Geology topics

Heidi D. Stenner

Publications and source records attributed to Heidi D. Stenner.

5 recordsLinked to original sources

USGS2006

The Hayward fault

This field guide consists of eleven stops at sites that illustrate the geological, geophysical, geographic, and engineering aspects of the Hayward fault in the East Bay. Section I (Stops 1–4) consists of stops that are part of the University of California at Berkeley (UC-Berkeley), including research facilities, retrofit of campus buildings, and geomorphic features along the fault. Section II (Stops 5 and 6) consists of stops along the Hayward fault north of the UC-Berkeley main campus, and Section III (stops 7–11) consists of stops related to the Hayward fault south of the UC-Berkeley main campus (Fig. 1 ). Stops are designed to illustrate geomorphic features of the fault, the effects of fault creep on structures sited on the fault, and retrofit design of structures to mitigate potential future deformation due to fault rupture.

California↗

USGS2006

Paleoseismic observations of an onshore transform boundary: The Magallanes-Fagnano fault, Tierra del Fuego, Argentina

We present preliminary information on the geomorphologic features and paleoseismic record associated with the ruptures of two Ms 7.8 earthquakes that struck Tierra del Fuego and the southernmost continental margin of South America on December 17, 1949. The fault scarp was surveyed in several places cast of Lago Fagnano and a trench across a secondary fault trace of the Magallanes-Fagnano fault was excavated at the Ri??o San Pablo. The observed deformation in a 9 kyr-old peat bog sequence suggests evidence for two, and possibly three pre-1949 paleoearthquakes is preserved in the stratigraphy. The scarp reaches heights up to 11 m in late Pleistocene-Holocence(?) deposits, but the vertical component of the 1949 events was always less than ???1 m. This observation also argues for the occurrence of previous events during the Quaternary. Along die part of the fault we investigated east of Lago Fagnano, the horizontal component of the 1949 rupture does not exceed 4 m and is likely lower than 0.4 m, which is consistent with the kinematics of a local releasing bend, or at the end of a strike-slip rupture zone. ?? 2006 Revista de la Asociacio??n Geolo??gica Argentina.

Revista de la Asociacion Geologica Argentina↗

USGS2004

Surface rupture of the 2002 Denali fault, Alaska, earthquake and comparison with other strike-slip ruptures

On 3 November 2002, an M7.9 earthquake produced 340 km of surface rupture on the Denali and two related faults in Alaska. The rupture proceeded from west to east and began with a 40-km-long break on a previously unknown thrust fault. Estimates of surface slip on this thrust are 3-6 m. Next came the principal surface break along ???218 km of the Denali fault. Right-lateral offsets averaged around 5 m and increased eastward to a maximum of nearly 9 m. The fault also ruptured beneath the trans-Alaska oil pipeline, which withstood almost 6 m of lateral offset. Finally, slip turned southeastward onto the Totschunda fault. Right-lateral offsets are up to 3 m, and the surface rupture is about 76 km long. This three-part rupture ranks among the longest strike-slip events of the past two centuries. The earthquake is typical when compared to other large earthquakes on major intracontinental strike-slip faults. ?? 2004, Earthquake Engineering Research Institute.

Earthquake Spectra↗

USGS2004

Surface rupture and slip distribution of the Denali and Totschunda faults in the 3 November 2002 M 7.9 earthquake, Alaska

The 3 November 2002 Denali fault, Alaska, earthquake resulted in 341 km of surface rupture on the Susitna Glacier, Denali, and Totschunda faults. The rupture proceeded from west to east and began with a 48-km-long break on the previously unknown Susitna Glacier thrust fault. Slip on this thrust averaged about 4 m (Crone et al. , 2004) . Next came the principal surface break, along 226 km of the Denali fault, with average right-lateral offsets of 4.5–5.1 m and a maximum offset of 8.8 m near its eastern end. The Denali fault trace is commonly left stepping and north side up. About 99 km of the fault ruptured through glacier ice, where the trace orientation was commonly influenced by local ice fabric. Finally, slip transferred southeastward onto the Totschunda fault and continued for another 66 km where dextral offsets average 1.6–1.8 m. The transition from the Denali fault to the Totschunda fault occurs over a complex 25-km-long transfer zone of right-slip and normal fault traces. Three methods of calculating average surface slip all yield a moment magnitude of M w 7.8, in very good agreement with the seismologically determined magnitude of M 7.9. A comparison of strong-motion inversions for moment release with our slip distribution shows they have a similar pattern. The locations of the two largest pulses of moment release correlate with the locations of increasing steps in the average values of observed slip. This suggests that slip-distribution data can be used to infer moment release along other active fault traces.

Alaska↗

USGS2002

Displaced rocks, strong motion, and the mechanics of shallow faulting associated with the 1999 Hector Mine, California, earthquake

The paucity of strong-motion stations near the 1999 Hector Mine earthquake makes it impossible to make instrumental studies of key questions about near-fault strong-motion patterns associated with this event. However, observations of displaced rocks allow a qualitative investigation of these problems. By observing the slope of the desert surface and the frictional coefficient between these rocks and the desert surface, we estimate the minimum horizontal acceleration needed to displace the rocks. Combining this information with observations of how many rocks were displaced in different areas near the fault, we infer the level of shaking. Given current empirical shaking attenuation relationships, the number of rocks that moved is slightly lower than expected; this implies that slightly lower than expected shaking occurred during the Hector Mine earthquake. Perhaps more importantly, stretches of the fault with 4 m of total displacement at the surface displaced few nearby rocks on 15?? slopes, suggesting that the horizontal accelerations were below 0.2g within meters of the fault scarp. This low level of shaking suggests that the shallow parts of this rupture did not produce strong accelerations. Finally, we did not observe an increased incidence of displaced rocks along the fault zone itself. This suggests that, despite observations of fault-zone-trapped waves generated by aftershocks of the Hector Mine earthquake, such waves were not an important factor in controlling peak ground acceleration during the mainshock.

California↗