For residents along the Pacific Rim and the Hawaiian Islands, recent months have brought a flurry of seismic activity and heightened scientific scrutiny. From the deep tremors beneath Hawaii’s volcanic giants to the mounting stress along California’s infamous San Andreas and San Jacinto faults, the ground beneath millions of feet seems anything but still. But what’s really happening below the surface—and how worried should people be?
On May 22, 2026, the Island of Hawaiʻi was jolted by a magnitude-6.0 earthquake, its epicenter southeast of Captain Cook and plunging 14 miles (23 km) below the ocean surface, according to the US Geological Survey Hawaiian Volcano Observatory (HVO). The event was widely felt, rattling nerves and reminding locals of the islands’ geologic dynamism. It wasn’t an isolated incident. Just days later, on June 2, a magnitude-4.6 quake struck northwest of Keauhou at a depth of 21 miles (24 km), followed by a magnitude-4.7 event east of Pepeʻekeo on June 9, this one even deeper at 24 miles (39 km). Smaller, yet notable, quakes continued into July, including a magnitude-3.3 southeast of Pāhala and a magnitude-3.2 north of Wai‘ōhinu.
But here’s the twist: these deep Hawaiian earthquakes aren’t directly tied to the islands’ famous magmatic fireworks. Instead, as HVO scientists explained in their weekly Volcano Watch column, these are mostly “flexure events,” caused by the immense weight of the Hawaiian Island Chain pressing down on the oceanic lithosphere. Imagine dropping a bowling ball onto a mattress—the weight creates a sag, and the surrounding material bends and folds. In Hawaii’s case, the lithosphere, though relatively cool and brittle, can only bend so far before strain is released as an earthquake. These flexure events, while less common than volcanic quakes, are often felt more widely because their seismic waves travel efficiently through the dense lithosphere.
This flexing is a direct consequence of Hawaii’s unique geology. Unlike California, Japan, or Indonesia—regions that sit atop the world’s tectonic plate boundaries and experience frequent seismic fireworks—Hawaii is perched in the middle of the Pacific Plate, far from any boundary. Its volcanism is driven by a mantle plume, or “hot spot,” a deep column of hot rock that has punched through the plate to build the islands over millions of years. As the islands grow heavier, the lithosphere sags, sometimes releasing energy in the form of deep earthquakes. These are distinct from the more common, shallower quakes caused by magma movement or faulting within the islands themselves.
Yet, not all deep quakes in Hawaii are flexure events. The Pāhala seismic swarm, for example, regularly produces quakes larger than magnitude-4 at depths greater than 18 miles (30 km) off the island’s southeast coast, believed to be linked to magma transport rather than lithospheric flexure. Regardless of the cause, HVO urges residents to always “drop, cover, and hold on” during shaking and to be mindful of tsunami risks.
Meanwhile, California’s seismic story is taking a dramatic turn of its own. On July 5, 2026, the New York Post splashed a headline: “LA on earthquake alert as fault lines hit highest stress levels in history.” While the tabloid’s tone may have been breathless, the underlying science comes from a robust new study published in the Journal of Geophysical Research by Liliane Burkhard and colleagues at the University of Bern.
Their research zeroes in on the southern San Andreas fault system, particularly the complex interplay between the San Andreas and the parallel San Jacinto fault. Using a mix of paleoseismic trench data, slip rates, and stress modeling, the team reconstructed the stress evolution of these faults over the past 900 years. Their findings? The three fault segments at Cajon Pass—a critical juncture in San Bernardino County—are now at or near their highest stress levels since at least 1100 AD.
The northern San Andreas segment (dubbed MOS) has surpassed its pre-1856 rupture stress, the San Jacinto segment (SJB) is likewise at a 900-year peak, and the southern San Andreas (NSB!) is at its second-highest value. This matters because Cajon Pass acts as an “earthquake gateway,” sometimes allowing ruptures to leap from one fault to another, resulting in much larger earthquakes than either fault could produce alone. In 1857, for example, a magnitude-7.9 quake ruptured 225 miles of the San Andreas but stopped at Cajon Pass. In 1812, the gateway was “open,” allowing a rupture to propagate along both faults.
“Given the elapsed time since these faults have ruptured, the probability of an earthquake in the near future is high,” the authors write, while cautioning that this is not a prediction of imminent disaster. Earthquake science, after all, is fraught with uncertainty. Faults are not uniform; they are riddled with “asperities”—strong patches that can lock a fault together until enough strain builds to break them. The precise timing and magnitude of the next big quake remain unknowable, but the accumulating stress is a clear warning flag.
The implications for Southern California are sobering. Both the San Andreas and San Jacinto faults have been eerily quiet for over a century, despite being responsible for some of the largest quakes in the region’s history. The study’s modeling suggests that the “earthquake gateway” at Cajon Pass is currently open, raising the possibility of an extended rupture involving all three fault segments—an event that could have far-reaching consequences for Los Angeles and beyond.
Of course, modeling has its limitations. The authors acknowledge uncertainties in estimating earthquake magnitudes from ancient trench data, and their models make simplifications about fault materials and ignore the influence of other regional faults. Still, the consensus among seismologists is that the long seismic lull in Southern California has only increased the region’s vulnerability.
Back in Hawaii, volcanic activity continues apace. Kīlauea has been erupting episodically within its summit caldera since December 2024, with its USGS Volcano Alert level at ADVISORY. Episode 50 of summit lava fountaining lasted seven hours on June 27, and models indicate that episode 51 is most likely to occur between July 11 and 15. Maunaloa, on the other hand, remains quiet, its alert level at NORMAL.
For residents and policymakers in both Hawaii and California, the message is clear: the earth’s restless energy is ever-present, and preparedness is not just prudent—it’s essential. Whether it’s the slow sagging of the Pacific Plate beneath volcanic islands or the invisible buildup of tectonic stress along fault lines, the next big shake is always a possibility. Staying informed and ready is the best defense against nature’s unpredictable power.