Pilot Andy Bachner’s account of the 1964 Alaska earthquake

On Friday, March 27, 1964, at about 4:30pm, a 22-year-old pilot named Andy Bachner took off from Fairbanks International Airport on a training flight for Wien Airlines. Alongside Bachner in the single-engine Tri-Pacer plane was the flight instructor, Don Edgar Jonz. Their instrument training flight took them into the clouds and north of Fairbanks 100 miles, in the vicinity of Beaver Creek. Approximately one hour into the flight, Bachner and Jonz abruptly lost all communication with the ground. Fearing a nuclear strike on Eielson and expecting to see Soviet fighter jets, Bachner continued to fly for approximately 30 minutes until fuel was a consideration, prompting them to return to Fairbanks. Upon landing back at Fairbanks, Bachner and Jonz learned about the catastrophic earthquake in southern Alaska. Jonz was asked by the U.S. Army Corps of Engineers to pilot a flight to southern Alaska to survey the earthquake and tsunami damage. Jonz invited Bachner to pilot the plane, allowing Bachner to gain additional instrument training. The two men boarded a Twin Bonanza plane owned by Frontier Flying Service and were provided with a fancy radio. They flew for approximately six hours that night . They live-radioed what they saw in the twilight, fire light, and light of the full moon, while surveying Anchorage, Whittier, Valdez, and Cordova, and then landing back in Fairbanks early March 28th. On Friday, March 27, 1964, at 5:36pm local time, a magnitude 9.2 earthquake struck south-central Alaska. The earthquake devastated Anchorage with its shaking, and it devastated coastal communities with its tsunami. To date, this was the second largest earthquake ever recorded on Earth (1960 magnitude 9.5 in Chile).This collection contains: (1) a pdf of the annotated text and (2) the unedited audio file of the full interview. The edited video interview can be seen on youtube at https://youtu.be/vVIgbBFwaj

Earthquake Stories from Minto and Nenana, Alaska

On Wednesday October 15, 1947 at 4:10pm local time, a magnitude 7.2 earthquake struck Interior Alaska, near Healy. This is a collection of stories of six life-long Alaskan elders who felt this earthquake and shared their recollections in fall of 2014, sixty-seven years after the earthquake. Geraldine Charlie had recently turned 18 years old and worked in the village store in Minto when the earthquake hit. Geraldine was crouching down to weigh a bag of potatoes at the moment the earthquake hit. She felt dizzy and noticed Coleman lanterns swaying from side to side, and items shook off the shelves. Sarah Silas and Berkman Silas were also in Minto and had been married for three years. Sarah recalls watching her toddler son, who laughed as he tried to maintain his balance as the floor rolled back and forth under his feet. Berkman and other men were ice fishing near Little Goldstream Creek when the earthquake hit. Rafting ice caused the men to run for the shore. Paul Esau was near Tolovana working on the roof of their home. Caroline Ketzler was up in their food cache at their home up the Kantishna River. Henry Ketzler was in a cabin in Nenana and ran for the exit, only to hit the door frame as it shook with the entire house. These are their stories from 1947. Also discussed in these stories are the effects from the 1912 Katmai eruption, the 1937 Salcha earthquake, and the 1964 earthquake.These interviews were collected as part of a project funded by the National Science Foundation, grant EAR-1352688, “CAREER: Intraplate tectonics and deep crustal faulting in rural Alaska”. Support was also provided from a subaward from IRIS to UAF ("University of Alaska Fairbanks Geophysical Institute in Support of EarthScope’s Transportable Array"). This subaward is awarded under Cooperative Agreement No. EAR-1261681 issued by the National Science Foundation under CFDA No. 47.050

Assessment of station metadata in Alaska based on analysis of Love waves from the 2012-04-11 Mw 8.6 offshore Sumatra earthquake

This report is part of a detailed investigation of a Mw 3.9 earthquake near Nenana, Alaska, that was triggered by Love waves from a Mw 8.6 offshore Sumatra earthquake. Results from that study appeared in Tape et al. (2013). We analyze all BH and HH channel waveforms that are available at the Alaska Earthquake Center. This report has three objectives: (1) to provide information that may help improve station metadata at Alaska stations; (2) to provide a snapshot of station performance in Alaska at one particular time (11-April-2012); (3) to provide details and figures on part of the waveform processing used in Tape et al. (2013)

Archival search for felt reports for the Alaska earthquake of August 27, 1904

This report documents a search of primary sources from 1904 to identify felt reports of the 1904-08-27 earthquake in central Alaska. The objective is to use the felt reports to get a better idea for where the earthquake occurred.This project was supported by NSF grant EAR-1352668

Analysis of regional seismograms and 3D synthetic seismograms for the 2016-01-24 Mw 7.1 Iniskin earthquake in southern Alaska

