Pacific Plate

References

Images

Map of northern California showing the affected area of the 1989 Loma Prieta earthquake, including San Francisco, Oakland, San Jose, Santa Cruz, and Monterey Bay. Color-coded zones indicate levels of perceived shaking from violent near the epicenter along the San Andreas Fault to moderate further away. The map also marks fault lines, plate boundaries, and the earthquake's epicenter.

World map highlighting the major tectonic plates, each shaded in a different color, with labeled names such as Pacific Plate, North American Plate, Eurasian Plate, African Plate, South American Plate, and Indo-Australian Plate. Arrows across the map indicate the direction of movement for each plate.

Pacific Plate

geology

Written by

The Information Architects of Encyclopaedia Britannica

Last updated

July 1, 2026

Quick Summary

Map of northern California showing the affected area of the 1989 Loma Prieta earthquake, including San Francisco, Oakland, San Jose, Santa Cruz, and Monterey Bay. Color-coded zones indicate levels of perceived shaking from violent near the epicenter along the San Andreas Fault to moderate further away. The map also marks fault lines, plate boundaries, and the earthquake's epicenter. — 1989 San Francisco–Oakland earthquake Map of the 1989 San Francisco–Oakland earthquake (also known as the Loma Prieta earthquake). The quake struck with a moment magnitude of 6.9 on October 17, just before the start of the third game of the World Series, which was being held at San Francisco's Candlestick Park. Sixty-three people died, and nearly 3,800 were injured. The baseball championship between the San Francisco Giants and the Oakland Athletics was suspended for 10 days because both cities suffered significant damage.

The Pacific Plate is a major tectonic plate whose movements are fundamental to understanding the geology of the Pacific region. Along its boundaries, significant geological activity occurs.

In the northeastern Pacific, the Pacific Plate moves laterally alongside the North American Plate along transform faults like the San Andreas Fault. This movement causes considerable seismic activity, making California highly prone to earthquakes.1

To the west of Oregon and Washington, the Pacific Plate is spreading at the Gorda and Juan de Fuca ridges. Here, the Juan de Fuca Plate subducts beneath the North American Plate, fueling the volcanic activity in the Cascade Range.1

In the western Pacific, island arcs and deep trenches mark convergent zones where plates collide and one is subducted. Conversely, the East Pacific Rise is a spreading center where new crust is formed. The Pacific Ocean itself is the largest ocean on Earth, covering about one-third of its surface.234

Summary created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

4 Britannica Sources

Ask Britannica AI about this topic

Britannica doesn't have a full article on this topic, so we've curated a list of our relevant coverage.

ocean basin
Evolution of the ocean basins through plate movements
…with the growth of the Pacific Plate and the consumption by subduction of its bordering plates, including the Izanagi, Farallon, and Phoenix. The Pacific Plate moved northward during this phase and continues to do so today.
Read More
…with the growth of the Pacific Plate and the consumption by subduction of its bordering plates, including the Izanagi, Farallon, and Phoenix. The Pacific Plate moved northward during this phase and continues to do so today.
Read More

Japan earthquake and tsunami of 2011
The earthquake and tsunami
…Eurasian Plate from the subducting Pacific Plate. (Some geologists argue that this portion of the Eurasian Plate is actually a fragment of the North American Plate called the Okhotsk microplate.) A part of the subduction zone measuring approximately 190 miles (300 km) long by 95 miles (150 km) wide lurched…
Read More
…Eurasian Plate from the subducting Pacific Plate. (Some geologists argue that this portion of the Eurasian Plate is actually a fragment of the North American Plate called the Okhotsk microplate.) A part of the subduction zone measuring approximately 190 miles (300 km) long by 95 miles (150 km) wide lurched…
Read More

Papua New Guinea
Relief
…Australian Plate with the westward-moving Pacific Plate. The low-lying plains of southern New Guinea are geologically part of the Australian Plate. Indeed, New Guinea was separated physically from Australia only some 8,000 years ago by the shallow flooding of the Torres Strait. The southern New Guinea plains, called the Fly-Digul…
Read More
…Australian Plate with the westward-moving Pacific Plate. The low-lying plains of southern New Guinea are geologically part of the Australian Plate. Indeed, New Guinea was separated physically from Australia only some 8,000 years ago by the shallow flooding of the Torres Strait. The southern New Guinea plains, called the Fly-Digul…
Read More

Pacific mountain system
Geology
…lateral, northerly movement of the Pacific Plate (west) relative to the North American Plate (east) along transform faults. To the north, in British Columbia, this movement has been along the offshore Queen Charlotte Fault, while in California it has been along the San Andreas Fault. Subduction (crustal sinking) is not…
Read More
…lateral, northerly movement of the Pacific Plate (west) relative to the North American Plate (east) along transform faults. To the north, in British Columbia, this movement has been along the offshore Queen Charlotte Fault, while in California it has been along the San Andreas Fault. Subduction (crustal sinking) is not…
Read More

Earth
The outer shell
…an oceanic plate is the Pacific Plate, which extends from the East Pacific Rise to the deep-sea trenches bordering the western part of the Pacific basin. A continental plate is exemplified by the North American Plate, which includes North America as well as the oceanic crust between it and a…
Read More
…an oceanic plate is the Pacific Plate, which extends from the East Pacific Rise to the deep-sea trenches bordering the western part of the Pacific basin. A continental plate is exemplified by the North American Plate, which includes North America as well as the oceanic crust between it and a…
Read More

Pinnacles National Park
…by tectonic activity as the Pacific Plate has slid along the edge of the North American Plate; a remnant of the formation still exists in its original location, a short distance northeast of Los Angeles. The park also has talus caves that can be explored and is popular with hikers…
Read More
…by tectonic activity as the Pacific Plate has slid along the edge of the North American Plate; a remnant of the formation still exists in its original location, a short distance northeast of Los Angeles. The park also has talus caves that can be explored and is popular with hikers…
Read More

mountain
The North American Cordillera
The very large Pacific Plate, which underlies most of the northern and western Pacific basin, moves north-northwest with respect to North America nearly parallel to the coast, and is subducted beneath southern Alaska and the Aleutians. The volcanic chain that forms the Aleutian Islands and continues into the…
Read More
The very large Pacific Plate, which underlies most of the northern and western Pacific basin, moves north-northwest with respect to North America nearly parallel to the coast, and is subducted beneath southern Alaska and the Aleutians. The volcanic chain that forms the Aleutian Islands and continues into the…
Read More

volcano
Volcanoes related to plate boundaries
For example, the Pacific Plate is bounded by the earthquake zones of New Zealand, New Guinea, the Mariana Islands, Japan, Kamchatka, the Aleutian Islands, western North America, the East Pacific Rise, and the Pacific-Antarctic Ridge.
Read More
For example, the Pacific Plate is bounded by the earthquake zones of New Zealand, New Guinea, the Mariana Islands, Japan, Kamchatka, the Aleutian Islands, western North America, the East Pacific Rise, and the Pacific-Antarctic Ridge.
Read More