger than Friday’s micro events but still modest for the region. It’s a reminder that the Jalisco-Colima margin, where the Rivera and Cocos plates interact with North America, routinely produces light-to-moderate offshore quakes that are felt unevenly along the bay.
What to know about microquakes around the bay
Microseisms—generally magnitudes below about 4—release relatively small amounts of energy. Whether anyone notices depends on several variables, including depth, distance, local soil conditions, and building type. That’s why a 3.5 southeast of Puerto Vallarta in the pre-dawn hours can pass quietly while a similar-sized event on firmer ground near town might feel like a brief jolt. Seismology guides emphasize that magnitude is not the same as intensity, which describes the shaking people and structures experience. For residents, the practical takeaway is simple: maintain routine preparedness, but expect these small entries to come and go without fanfare.
Methodology and verification
We verified Friday’s times and locations against a Jalisco outlet that cites the national catalog and cross-checked the Puerto Vallarta entry with an international live blog that republished SSN data, including the 3.5 magnitude and 03:33 local time. We also reviewed the SSN “Últimos sismos” board to confirm ongoing low-magnitude activity this week and used regional reporting to situate the separate 4.1 Cihuatlán quake on October 1.