I perform two analyses to identify cases of seismogram clipping or other problems (e.g., data gaps) for the 2016-01-24 Mw 7.1 Iniskin, Alaska, earthquake. The first analysis is a comparison of synthetic and observed seismograms: three-component, displacement seismograms filtered between periods 4-80 s. The subset of 141 stations is limited to an oblique rectangular region that is 1200 km x 600 km (Figures 1 and 2) and used in a seismic wavefield simulation with a three-dimensional seismic velocity model. I identify 60 out of 141 stations that are suspected of clipping or other problems. Of the 81 good stations, only 8 are within 250 km of the Iniskin epicenter, and all 8 stations are outside of Cook Inlet basin, which strongly amplifies ground motion (both in data and in synthetics). The second, much simpler, analysis is to identify clipping based on the maximum counts on the waveforms. The max-counts approach reveals general agreeement with the classification based on long-period data and synthetics. The analysis suggests that (1) some recorded waveforms that exceed clipping levels may still be usable for some modeling purposes, and (2) some recorded waveforms that appear to be suitable for modeling purposes should probably be discarded due to clipping at high frequencies. The identification of suspected stations, along with the waveform comparisons, may help network operators assess the possibility of unexpected performance during the Mw 7.1 slab earthquake

Hypocenter estimation for 14 earthquakes in south-central Alaska (1929-1975)

We provide results from an analysis of 14 historical earthquakes in the region of Cook Inlet and Susitna, south-central Alaska. Using global arrival times of P and S waves, we estimate probabilistic hypocenters using the code NonLinLoc. We provide the complete results, as well as a set of plots to help interpret the likelihood of each earthquake being within the crust, on the subduction interface, or within the subducting Pacific slab.V. Silwal and C. Tape were supported by USGS Earthquake Hazards Program (contract G15AP00052)

Step-response signals recorded at seismic stations in Alaska

This technical report documents the occurrence of a "step-response signal" on seismic stations in Alaska. The unwanted signal occurs both during earthquakes and independent of earthquakes. The cause of the signal is unknown to us, though it has previously been identified in the published seismology literature

Step-response signals recorded during earthquakes in Alaska

We present waveform record sections of 18 earthquakes recorded the Minto Flats fault zone in central Alaska. These include the largest earthquakes to have occurred within the Minto Flats fault zone since the installation of the 13-station FLATS network in September 2015 (Tape and West, 2014). Several seismograms from these earthquakes exhibit a ``step-response signal'' that is a long-period, unwanted signal that does not reflect regional ground motion. We use the term ``anomalously high amplitudes'' to refer to amplitudes within a certain bandpass that exceed the amplitude of earthquake ground motion (within the same bandpass). We attribute anomalously high amplitudes to three possibilities: (1) step-response signal due to local tilt or other effect, (2) step-response signal due to defective sensor, (3) digitizer clipping, (4) high noise (especially before the earthquake). We find widespread occurrences of the step-response signal for earthquakes in the Minto Flats fault zone.This project was supported in part by the National Science Foundation under Grant No. EAR-1352668

Seismic tomography of the southern California crust based on spectral-element and adjoint methods

We iteratively improve a 3-D tomographic model of the southern California crust using numerical simulations of seismic wave propagation based on a spectral-element method (SEM) in combination with an adjoint method. The initial 3-D model is provided by the Southern California Earthquake Center. The data set comprises three-component seismic waveforms (i.e. both body and surface waves), filtered over the period range 2–30 s, from 143 local earthquakes recorded by a network of 203 stations. Time windows for measurements are automatically selected by the FLEXWIN algorithm. The misfit function in the tomographic inversion is based on frequency-dependent multitaper traveltime differences. The gradient of the misfit function and related finite-frequency sensitivity kernels for each earthquake are computed using an adjoint technique. The kernels are combined using a source subspace projection method to compute a model update at each iteration of a gradient-based minimization algorithm. The inversion involved 16 iterations, which required 6800 wavefield simulations. The new crustal model, m_(16), is described in terms of independent shear (V_S) and bulk-sound (V_B) wave speed variations. It exhibits strong heterogeneity, including local changes of ±30 per cent with respect to the initial 3-D model. The model reveals several features that relate to geological observations, such as sedimentary basins, exhumed batholiths, and contrasting lithologies across faults. The quality of the new model is validated by quantifying waveform misfits of full-length seismograms from 91 earthquakes that were not used in the tomographic inversion. The new model provides more accurate synthetic seismograms that will benefit seismic hazard assessment

Multiscale estimation of GPS velocity fields

We present a spherical wavelet-based multiscale approach for estimating a spatial velocity field on the sphere from a set of irregularly spaced geodetic displacement observations. Because the adopted spherical wavelets are analytically differentiable, spatial gradient tensor quantities such as dilatation rate, strain rate and rotation rate can be directly computed using the same coefficients. In a series of synthetic and real examples,we illustrate the benefit of themultiscale approach, in particular, the inherent ability of the method to localize a given deformation field in space and scale as well as to detect outliers in the set of observations. This approach has the added benefit of being able to locally match the smallest resolved process to the local spatial density of observations, thereby both maximizing the amount of derived information while also allowing the comparison of derived quantities at the same scale but in different regions.We also consider the vertical component of the velocity field in our synthetic and real examples, showing that in some cases the spatial gradients of the vertical velocity field may constitute a significant part of the deformation. This formulation may be easily applied either regionally or globally and is ideally suited as the spatial parametrization used in any automatic time-dependent geodetic transient detector