Guam Hazard Mitigation Plan - Western States Seismic Policy Council

SECTIONFIVERisk AssessmentTable 5-6 Recent M 5.7 or Greater Earthquakes Felt on Guam, 1975–2010Event Date Description MagnitudeMMIntensity1 Nov 1975 From the same area as the 1936 event. Damage in excess of $1,000,000. No 7.1 VIIIlandslides were noted. This quake was 70 miles deep and was preceded byloud subterranean noises. Many businesses lost stock from shelves, and anumber of structures were damaged; only one injury was reported. Theearthquake was felt strongly in many parts of the island. Epicenter 12.5miles north of the island13 Feb 1983 One person slightly injured at Tamuning. Felt throughout Guam. Epicenter 6.3 Vabout 25 miles north of the island. Minor damage reported in northernGuam.5 Apr 1990 Felt on Guam. Also felt on Saipan. 7.3 IV8 Aug 1993 The most severe examples of ground failure were at the filled area of 7.8 IXCabras (Piti power plant and commercial port) and at the Navy wharfsacross the harbor. Two cases of building failure in the Tumon area werenoted. Old residential units in the Apra Heights housing area sufferednotable damage and were also razed. No bridge failures occurred but theTalofofo, Ylig, and Pago bridges required repairs as well as the utilitiesalong the bridges. Forty-eight people injured on Guam. Extensive damage(IX) to hotels in the Tumon Bay area. Damage (VII) occurred at severallocations in the northern half of the island. One end of the approach to abridge at Pago Bay fell more than 18 inches. Many landslides androckslides were reported, mainly in the southern half of the island. Thepreliminary estimate of loss from damage to commercial buildings is placedat $112 million and loss from damage to private residences is estimated atseveral million dollars.23 Apr 1997 Two separate earthquakes occurred from the fault plane of the August 1993 5.7; 6.3 VIIseries. Four people injured and some damage to buildings on Guam. Felt(VII) at Inarajan, Merizo, and Yona; (VI) in central Guam; (IV) at Dededoand Yigo. A M 5.7 earthquake was followed 5 seconds later by a M 6.3earthquake (not an aftershock). Centered about 27 miles west of Rota.Originated at a depth of 65 miles.12 Oct 2001 Southeast of the initial shock of the August 1993 series. Power was lost. 7.3 VIIThe new school in Piti (on alluvial clay) was most conspicuously affectedas well as schools in the Santa Rita area. One person injured, manybuildings damaged (VII) and utilities disrupted on Guam.26 Apr 2002 Northwest of the August 1993 initial shock. Power was lost through most 7.1 VIIof Guam. At least 5 people slightly injured and some minor damage (VII)to buildings on Guam. Water and sewer lines broke and power outagesoccurred throughout the island.9 May 2008 Felt on Guam, also felt on Saipan. No reports of damage. 6.7 IVSources: HS/OCD 2003; EERI 1995; WERI 1998; USGS 1978, 1983, 1993, 1997, 2001, 2002, 2008, 2010; Repetti 1948.Surface Fault Rupture: Although surface fault ruptures have not been observed historicallyalong any of the known faults on Guam (Figure D-13), abundant geologic evidence shows thatmany faults ruptured prehistorically in the late Quaternary (past 130,000 years) and, thus, havethe potential for surface rupture. This geologic evidence of prehistoric ruptures includes fault5-20