1898 Mare Island earthquake facts for kids
| UTC time | 1898-03-31 07:43 |
|---|---|
| USGS-ANSS | ComCat |
| Local date | March 30, 1898 |
| Local time | 23:43 |
| Magnitude | 5.8–6.4 Mw |
| Epicenter | 38°12′N 122°24′W / 38.2°N 122.4°W |
| Type | Unknown |
| Areas affected | San Francisco Bay Area Northern California United States |
| Total damage | $350,000 |
| Max. intensity | IX (Violent) |
| Tsunami | Possible |
The 1898 Mare Island earthquake was a strong earthquake that shook Northern California. It happened on March 30, 1898, at 11:43 PM local time. The earthquake had a strength, or magnitude, between 5.8 and 6.4. Its shaking intensity, measured by the Mercalli intensity, was between VIII (Severe) and IX (Violent).
People felt the earthquake across a large area. This included most of northern and central California, and even parts of western Nevada. The earthquake caused about $350,000 in damage at the time. This would be about $10.7 million today. The worst damage happened on Mare Island, which is a small piece of land in the northern San Francisco Bay. Buildings there were not very strong, which made the damage worse. Other parts of the San Francisco Bay Area also saw damage, like cracked or partly collapsed buildings. There were also reports of a small tsunami (a large ocean wave) and many smaller shakes called aftershocks. Scientists are still studying exactly what caused this earthquake.
Contents
Understanding Earthquakes: Tectonic Plates
The Earth's outer layer is made of huge pieces called tectonic plates. These plates are always slowly moving. Where these plates meet, there are cracks in the Earth's crust called faults. When the plates slide past each other along these faults, it can cause an earthquake.
California is located on a very active area called the San Andreas Fault system. This system is a network of many faults. They stretch both on land and under the ocean along the coast of California. Near the San Francisco Bay, these faults spread out over about 80 kilometers (50 miles) from east to west.
The 1898 Mare Island Earthquake: What Happened?
The 1898 earthquake was felt over a huge area, about 120,000 square kilometers (46,000 square miles). People felt it from Chico in the north to Monterey in the south. It was even felt as far east as Carson City in Nevada.
Scientists study old earthquakes by looking at how strongly they were felt in different places. They create maps called isoseismal maps. These maps show areas with the same shaking intensity. By comparing the 1898 earthquake's map to maps of more recent earthquakes, scientists can estimate its strength and where it might have started. Early studies suggested the earthquake was a magnitude 6.7. Later, this estimate was changed to 6.4.
Many scientists believe the earthquake happened on one of the faults in the San Andreas Fault system. Some think it was the southern Rodgers Creek Fault. Others suggest the northern Hayward Fault or the southern Green Valley Fault. There were also reports of a small tsunami, which made some scientists wonder if a different type of fault movement caused the quake.
More recent studies have looked at the earthquake again. They found that the severe damage on Mare Island was partly because the buildings there were not built to withstand strong shaking. The earthquake's shaking pattern suggests it might have been close to the Franklin Fault. Even though other faults in the area have caused cracks on the ground, no cracks were seen on the surface after this earthquake.
How Strong Was the Shaking?
Scientists created maps to show how strong the shaking was in different places. One map showed the earthquake's center, or epicenter, north of San Pablo Bay. The strongest shaking, called intensity VIII (Severe), was felt in Vallejo, Mare Island, and much of San Pablo Bay. Some spots even felt intensity IX (Violent).
Even though San Francisco felt strong shaking (intensity VII, Very strong), cities like Santa Cruz and San Jose felt less intense shaking (intensity VI, Strong). Other cities like Ukiah, Stockton, Sacramento, and Gilroy felt moderate shaking (intensity V).
A newer map showed more details about the shaking close to the earthquake's source. It showed that Tubbs Island, northwest of Mare Island, felt very strong shaking (VIII–IX). Schellville, Lakeville, and Mare Island all felt intensity VIII. Many other places, including Santa Rosa, San Rafael, Oakland, and San Francisco, felt strong to very strong shaking (VI–VII). This newer map suggested the earthquake's origin could have been anywhere in a wide area around the southern Rodgers Creek Fault.
Damage Caused by the Earthquake
Even though the earthquake was generally considered moderate, it caused significant damage in some areas. The Mare Island Naval Shipyard was hit hard. Several buildings there partly or completely fell down, and some equipment was broken.
Other places with strong damage included Vallejo and Benicia. In Benicia, a cannery (a factory for canning food) was damaged. In Martinez, the courthouse was damaged. In Sonoma County, places like Schellville and Greenwood Estate also saw severe effects.
In San Francisco, the damage was not as bad. However, one building partly collapsed. A girls' high school also had several thousand dollars worth of damage. In some areas, the soft soil made the damage worse, like at the Whittier School.
Aftershocks: Shaking After the Main Quake
After the main earthquake, many smaller earthquakes, called aftershocks, were felt. Newspapers in the Bay Area reported these aftershocks. They were mostly felt in the areas that experienced the strongest shaking from the main earthquake.
For example, the Sonoma Index-Tribune newspaper reported that in Sonoma, there were four strong aftershocks and more than twenty lighter ones later that night. These lighter shakes mostly just rattled windows. The San Francisco Call newspaper said that the aftershocks were strongest near Tubbs Island. However, they happened more often near Lakeville. Scientists used the information about these aftershocks to help figure out that the main earthquake likely started on the southern Rodgers Creek Fault.
Was There a Tsunami?
Newspapers also reported unusual water disturbances after the earthquake. Sailors in the Pacific Ocean near Point Reyes and the Farallon Islands felt the earthquake. There were also reports of the sea level rising sharply in the San Francisco Bay and on the Napa River.
Scientists who study tsunamis looked into these reports. They know that while the Rodgers Creek Fault mainly causes horizontal movement, some vertical movement is possible. Vertical movement is what usually creates tsunamis. They used a scale from 0 to 4 to decide if a tsunami report was real. A score of 0 meant "not a valid tsunami report," and 4 meant "certainly a valid report." The 1898 event was given a score of 2. This means it was "possibly a valid report," but there wasn't enough clear information or expert observations to be certain.
