Significant Earthquakes and Faults
Chronological Earthquake Index
Galway Lake Earthquake
Type of Faulting: right-lateral strike-slip
Time: May 31, 1975 / 6:39 pm PDT
Location: 34° 31' N, 116° 29.3' W 58 km (36 miles) southeast of Barstow
Magnitude: ML5.0 (estimated)
Depth: 5.8 km
Surface Rupture Length: 6.8 km
Fault Ruptured: Galway Lake Fault
Maximum Surface Displacement: 1.5 cm
Essentially a minor earthquake that caused very little damage (due to its remote location and its relatively moderate magnitude), the Galway Lake earthquake of 1975 was significant because it was only the second historically recorded earthquake to cause surface rupture within the Mojave block -- an area defined by the Garlock fault to the north and northwest, and the San Andreas fault to the south and southwest -- the first being the Manix Earthquake of 1947. The Galway Lake earthquake also was of note because the fault ruptured was previously unmapped. Upon further studies, it was discovered that the Galway Lake fault (named for nearby Galway Lake, a desert playa just east of the fault) had, indeed, ruptured before, though possibly not for hundreds, or even thousands, of years.
Since then, of course, we have seen fault rupture in the Mojave block far in excess of both the Manix and Galway Lake events -- that of the Landers earthquake of 1992. But, at the time, the Galway Lake rupture, though small, was something of a novelty, and of great interest. Taking the Landers earthquake into consideration, though, it is interesting to note that the Galway Lake fault appears to be an off-shoot of the Emerson fault, one of the faults that ruptured in the Landers quake. Six months after the Galway Lake rupture, the Goat Mountain earthquakes (two magnitude 4.7 quakes) occurred just southeast of Galway Lake, and four years later, the Homestead Valley earthquakes (magnitudes 4.9, 5.3, 4.5, and 4.8) occurred, also in the vicinity of the future Landers rupture. All these quakes would have altered the seismic stress in the area, and may thus have been instrumental in "setting up" the eventual Landers rupture.