Study of recent tsunamis sheds light on earthquakes

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95102/1/eost9964.pd

Fault parameters and tsunami excitation of the May 23, 1989, MacQuarie Ridge Earthquake

The Macquarie Ridge earthquake of May 23, 1989, is one of the largest events in the last decade. Furthermore, it is the largest strike-slip earthquake ever recorded instrumentally. We analyzed long-period surface waves and body waves recorded at global networks (GDSN, IRIS, GEOSCOPE, and IDA) to estimate the fault parameters and computed tsunamis from the estimated parameters. The Centroid Moment Tensor (CMT) solution from surface waves shows that the mechanism is almost pure strike-slip with one of the nodal planes parallel to the strike of the Macquarie Ridge. The seismic moment is 1.6 × 10^(21) Nm (× 10^(28) dyn•cm) and the corresponding moment magnitude is M_w =8.1. Teleseismic P and S waves from 10 stations with good azimuthal coverage are used to model the temporal and spatial distribution of the subevents. Four subevents are located sequentially from south to north along the ridge system in about 30 sec. All of them have a mechanism similar to the CMT solution. The fault length is estimated to be about 120 km from the subevent and the aftershock distributions. The rapture propagates from south to north at a relatively high speed. The average slip on the fault depends on the estimate of the fault width, but is probably larger than 9 m. A large strike-slip earthquake like this event produces significant vertical displacements on the ocean bottom and excites tsunamis. Computation of tsunamis using the estimated fault parameters predicts that small tsunamis are expected at Australia and New Zealand. In fact, small tsunamis were observed on the southern coast of Australia

Broadband Study of the Source Characteristics of the Earthquake

We have determined the source characteristics of the 1989 Loma Prieta earthquake, using teleseismic data. The solution from body waves gives a mechanism with a strike of 128°, a dip of 70° a rake of 138°, and a seismic moment of 3x10^(26)dyne-cm (M_w=6.9). This solution is similar to those obtained from long-period Rayleigh and Love waves, PnJ waves, and first-motion data. The body-wave solution suggests a depth of about 15 km. The effective duration of the source is 6 s, suggesting lengths of 30 and 15 km for bilateral and unilateral faulting, respectively. Considering the extent of the aftershock zones, we estimate a total rupture length of 35 km. The strike-slip and thrust components of coseismic slip are 177 and 159 cm, respectively. The large thrust component raises an important question regarding the recurrence pattern. If the 1989 Loma Prieta earthquake is a characteristic earthquake with a recurrence interval of about 100 yr, the 159-cm displacement implies a long-term uplift rate of about 1 cm/yr, which appears too high for this region. Three hypotheses for reconciling this apparent conflict are that (1) the geometry of plate motion along the Santa Cruz Mountains section of the San Andreas fault changes on a time scale of several thousand years, and so the coseismic displacement has not accumulated enough to produce high topographic relief; (2) the coseismic-slip direction varies from event to event; and (3) the slip plane of the 1989 Loma Prieta earthquake is distinct from the Pacific-North America plate boundary-if so, then this earthquake is a rather rare, noncharacteristic event. The surface slip of about 1 m for the 1906 San Francisco earthquake is one of the key data in long-term forecasting. No surface slip was observed in the 1989 Loma Prieta earthquake, even if the horizontal slip at depth was as large as 1.8 m. This discrepancy points to a risk of relying too heavily on surface observations for long-term seismic-risk analysis

Broadband study of the 1989 Loma Prieta Earthquake

We determined the source characteristics of the Oct. 18, 1989 Loma Prieta, California, earthquake using teleseismic data. The solution from body waves gives a mechanism with dip=70°, rake=138°, and strike=128°, and a seismic moment of 3×10^(26) dyne-cm (M_w=6.9). This solution is similar to those obtained from long-period Rayleigh and Love waves, P_(nL) waves, and first-motion data. The body wave form suggests a depth of about 15 km. The effective duration of the source is 6 sec, which suggests a fault length of 30 km and 15 km for bilateral and unilateral faulting, respectively. Considering the extent of the aftershock area, we used 35 km as an estimate of the total rupture length. The strike-slip and the thrust components of the coseismic slip are 177 and 159 cm, respectively. The large thrust component raises an important question regarding the recurrence pattern. If the Loma Prieta earthquake is a characteristic earthquake with a recurrence interval of about 100 years, the 159 cm displacement implies a long term uplift rate of about 1 cm/year, which appears too large for this region. Three hypotheses for reconciling this apparent conflict are: (1) the geometry of plate motion along the Santa Cruz Mountain segment changes over a time scale of several thousand years so that the coseismic displacement has not accumulated enough to produce high topographic relief; (2) the coseismic sHp direction varies from event to event; (3) the slip plane of the 1989 Loma Prieta earthquake is different from the major boundary between the Pacific and the North American plates; if this is the case, the Loma Prieta earthquake is a rather rare non-characteristic event. The surface slip of about l m for the 1906 San Francisco earthquake is one of the key data in long-term forecasting. No surface slip was observed for the 1989 Loma Prieta earthquake, even if the horizontal slip at depth is as large as 1.8 m. This points to a risk of relying too heavily on surface observations for long-term seismic risk analysis

Tsunami generation by horizontal displacement of ocean bottom

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95068/1/grl9126.pd

Generation mechanism of tsunamis from the 1883 Krakatau Eruption

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94841/1/grl8071.pd

Interleukin-10 containing normal human serum inhibits granzyme B release but not perforin release from alloreactive and EBV-specific T cell clones

Interleukin-10 (IL-10), also known as cytokine synthesis inhibitory factor, has pleiotropic effects in immunoregulation and inflammation. It is capable of inhibiting synthesis of pro-inflammatory cytokines like interferon γ (IFNγ), IL-2, IL-3, tumor necrosis factor α(TNFα) and granulocyte macrophage colony stimulating factor (GM-CSF) made by cells such as macrophages and T helper Type 1 cells. We observed that normal human serum, derived from a healthy individual but containing large amounts of IL-10 (arbitrarily designated as "IL-10 serum"), inhibited cytotoxic activity and interfered with granzyme B release from alloreactive cytotoxic T cell (CTL) clones _in vitro_, but did not affect perforin release. The addition of normal human serum containing high levels of anti-IL-10 IgG (arbitrarily designated as "anti-IL-10 IgG serum") neutralized the inhibitory effects of IL-10 serum. Moreover, we have identified that cytotoxic activity and granzyme B release from an Epstein-Barr virus (EBV)-specific CTL clone was similarly inhibited in the presence of IL-10 serum, while perforin release was unaffected. Anti-IL-10 IgG serum also appeared to neutralize the inhibitory effect of IL-10 serum on an EBV-specific CTL clone

Source parameters of the 1957 Aleutian Earthquake from tsunami waveforms

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94584/1/grl6779.pd

Rupture extent of the 1938 Alaskan earthquake as inferred from tsunami waveforms

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94754/1/grl7445.pd